Physics (Science 086) · Class X · Chapter-wise Board Questions

Pushkar was studying a light phenomenon and wrote down the following statements in that context :

(i) A concave mirror can be used as a shaving mirror because it can form an enlarged, virtual image when the object is placed between the pole and focus.

(ii) A convex lens always forms real, inverted images, regardless of the position of the object.

(iii) The relationship between object distance (u), image distance (v) and focal length (f) of the lens is given by 1f = 1v − 1u.

Choose the option enlisting all the correct statements :

1. (i) and (ii)
2. (i) and (iii)
3. (ii) and (iii)
4. (i), (ii) and (iii)

Assertion (A) : For a medium of given refractive index, the value of the angle of refraction corresponding to an angle of incidence is not a constant.

Reason (R) : With change in angle of incidence, the value of angle of refraction changes. Hence, the ratio of sine of angle of incidence to sine of angle of refraction remains constant.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

When a convergent beam of light is incident on a convex mirror, the reflected rays appear to be coming from a point 20 cm behind the mirror and retrace their path. The focal length of the mirror is

1. 20 cm
2. 10 cm
3. 40 cm
4. 30 cm

In the given ray diagram the values of the angle of incidence and the angle of reflection are :

1. i = 50°, r = 40°
2. i = 40°, r = 50°
3. i = 40°, r = 40°
4. i = 50°, r = 50°

A convex lens of focal length 15 cm, is forming a real image. If the size of image is same as the size of object, then position of object and position of image will be, respectively :

1. – 15 cm and – 15 cm from lens
2. – 15 cm and + 15 cm from lens
3. – 30 cm and + 30 cm from lens
4. – 30 cm and – 30 cm from lens

From the following options choose the one which gives negative magnification greater than one :

1. Concave mirror; Nature of image – real
2. Concave mirror; Nature of image – virtual
3. Convex mirror; Nature of image – real
4. Convex mirror; Nature of image – virtual

Rays from the sun converge at a point 25 cm behind a convex lens. The distance at which an object be placed in front of the lens to get a virtual image, is :

1. 20 cm
2. 40 cm
3. 50 cm
4. More than 50 cm

Mirror ‘X’ is used to concentrate sunlight in solar furnace and Mirror ‘Y’ is fitted on the side of the vehicle to see the traffic behind the driver. Which of the following statements are true for the two mirrors ?

(i) The image formed by mirror ‘X’ is real, diminished and at its focus.

(ii) The image formed by mirror ‘Y’ is virtual, diminished and erect.

(iii) The image formed by mirror ‘X’ is virtual, diminished and erect.

(iv) The image formed by mirror ‘Y’ is real, diminished and at its focus.

1. (i) and (ii)
2. (ii) and (iii)
3. (iii) and (iv)
4. (i) and (iv)

If the absolute refractive indices of two media X and Y are 65 and 43 respectively, then the refractive index of Y with respect to X will be :

1. 109
2. 910
3. 98
4. 89

An object is placed at a distance of 30 cm from the pole of a concave mirror. If its real and inverted image is formed at 60 cm in front of the mirror, the focal length of the mirror is :

1. – 15 cm
2. – 20 cm
3. + 20 cm
4. + 15 cm

Absolute refractive index of water and glass is 43 and 32 respectively. If the speed of light in glass is 2 × 10⁸ m/s, the speed of light in water is :

1. 94 m/s
2. 73 m/s
3. 169 m/s
4. 98 m/s

To get an image of magnification –1 on a screen using a lens of focal length 20 cm, the object distance must be :

1. Less than 20 cm
2. 30 cm
3. 40 cm
4. 80 cm

An optical device ‘X’ is placed obliquely in the path of a narrow parallel beam of light. If the emergent beam gets displaced laterally, the device ‘X’ is :

1. plane mirror
2. convex lens
3. glass slab
4. glass prism

In order to obtain large images of the teeth of patients, the dentist holds the concave mirror in such a manner that the teeth are positioned

1. at the focus of mirror.
2. between pole and focus of the mirror.
3. between focus and centre of curvature of the mirror.
4. at the centre of curvature of the mirror.

Identify from the following the ray diagram which shows the correct path of the reflected ray for the ray incident on a concave mirror as shown :

A 5 cm long rod is placed vertically in front of a concave mirror. If its 5 cm long image is formed at 20 cm in front of the mirror, the focal length of the mirror is :

1. − 20 cm
2. − 10 cm
3. − 5 cm
4. 20 cm

An optical device which always produces images of m = + 1 is :

1. Plane mirror
2. Convex mirror
3. Concave mirror
4. Convex lens

At what distance from a convex lens should an object be placed to get an image of the same size as that of the object on a screen ?

1. Beyond twice the focal length of the lens.
2. At the principal focus of the lens.
3. At twice the focal length of the lens.
4. Between the optical centre of the lens and its principal focus.

Absolute refractive index of glass and water is 32 and 43 respectively. If the speed of light in glass is 2 × 10⁸ m/s, the speed of light in water is :

1. 94 × 10⁸ m/s
2. 52 × 10⁸ m/s
3. 73 × 10⁸ m/s
4. 169 × 10⁸ m/s

How will the image formed by a convex lens be affected, if the upper half of the lens is wrapped with a black paper ?

1. The size of the image formed will be one-half of the size of the image due to complete lens.
2. The image of upper half of the object will not be formed.
3. The brightness of the image will reduce.
4. The lower half of the inverted image will not be formed.

The colour of light for which the refractive index of glass is minimum, is :

1. Red
2. Yellow
3. Green
4. Violet

The image formed by a concave mirror of focal length 50 cm is real and of magnification – 1. In this case the distance between the object from its own image is :

1. 50 cm
2. 100 cm
3. 200 cm
4. Zero

An object is placed in front of a convex mirror at infinity. According to the New Cartesian Sign Convention, the sign of the focal length and the sign of the image distance in this case are respectively :

1. + , −
2. − , +
3. − , −
4. + , +

A student wants to obtain an erect image of an object using a concave mirror of 10 cm focal length. What will be the distance of the object from mirror ?

1. Less than 10 cm
2. 10 cm
3. between 10 cm and 20 cm
4. more than 20 cm

When an object is placed beyond 2F of a convex lens, the nature of the image formed is :

1. Real, inverted and diminished
2. Real, erect and magnified
3. Virtual, erect and magnified
4. Real, inverted and magnified

Arnav was making notes and he wrote down the following statements from his understanding of reflection from curved surfaces.

I. Concave mirrors can produce both real and virtual images depending on the position of the object.

II. Convex mirrors always produce real, inverted images regardless of the object’s position.

III. In both concave and convex mirrors, the image location can be determined using the mirror formula 1f = 1v + 1u where f is the focal length, v is the image distance, and u is the object distance.

Choose from the following the correct option that lists the correct statements about reflection from curved surfaces.

1. I and II
2. I, II and III
3. II and III
4. I and III

The following question consists of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:

Assertion (A): A point object is placed at a distance of 26 cm from a convex mirror of focal length 26 cm. The image will not form at infinity.

Reason (R): For above given system the equation 1f = 1v + 1u gives v = ∞.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, and R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

A student wants to determine the focal length of a convex lens using sunlight. Which of the following practical procedures will give the most accurate result?

1. Move the lens close to a wall and measure the blurred circle.
2. Hold the lens above a sheet of paper and adjust until the smallest, brightest spot is formed.
3. Measure the thickness of the lens with a scale.
4. Look through the lens at a distant object.

The following one question consists of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:

Assertion (A): The apparent depth of a coin in water is less than its real depth.

Reason (R): Light bends away from the normal when it travels from water to air.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, and R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

The given figure shows image formation by a lens. Analyse the figure and answer the following questions :

(a) What is the type of lens used for image formation in the given ray diagram ?

(b) If the real image is formed at a distance of 30 cm from the lens and the size of image is twice the size of the object, then where was the object placed ?

With the help of the given ray diagram, calculate the refractive index of Medium 2 with respect to Medium 1.

(Given that √3 = 1·732)

A ray of light enters into medium B from medium A as shown in the given figure :

(a) Which one of these two media is optically denser than the other medium ? Justify your answer.

(b) If the speed of light in medium A is V_A and in medium B is V_B, then what is the refractive index of medium B with respect to medium A ?

(a) Relate the speed of light in the given medium with its optical density.

(b) Using the information given in the table below, arrange the medium A, B and C in the ascending order of their optical density.

An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm. Use lens formula to find the position of the image formed in this case.

(a) Out of the two lenses, one concave and the other convex, state which one will diverge a parallel beam of light falling on it. Draw a ray diagram to show the principal focus of the lens.

OR

(b) A ray of light after refraction from a convex lens emerges parallel to its principal axis.

(i) Draw a labelled ray diagram to show it.

(ii) In this case, the incident ray before refraction from the lens passes through a point on its principal axis. Name the point.

The values of absolute refractive indices of kerosene and water are 1.44 and 1.33 respectively. Compare the two media on the basis of their

(a) optical density

(b) mass density

(c) relative speed of propagation of light.

What do you infer on the basis of above comparisons ?

Study the figure in which the path of a ray of light going from Medium 1 to Medium 2 is shown.

(a) Out of the two Media – Medium 1 and Medium 2, in which is the speed of light more ?

(b) State reason of bending of the refracted ray away from the normal.

(c) Express refractive index of Medium 2 with respect to Medium 1 in terms of speed of light in two media.

An object is placed 25 cm in front of a concave mirror of focal length 15 cm. Use mirror formula and new cartesian sign convention to determine the position of the image formed.

An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position of the image formed by the mirror.

(a) State two laws of refraction of light.

OR

(b) Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is 3 × 10⁸ m/s.

The heat produced at a point due to concentration of sunlight by a convex lens burns a paper.

(a) Explain why it happens.

(b) Name the term (in the context of the lens used) given to the point at which the paper starts burning. What does the bright spot formed on the paper represent ?

Draw a labelled ray diagram to show the formation of image due to a concave mirror when an object is placed between its pole and principal focus.

A light ray enters from medium A to medium B as shown in the figure.

(a) Which one of the two media is denser w.r.t. other medium ? Justify your answer. [1]

(b) If the speed of light in medium A is v_a and in medium B is v_b, what is the refractive index of B with respect to A. [1]

OR

(a) A ray of light starting from diamond is incident on the interface separating diamond and water. Draw a labelled ray diagram to show the refraction of light in this case. [1]

(b) Absolute refractive indices of diamond and water are 2.42 and 1.33 respectively. Find the value of refractive index of water w.r.t. diamond. [1]

(a) Find the magnification of the image formed by a spherical mirror from the following data :
u = – 20 cm, f = – 15 cm.

OR

(b) Draw a labelled ray diagram for the image formation by a concave mirror when an object is placed between its centre of curvature and focus.

The above image shows the formation of an image with an optical instrument.

A. Identify the optical instrument (shown schematically as a rectangle) in the image.

B. What type of image is formed in this case?

C. Based on the measurements given in the image, calculate the focal length of the instrument.

A. State Snell’s Law of refraction.

B. Define the refractive index of a material with respect to another material giving the mathematical expression.

(a) Write the expression for the magnification produced by a lens in terms of object distance and image distance.

(b) A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. Calculate the size of the image formed, if the distance of the object from the lens is 10 cm.

(a) Observe the given ray diagram and compare :

(i) the speed of light in medium A and the speed of light in medium B.

(ii) the optical densities of medium B and medium C.

(b) Draw a ray diagram for refraction where the optical density of medium ‘A’ becomes equal to the optical density of medium ‘C’ and optical density of medium ‘B’ is greater than the optical density of medium ‘A’ and medium ‘C’.

(a) A ray of light after reflection from a concave mirror becomes parallel to its principal axis. Draw a labelled ray diagram to show this.

(b) (i) Differentiate between the virtual images formed by a convex mirror and concave mirror.

(ii) “The value of magnification ‘m’ for a mirror is –2.” Calculate the height of object if the height of image is 20 cm.

Draw ray diagrams to show the nature, position and relative size of the image formed by a convex mirror when the object is placed (i) at infinity and (ii) between infinity and pole P of the mirror.

A convex lens forms an 8·0 cm long image of a 2·0 cm long object which is kept at a distance of 6·0 cm from the optical centre of the lens. If the object and the image are on the same side of the lens, find (i) the nature of the image, (ii) the position of the image, and (iii) the focal length of the lens.

If we want to obtain a virtual and magnified image of an object by using a concave mirror of focal length 18 cm, where should the object be placed? Use mirror formula to determine the object distance for an image of magnification +2 produced by this mirror to justify your answer.

The power of a lens is –0.25 D. Based on this information, find out

(a) The type of lens and its focal length.

(b) The eye defect for which it may be used as a corrective lens.

(c) The nature and size of the image formed by this lens when an object is placed between F and 2F from the optical centre of this lens.

A student placed a candle flame at different distances from a convex lens and focused its image on a screen. He recorded his observation in tabular form as given below :

Analyse the observation table and on the basis of your analysis only, answer the following questions (without doing any calculations) :

(a) What is the focal length of the convex lens used ? Give reason to justify your answer.

(b) Which one of the sets of observations is not correct and why ?

(c) Draw ray diagram to show image formation for any correct set of observation.

(a) Complete the following ray diagram to show the formation of image :

(b) Mention the nature, position and size of the image formed in this case.

(c) State the sign of the image distance in this case using the Cartesian sign convention.

(a) A student has focussed the image of an object of height 3 cm on a white screen using a concave mirror of focal length 12 cm. If the distance of the object from the mirror is 18 cm, find the values of the following :

(i) Distance of the image from the mirror

(ii) Height of the image

OR

(b) Define power of a lens. The focal length of a lens is – 10 cm. Write the nature of the lens and find its power. If an object is placed at a distance of 20 cm from the optical centre of this lens, according to the New Cartesian Sign Convention, what will be the sign of magnification in this case ?

(A) Define the following terms in the context of a diverging mirror :

(i) Principal focus

(ii) Focal length

Draw a labelled ray diagram to illustrate your answer.

OR

(B) An object of height 10 cm is placed 25 cm away from the optical centre of a converging lens of focal length 15 cm. Calculate the image-distance and height of the image formed.

The power of a lens is +4D. Find the focal length of this lens. An object is placed at a distance of 50 cm from the optical centre of this lens. State the nature and magnification of the image formed by the lens and also draw a ray diagram to justify your answer.

(a) (i) An object of 5 cm height is placed at a distance of 20 cm from the optical centre of a concave lens of focal length 18 cm. Calculate (1) image distance and (2) the magnification in this case.

(ii) Compare the values of magnification obtained by a concave lens and a convex lens when both the lenses form virtual images.

OR

(b) A convex lens can form a (i) real, inverted and magnified image as well as (ii) virtual, erect and magnified image of an object. If the focal length of the lens is 10 cm, what should be the range of the object distance in both cases ? Draw ray diagrams to justify your answer.

A concave lens forms an image that is 1/3rd the size of the object, as shown in the diagram. If the object is placed 24 cm in front of the lens, determine:

A. the type of lens.

B. the image distance

C. the focal length of the lens

Read the following passage and answer the questions given :

Lenses can form different types of images depending upon their focal length and position of object. A convex lens can create real, inverted or virtual, erect images, while a concave lens forms only virtual and diminished images. The focal length determines the power of lens. Convex lenses have positive focal length while concave lenses have negative focal length by convention. When lenses are placed together, their combined power is determined by the sum of their individual powers. Ray diagrams help to visualize how light converges or diverges through lens to form an image.

(a) A convex lens of focal length 20 cm is used to form an image. If an object is placed at 40 cm from the lens, what will be the position and nature of image ? [1]

(b) Illustrate the formation of image with the help of ray diagram, when the object is placed between the optical centre and principal focus of concave lens. [1]

(c) (i) A lens combination consists of a convex lens of focal length 30 cm and a concave lens of focal length 15 cm placed together. Find the equivalent focal length and power of this lens combination. [2]

OR

(c) (ii) Two lenses are placed in contact. One is a concave lens with focal length 2 m and the other is a convex lens with focal length 1.5 m. What type of lens will the combination behave as (convex or concave) ? Give reason. [2]

The variation of image distance (v) with the object distance (u) for a convex lens is given in the following observation table. Analyse it and answer the questions given below :

(a) Without calculation, find out the focal length of the given convex lens. Justify your answer. [1]

(b) Which one of the observations given in the table is not correct and why ? [1]

(c) (i) Find out the value of magnification for u = – 30 cm. Write the nature of the image formed. Give reason for your answer. [2]

OR

(c) (ii) Analyse the data given in the table above and draw the labelled ray diagram for u = – 30 cm and v = 150 cm. [2]

The above ray diagram is to show image formation by a reflecting telescope. Reflecting telescope revolutionized our way of looking into the sky. Reflecting telescopes employ large mirrors to gather and focus light rather than relying solely on lenses as we do in the refracting telescopes. These telescopes utilize precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where the telescope forms an image for observation.

(a) What kind of image of a star is seen by the observer in the eye-piece ? [1]

(b) What kind of mirror is used in this reflecting telescope ? [1]

(c) Explain with the reason, what kind of optical device (type of lens or mirror) is used at the eye-piece. [2]

OR

(c) What is the role of plane mirror in image formation by this telescope ? [2]

Study the data given below showing the focal length of three concave mirrors A, B and C and the respective distances of objects placed in front of the mirrors :

(i) In which one of the above cases the mirror will form a diminished image of the object ? Justify your answer. [1]

(ii) List two properties of the image formed in case 2. [1]

(iii) (A) What is the nature and size of the image formed by mirror C ? Draw ray diagram to justify your answer. [2]

OR

(iii) (B) An object is placed at a distance of 18 cm from the pole of a concave mirror of focal length 12 cm. Find the position of the image formed in this case. [2]

A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors – plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface.

(a) Define the principal axis of a concave mirror. [1]

(b) A ray of light is incident on a concave mirror, parallel to its principal axis. If this ray after reflection from the mirror passes through the principal axis from a point at a distance of 10 cm from the pole of the mirror, find the radius of curvature of the mirror. [1]

(c) (i) An object is placed at a distance of 10 cm from the pole of a convex mirror of focal length 15 cm. Find the position of the image. [2]

OR

(c) (ii) A mirror forms a virtual, erect and diminished image of an object. Identify the type of this mirror. Draw a ray diagram to show the image formation in this case. [2]

In our laboratories we use compound microscopes to see the magnified image of a microscopic object. A compound microscope is made up of two lenses. The lens nearest to the object to be viewed, called objective lens, forms real, inverted and magnified image of the object. This image serves as an object for the second lens called eyepiece. The eyepiece forms virtual, erect and magnified image of its object. Thus, the resultant image formed by a microscope is virtual, inverted and magnified with respect to the microscopic object viewed.

(a) The image of an object formed by a convex lens of focal length 2 cm is real, inverted and magnified. What is the range of object distance in this case ? [1]

(b) The image of an object formed by a convex lens of focal length 6 cm is virtual, erect and magnified. What is the range of object distance in this case ? [1]

(c) (i) An object is placed at a distance of 12 cm from the optical centre of a convex lens of focal length 18 cm. Draw a labelled ray diagram to show the formation of image in this case. [2]

OR

(c) (ii) The image formed by a convex lens is real, inverted and of the same size as the object. If the distance between the objects and the image is 60 cm, determine the focal length of the lens. Give justification for your answer. [2]

Hold a concave mirror in your hand and direct its reflecting surface towards the sun. Direct the light reflected by the mirror on to a white card-board held close to the mirror. Move the card-board back and forth gradually until you find a bright, sharp spot of light on the board. This spot of light is the image of the sun on the sheet of paper; which is also termed as “Principal Focus” of the concave mirror.

(a) List two applications of concave mirror. [1]

(b) If the distance between the mirror and the principal focus is 15 cm, find the radius of curvature of the mirror. [1]

(c) Draw a ray diagram to show the type of image formed when an object is placed between pole and focus of a concave mirror. [2]

OR

(c) An object 10 cm in size is placed at 100 cm in front of a concave mirror. If its image is formed at the same point where the object is located, find : [2]

(i) focal length of the mirror, and

(ii) magnification of the image formed with sign as per Cartesian sign convention.

The ability of a medium to refract light is expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density. On comparing two media, the one with the large refractive index is optically denser medium than the other. The other medium with a lower refractive index is optically rarer. Also the speed of light through a given medium is inversely proportional to its optical density.

(i) Determine the speed of light in diamond if the refractive index of diamond with respect to vacuum is 2.42. Speed of light in vacuum is 3×10⁸ m/s. [1]

(ii) Refractive indices of glass, water and carbon disulphide are 1.5, 1.33 and 1.62 respectively. If a ray of light is incident in these media at the same angle (say θ), then write the increasing order of the angle of refraction in these media. [1]

(iii) (A) The speed of light in glass is 2×10⁸ m/s and in water is 2.25×10⁸ m/s. [2]

(a) Which one of the two is optically denser and why ?

(b) A ray of light is incident normally at the water-glass interface when it enters a thick glass container filled with water. What will happen to the path of the ray after entering the glass ? Give reason.

OR

(iii) (B) The absolute refractive indices of water and glass are 43 and 32 respectively. If the speed of light in glass is 2×10⁸ m/s, find the speed of light in (i) vacuum and (ii) water. [2]

Many optical instruments consist of a number of lenses. They are combined to increase the magnification and sharpness of the image. The net power (P) of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses P₁, P₂, P₃ … as

P = P₁ + P₂ + P₃ …

This is also termed as the simple additive property of the power of lens, widely used to design lens systems of cameras, microscopes and telescopes. These lens systems can have a combination of convex lenses and also concave lenses.

(a) What is the nature (convergent / divergent) of the combination of a convex lens of power + 4 D and a concave lens of power – 2 D ? [1]

(b) Calculate the focal length of a lens of power – 2·5 D. [1]

(c) Draw a ray diagram to show the nature and position of an image formed by a convex lens of power + 0·1 D, when an object is placed at a distance of 20 cm from its optical centre. [2]

OR

(c) How is a virtual image formed by a convex lens different from that formed by a concave lens ? Under what conditions do a convex and a concave lens form virtual images ? [2]

A student took three concave mirrors of different focal lengths and performed the experiment to see the image formation by placing an object at different distances with these mirrors as shown in the following table.

Now answer the following questions :

(a) List two properties of the image formed in Case I. [1]

(b) In which one of the cases given in the table, the mirror will form real image of same size and why ? [1]

(c) Name the type of mirror used by dentists. Give reason why do they use such type of mirrors. [2]

OR

(c) Look at the table and identify the situation (object distance and focal length) which resembles the situation in which concave mirrors are used as shaving mirrors ? Draw a ray diagram to show the image formation in this case. [2]

When a ray of light moving in a medium enters obliquely into another medium, it bends from its path. This phenomenon is called refraction of light. The ability of a medium to refract light is also expressed in terms of optical density. It is not the same as mass density. We use the terms ‘rarer medium’ and ‘denser medium’ which actually means ‘optically rarer medium’ and ‘optically denser medium’ respectively. When we say that a medium ‘A’ is optically denser than the other medium ‘B’, we mean that the refractive index of medium A is more than the refractive index of medium ‘B’. The speed of light is higher in a rarer medium than a denser medium. Thus a ray of light travelling from a rarer medium to a denser medium slows down and bends towards the normal.

(a) Define the term absolute refractive index of a medium. [1]

(b) Absolute refractive indices of water and glass are 43 and 32 respectively.

(i) In which one of the two media is the speed of light more ?

(ii) If a ray of light enters obliquely from glass to water, will it bend towards the normal or away from the normal ? [1]

(c) The absolute refractive indices of water and glass are 43 and 32 respectively. If the speed of light in glass is 2 × 10⁸ m/s, find the speed of light in (i) water and (ii) vacuum. [2]

OR

(c) “A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.” Draw a labelled ray diagram to justify this statement. [2]

The above image is that of a Digital Single Lense Reflector (DSLR) Camera which are used to take high resolution photographs by professional photographers. The second image of the above two is a schematic diagram of how an image is formed on the sensor of the camera. Based on your understanding of the lenses, answer the following questions.

A. What type of lens is used in the DSLR camera shown in the image?

B. What type of image is formed on the sensor?

Attempt either subpart C or D.

C. A photographer is using a DSLR camera with a lens of focal length f = 50 mm to take a close-up photograph of a small object. The lens projects an image onto the camera sensor that is located 60 mm behind the lens. Calculate the object distance (i.e., the distance between the object and the lens).

OR

D. A photographer is using a DSLR camera to take a picture of a flower. The flower is positioned 150 mm away from the camera lens. The actual height of the flower is 80 mm, and the image height formed on the camera’s sensor is measured to be 20 mm. Calculate the focal length of the camera lens.

(A) (i) In which mirror we can always see the full image of a distant object ? Support your answer by a ray diagram for it.

(ii) A convex mirror forms an erect image of an object of size, one-third of the size of the object. Find the position of the object if the radius of curvature of convex mirror is 30 cm.

OR

(B) (i) Define the optical centre of a lens.

(ii) The light from an object placed on a meter scale at 8 cm mark, was focused on a white screen placed at 92 cm mark, with the help of a converging lens placed on the scale at 50 cm mark :

(I) Find the focal length of converging lens.

(II) Find the position of image if the object is shifted towards the lens and kept at 29 cm mark.

(III) What will be the nature of the image formed if the object is further shifted towards the lens ?

(a) (i) The power of a lens ‘X’ is – 2·5 D. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens ?

(ii) ‘‘The value of magnification ‘m’ for a lens is – 2.’’ Using new Cartesian Sign Convention and considering that an object is placed at a distance of 20 cm from the optical centre of this lens, state :

(I) the nature of the image formed;

(II) size of the image compared to the size of the object;

(III) position of the image, and

(IV) sign of the height of the image.

(iii) The numerical values of the focal lengths of two lenses A and B are 10 cm and 20 cm respectively. Which one of the two will show higher degree of convergence/divergence ? Give reason to justify your answer.

OR

(b) (i) Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass.

(ii) State Snell’s law of refraction of light.

(iii) Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of :

(I) object distance, and

(II) magnification.

(a) (i) “In refraction of light through a rectangular glass slab, the emergent ray is always parallel to the direction of the incident ray.” Why ? Explain with the help of a ray diagram. What happens when a ray of light falls normally on one of the faces of a rectangular glass prism ? Draw diagram.

(ii) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 20 cm. Use Lens formula to determine the position of the image formed in this case.

OR

(b) (i) A student wishes to study the image formation by a concave mirror using candle flame as object. State the type of the image formed by the mirror and mention the change in the image formed, if any, that he observes when the candle flame is gradually moved away from the pole of the mirror. Draw a ray diagram to show the image formation when the object distance is nearly equal to the radius of curvature of the mirror.

(ii) A convex mirror used for rear-view on an automobile has a focal length of 3·0 m. If a bus is located at 6·0 m from this mirror, use mirror formula to find the position of the image of the bus as seen in the mirror.

(A) (a) Observe the following diagram and compare (i) speed of light and (ii) optical densities of the three media A, B and C. Also give justification for your answer of any one of the two cases in terms of refractive indices of A, B and C.

(b) Redraw the path of a ray of light through the three media, if the ray of light starting from medium A falls on the medium B

(i) Obliquely and the optical density of medium B is made more than that of A and C.

(ii) The ray falls normally from medium A to medium B.

OR

(B) Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :

(a) Determine the focal length of the lens. Give reason for your answer.

(b) Find magnification of the image formed in Observation No. 3.

(c) The numerical value of magnifications in cases of observation 1 and 2 is same. List two differences in the images formed in these two cases.

(a) Upper half of a convex lens is covered with a black paper. Draw a ray diagram to show the formation of image of an object placed at a distance of 2F from such a lens. Mention the position and nature of the image formed. State the observable difference in the image obtained if the lens is uncovered. Give reason to justify your answer.

(b) An object is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine the distance of the image from the optical centre of the lens.

(a) (i) Draw a ray diagram to show the path of the refracted ray in each of the following cases :

A ray of light incident on a concave lens

(1) parallel to its principal axis, and

(2) is directed towards its principal focus.

(ii) A 4 cm tall object is placed perpendicular to the principal axis of convex lens of focal length 24 cm. The distance of object from the lens is 16 cm. Find the position and size of image formed.

OR

(b) (i) Draw a ray diagram to show the path of the reflected ray in each of the following cases :

A ray of light incident on a convex mirror

(1) parallel to its principal axis, and

(2) is directed towards its principal focus

(ii) A 1.5 cm tall candle flame is placed perpendicular to the principal axis of a concave mirror of focal length 12 cm. If the distance of the flame from the pole of the mirror is 18 cm, use mirror formula to determine the position and size of the image formed.

(a) The variation of image distance (v) with object distance (u) for a convex lens is given in the following observation table. Analyse it and answer the questions that follow :

(i) Without calculation, find the focal length of the convex lens. Justify your answer.

(ii) Which observation is not correct ? Why ? Draw ray diagram to find the position of the image formed for this position of the object.

(iii) Find the approximate value of magnification for u = − 30 cm.

OR

(b) (i) Define principal axis of a lens. Draw a ray diagram to show what happens when a ray of light parallel to the principal axis of a concave lens passes through it.

(ii) The focal length of a concave lens is 20 cm. At what distance from the lens should a 5 cm tall object be placed so that its image is formed at a distance of 15 cm from the lens ? Also calculate the size of the image formed.

(a) An object is placed in front of a convex lens of focal length f. If the distance of the object from the lens is 2f, draw a ray diagram to show the formation of the image. Write the value of magnification in this case.

(b) A student has focussed the image of a candle flame on a white screen using a convex lens. The situation is as given below :

Length of the flame = 2 cm
Focal length of the lens = 12 cm
Distance of the flame from the lens = 16 cm

If the flame is perpendicular to the principal axis of the lens, calculate the values of the following :

(i) Distance of the image from the lens

(ii) Length of the image formed

When you look at an object very close to your eyes, the :

1. Ciliary muscles of your eye contract and the eye lens becomes thick.
2. Ciliary muscles of your eye get relaxed and the eye lens becomes thick.
3. Ciliary muscles of your eye contract and the eye lens becomes thin.
4. Ciliary muscles of your eye get relaxed and the eye lens becomes thin.

Directions : For question number 32, two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer to this question from the codes (A), (B), (C) and (D) as given below :

1. Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

Assertion (A) : When rays of white light pass through a prism, on emerging they give spectrum of seven colours.

Reason (R) : It is due to the scattering of light that red light bends minimum and violet light bends the maximum.

A thin beam of white light falls on a face of a glass prism and a spectrum is obtained on a screen. Which of the following options is the correct sequence of colours from top to bottom on the screen ?

1. Red, Green, Yellow, Violet, Blue
2. Red, Yellow, Green, Blue, Violet
3. Violet, Blue, Green, Yellow, Red
4. Violet, Red, Green, Yellow, Blue

Observe the given ray diagram showing refraction through a prism and choose the correct option for colour of rays 1 and 2 :

The pair of eye parts responsible for admitting different amount of light in to the eyes is

1. Iris and pupil
2. Ciliary muscles and pupil
3. Retina and Iris
4. Ciliary muscles and cornea

The vision defect which arises due to gradual weakening of the ciliary muscles and diminishing flexibility of eye lens is :

1. Myopia
2. Hypermetropia
3. Presbyopia
4. Myopia and hypermetropia both

To restore clear vision in persons whose size of the eye ball has reduced, he/she is suggested to use suitable

1. Converging lens
2. Diverging lens
3. Bifocal lens
4. Cylindrical lens

An old person is suffering from an eye defect caused by weakening of ciliary muscles and diminishing flexibility of the eye lens. If the defect of vision is ‘a’ which can be corrected by lens ‘b’, then ‘a’ and ‘b’ respectively are :

1. hypermetropia and convex lens
2. presbyopia and bifocal lens
3. myopia and concave lens
4. myopia and bifocal lens

In the given figure the angle of incidence and the angle of deviation respectively are :

1. 1 and 5
2. 7 and 6
3. 7 and 4
4. 1 and 6

When a beam of white light passes through a region of very fine dust particles, the colour of light that scatters the most in that region is :

1. red
2. orange
3. blue
4. yellow

Question Nos. 17 to 20 consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option (a), (b), (c) and (d) as given below :

1. Both, Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
2. Both, Assertion (A) and Reason (R) are true, and Reason (R) is not the correct explanation of Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

Assertion (A) : When ciliary muscles contract, eye lens becomes thin.

Reason (R) : Ciliary muscles control the power of the eye lens.

The possible way to restore clear vision of those people whose eyeball has elongated is the use of suitable

1. bifocal lens
2. concave lens
3. converging lens
4. convex lens

The part of human eye which controls the amount of light entering into it.

1. Iris
2. Cornea
3. Ciliary muscles
4. Pupil

Assertion (A) : Due to scattering of sunlight, the clear sky predominantly appears blue.

Reason (R) : The wavelength of blue light is nearly 1·8 times the wavelength of red light.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

The lens system of human eye forms an image on a light sensitive screen, which is called as :

1. Cornea
2. Ciliary muscles
3. Optic nerves
4. Retina

Assertion (A) : The rainbow is a natural spectrum of sunlight in the sky.

Reason (R) : Rainbow is formed in the sky when the sun is overhead and water droplets are also present in air.

For Q. Nos. 17 to 20, two statements are given – One labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below :

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

Consider the following statements in the context of human eye :

(a) The diameter of the eye ball is about 2.3 cm.

(b) Iris is a dark muscular diaphragm that controls the size of the pupil.

(c) Most of the refraction for the light rays entering the eye occurs at the crystalline lens.

(d) While focusing on the objects at different distances the distance between the crystalline lens and the retina is adjusted by ciliary muscles.

The correct statements are –

1. (a) and (b)
2. (a), (b) and (c)
3. (b), (c) and (d)
4. (a), (c) and (d)

Q. Nos. 17 to 20 are Assertion – Reason based questions : These questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below :

Assertion (A) : Myopic eye cannot see distant objects distinctly.

Reason (R) : For the correction of myopia converging lenses of appropriate power are prescribed by eye-surgeons.

1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3. (A) is true, but (R) is false.
4. (A) is false, but (R) is true.

The Phenomena of light involved in the formation of a rainbow in the sky are

1. Refraction, dispersion and reflection
2. Refraction, dispersion and total internal reflection
3. Dispersion, scattering and reflection
4. Dispersion, refraction and internal reflection

Q. Nos. 17 to 20 consists of two statements – Assertion (A) and Reason (R), answer these questions selecting the appropriate option given below :

Assertion (A) : Red light signals are used to stop the vehicles on the road.

Reason (R) : Red coloured light is scattered the most so as to be visible from a large distance.

1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true and (R) is not correct explanation of (A).
3. (A) is true, but (R) is false.
4. (A) is false, but (R) is true.

When a beam of white light passes through a region having very fine dust particles, the colour of light mainly scattered in that region is :

1. Red
2. Orange
3. Blue
4. Yellow

The phenomena of light involved in the formation of rainbow are :

1. Refraction, reflection and dispersion
2. Refraction, dispersion and internal reflection
3. Reflection, dispersion and internal reflection
4. Refraction, dispersion, scattering and total internal reflection

For Questions number 17 to 20, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer from the codes (a), (b), (c) and (d) as given below.

Assertion (A) : A person suffering from myopia cannot see the distant objects clearly.

Reason (R) : A converging lens is used for the correction of myopic eye as it can form real as well as virtual images of the objects placed in front of it.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

In the following diagram showing dispersion of white light by a glass prism, the colours ‘P’ and ‘Q’ respectively are –

1. Red and Violet
2. Violet and Red
3. Red and Blue
4. Orange and Green

In human eye the part which allows light to enter into the eye is –

1. Retina
2. Pupil
3. Eye lens
4. Cornea

When a narrow beam of white light passes through a glass prism it splits into its component colours ? This phenomenon is called :

1. Diffusion of light
2. Total reflection of light
3. Scattering of light
4. Dispersion of light

For Questions number 17 to 20, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

Assertion (A) : A rainbow is an artificial spectrum of white light appearing in the sky after a rain shower.

Reason (R) : The water droplets act like small prisms.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

Choose the correct option from the below which explains the reason for us to perceive the day sky as blue.

1. As sunlight passes through the atmosphere, shorter wavelengths, such as blue are scattered more than other colors.
2. The sky appears blue because all colors are scattered equally, but blue light is stronger and more visible to the human eye.
3. The blue color of the sky is due to longer wavelengths like red and orange scattering more than shorter wavelengths, making blue stand out more.
4. The atmosphere contains blue-colored particles that give the sky its blue appearance.

(A) What is meant by scattering of light ? How do our observations differ when white light (sun light) is scattered from (i) very fine particles of the medium and (ii) very large particles of the medium ?

OR

(B) With the help of a ray diagram, explain a phenomenon of formation of spectrum in nature.

Attempt either (a) or (b) :

(a) How does the focal length of eye lens change as the distance of the object from the eyes is altered ? Explain.

OR

(b) Why is the concave lens used as a corrective lens for a myopic eye ?

Attempt either (a) or (b) :

(a) What happens when light is scattered from (i) very fine particles and (ii) very large size particles of medium ? Justify your answer in each case.

OR

(b) With the help of a ray diagram, explain any phenomenon of formation of spectrum in nature.

(A) (i) How does the change in curvature of the eye lens helps us in the process of seeing the nearby objects clearly ?

(ii) State the range of the power of accommodation of a normal human eye.

OR

(B) Draw a ray diagram to show the correction of eye defect of an old man who can not see an object placed closer than 1 m from his eye, clearly.

(a) A student has difficulty in reading his textbooks but can read the blackboard clearly while sitting in the last row. Name the defect of vision the student is suffering from. List two reasons due to which this defect arises. Write the nature of the lenses required to correct this defect.

OR

(b) Draw a ray diagram to show the path of a ray of light falling obliquely on one of the refracting faces of a triangular glass prism and mark the angle of deviation on it.

(A) Draw a ray diagram to show the refraction of a ray of light passing through an equilateral glass prism. Mark the angle through which the emergent ray bends from the direction of the incident ray and also name it.

OR

(B) Name the type of lenses required by the persons for the correction of their defect of vision called presbyopia. Write the structure of the lenses commonly used for the correction of this defect giving reason for such designs.

(a) Give reasons :

(i) The sky appears dark to passengers flying at very high altitude.

(ii) ‘Danger’ signal lights are red in colour.

OR

(b) What is a rainbow ? “We see a rainbow in the sky only after the rainfall.” Why ?

Draw a ray diagram to show the path of a ray of light which falls obliquely on one of the faces of an equilateral triangular prism made of glass and mark on it the angle of incidence (i) and the angle of deviation (D).

When do we say that a particular person is suffering from hypermetropia ? List two causes of this defect. Name the type of lens used to correct this defect.

A person suffering from presbyopia needs bifocal lens. If he needs two lens of power − 4·0 dioptre and + 2·0 dioptre, which one of these two lenses is for the correction of distant vision and what is its focal length ?

(a) Draw a ray diagram to show the formation of a rainbow in the sky. Mark on the diagram three points A, B and C as given below :

A – where dispersion of light occurs

B – where internal reflection of dispersed light occurs

C – where refraction of dispersed light occurs

OR

(b) Name the muscles present in the human eye which enable it to focus on objects at varied distances (i.e., distant as well as nearby objects). Explain how it happens.

(a) A narrow beam XY of white light is passing through a glass prism ABC as shown in the diagram :

Trace it on your answer sheet and show the path of the emergent beam as observed on the screen PQ.

Name the phenomenon observed and state its cause.

OR

(b) It is observed that the power of an eye to see nearby objects as well as far off objects diminishes with age.

(i) Give reason for the above statement.

(ii) Name the defect that is likely to arise in the eyes in such a condition.

(iii) Draw a labelled ray diagram to show the type of corrective lens used for restoring the vision of such an eye.

(a) When and where does a rainbow appear in the sky ? Draw a labelled ray diagram to show its formation.

OR

(b) What is scattering of light ? Why does the clear sky appear blue ?

(A) Observe the following diagram and answer the questions following it :

(i) Identify the defect of vision shown.

(ii) List its two causes.

(iii) Name the type of lens used for the correction of this defect.

OR

(B) The colour of clear sky from the earth appears blue but from the space it appears black. Why ?

Observe the following diagram showing an image formation in an eye :

(a) Identify the defect of vision shown in the figure.

(b) List its two causes and suggest a suitable corrective lens to overcome this defect.

State the reasons for myopia. With the help of a ray diagram, show the :

(a) Image formation by myopic eye, and

(b) Correction of myopic eye by using an appropriate lens.

What is meant by atmospheric refraction of light ? Explain the following natural phenomenon by using the concept of atmospheric refraction :

(a) Twinkling of stars

(b) Flickering of objects seen through a turbulent stream of hot air

(A) The elderly people, may have both near sightedness and far sightedness. Write the possible solutions, can be proposed for correction of their eye defect.

(B) How does the eye control the amount of light entering into it ?

A person is unable to read a book placed closer than 1 meter from his eyes. Identify the defect of vision in his eyes. Draw the ray diagrams to show the defect of vision and its correction.

What is scattering of light ? How is scattering of light different from reflection of light ? Explain.

Study the given diagram and answer the questions that follow :

(a) Write the name of the eye defect shown in the diagram. Where is the image formed in this eye defect with respect to the retina of the eye ?

(b) List two causes of this eye defect.

(c) With the help of a diagram, show how this eye defect of vision is corrected.

Explain the phenomenon of rainbow formation in the sky. Draw the labelled ray diagram in support of your explanation.

(a) Draw the ray diagram for refraction of light through a glass prism and mark angle of refraction and angle of deviation.

(b) When the path of a light ray refracted through a glass prism is reversed how will the angle of deviation change ? Explain.

What is a rainbow ? Draw a labelled diagram to show its formation.

A person uses lenses of +2.0 D power in his spectacles for the correction of his vision.

(a) Name the defect of vision the person is suffering from.

(b) List two causes of this defect.

(c) Determine the focal length of the lenses used in the spectacles.

Study the diagram given below and answer the questions that follow :

(i) Name the defect of vision represented in the diagram. Give reason for your answer.

(ii) List two causes of this defect.

(iii) With the help of a diagram show how this defect of vision is corrected.

(a) Define the term power of accommodation of human eye. Write the name of the part of eye which plays a major role in the process of accommodation and explain what happens when human eye focuses (i) nearby objects and (ii) distant objects.

OR

(b) Draw a ray diagram to show the formation of a rainbow in the sky. On this diagram mark A – where dispersion of light occurs, B – where internal reflection of light occurs and C – where refraction of light occurs. List two necessary conditions to observe a rainbow.

Name and explain the phenomenon of light due to which the path of a beam of light becomes visible when it enters a smoke filled room through a small hole. Also state the dependence of colour of the light we receive on the size of the particle of the medium through which the beam of light passes.

Define the term power of accommodation of human eye. What happens to the image distance in the eye when we increase the distance of an object from the eye ? Name and explain the role of the part of human eye responsible for it in this case.

(a) Study the diagram given below and answer the questions that follow :

(i) Name the defect of vision depicted in this diagram stating the part of the eye responsible for this condition.

(ii) List two causes of this defect.

(iii) Name the type of lens used to correct this defect and state its role in this case.

OR

(b) What is dispersion of white light ? State its cause. Draw a diagram to show dispersion of a beam of white light by a glass prism.

Draw a ray diagram to show the refraction of a ray of light through a triangular glass prism and mark on it (i) angle of incidence (i), (ii) angle of emergence (e), and (iii) angle of deviation (D). What would happen, if instead of a ray, a beam of white light falls on the prism ? Give reason for the phenomenon that occurs in this case.

Give reasons for the following :

(a) Danger signals installed at airports and at the top of tall buildings are of red colour.

(b) The sky appears dark to the passengers flying at very high altitudes.

(c) The path of a beam of light passing through a colloidal solution is visible.

(a) State one important function of the following parts of the human eye :

(i) Retina

(ii) Pupil

(b) State the role of ciliary muscles in focussing objects at varying distances from the eye.

State reasons for Myopia. With the help of ray diagrams, show the

(a) image formation by a myopic eye, and

(b) correction of myopia using an appropriate lens.

What is Tyndall effect ? Give two examples where this phenomenon is observed. Give reason to explain this phenomenon.

The above image shows a corrective measure for a particular defect of vision.

(i) Identify the defect of vision and state what kind of lens is used to correct this deficiency.

(ii) Draw and label a ray diagram that shows the defect of vision in the above case before correction.

Read the following passage and answer the questions that follow :

Two students, A and B were performing an activity on refraction through glass slab and refraction through prism respectively. Student ‘A’ observed that the emergent light ray is parallel to the direction of incident ray, while student ‘B’ observed that the emergent ray is making a certain angle with respect to the direction of the incident ray in the prism, called angle of deviation. He also noted that the angle of deviation is different for different colours of light.

(a) When white light passes through a glass slab, it does not show dispersion, while it shows dispersion when it passes through a glass prism. Why ?

(b) Why do we get spectrum when white light passes through tiny water droplets present in air ?

(c) (i) For a given pair of mediums, if we change the angle of incidence gradually, will it change the speed of light in that medium ? Explain.

OR

(c) (ii) Calculate the speed of light in a given medium if angle of incidence in air is 60° and angle of refraction in the medium is 30°. Given that speed of light in air is 3 × 10⁸ m/s.

A person allowed a narrow beam of white light from the sun to enter a dark room through a small aperture and placed a glass prism in its path in such a manner that the beam falls on the face AB of the prism as shown in the figure.

A screen S is placed on the other side of the prism, facing AC. On turning the prism slowly, a beautiful band of colours is obtained on the screen. It is the spectrum of sunlight.

(a) Name the phenomenon due to which a prism splits the incident white light into a band of colours.

(b) State the reason of getting a band of seven colours in the above case.

(c) (i) Explain with the help of a labelled ray diagram, an experimental arrangement to show the recombination of the spectrum of white light.

OR

(c) (ii) Draw a labelled ray diagram to show the formation of a rainbow.

The students in a class took a thick sheet of cardboard and made a small hole in its centre. Sunlight was allowed to fall on this small hole and they obtained a narrow beam of white light. A glass prism was taken and this white light was allowed to fall on one of its faces. The prism was turned slowly until the light that comes out of the opposite face of the prism appeared on the nearby screen. They studied this beautiful band of light and concluded that it is a spectrum of white light.

(i) Give any one more instance in which this type of spectrum is observed.

(ii) What happens to white light in the above case?

(iii) (A) List two conditions necessary to observe a rainbow.

OR

(iii) (B) Draw a ray diagram to show the formation of a rainbow. Mark on it, points (a), (b) and (c) as given below :

(a) Where dispersion of light occurs.

(b) Where light gets reflected internally.

(c) Where final refraction occurs.

(a) (i) Define the term power of accommodation of human eye. What happens to the image distance in the eyes when the distance of an object is increased gradually from about 5 m to 500 m from our eyes ? Name and explain the role of the part of human eye responsible for it in this case.

(ii) A person is unable to see distinctly the objects placed beyond 2 m from his eyes. Name the defect of vision the person is suffering from. List two possible causes of this defect and write the type of lenses used for the correction of this defect.

OR

(b) (i) Name and explain the phenomenon of light responsible to make the path of a beam of light visible when it enters a smoke/dust-filled room through a small hole. Also state the dependence of the colour of the light we receive on the size of the particles of the medium through which the light passes.

(ii) A person suffering from presbyopia needs spectacles having bifocal lenses. If the power of two lenses used in his spectacles is + 2·0 D and − 0·5 D, which one of the two lenses is for the correction of his distant vision and what is its focal length ?

Attempt either option A or B.

A.

I. What is meant by accommodation of the human eye?

II. What is the near point of a normal eye and what does it signify?

III. Name which type of lens is used to correct the defect in which a person cannot see distant objects clearly.

IV. Draw a diagram to show how the choice of your lens in (d) helps to see distant objects clearly?

OR

B.

I. What is dispersion of light?

II. Which colour of light deviates the least during dispersion through a prism?

III. State why the sky appears dark to an astronaut in outer space.

IV. Draw a simple labelled diagram to show how white light splits into different colours while passing through a glass prism.

The correct way to connect an ammeter and a voltmeter in an electric circuit is :

1. Ammeter in parallel and voltmeter in series
2. Ammeter and voltmeter both in parallel
3. Ammeter in series and voltmeter in parallel
4. Ammeter and voltmeter both in series

An electric bulb is connected to a power supply of 220 V. If the current drawn by the bulb from the supply is 500 mA, the power of the bulb is :

1. 11 W
2. 110 W
3. 220 W
4. 1100 W

Four identical resistors of 12 Ω each are connected in series to form a square ABCD as shown in the figure. The resistance of the network between the two points 1 and 2 is :

1. 48 Ω
2. 36 Ω
3. 9 Ω
4. 6 Ω

For Questions number 17 to 20, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

Assertion (A) : Nichrome is an alloy which is commonly used in electrical heating devices such as electric irons, toasters, etc.

Reason (R) : The resistivity of nichrome is high and its resistance decreases with increase in temperature.

A wire of length ‘l’ is gradually stretched so that its length increases to 3l. If its original resistance is R, then its new resistance will be :

1. 3R
2. 6R
3. 9R
4. 27R

A piece of wire of resistance ‘R’ is cut lengthwise into three identical parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R′, then the value of R/R′ is :

1. 1/9
2. 1/3
3. 3
4. 9

An electric bulb is rated 220 V; 11W. The resistance of its filament when it glows with a power supply of 220 V is :

1. 4400 Ω
2. 440 Ω
3. 400 Ω
4. 20 Ω

The minimum number of identical bulbs of rating 4V; 6W, that can work safely with desired brightness, when connected in series with a 240 V mains supply is :

1. 20
2. 40
3. 60
4. 80

Which one of the following factors affects the electrical resistivity of a conductor ?

1. Temperature
2. Length
3. Shape
4. Thickness

The maximum resistance of a network of five identical resistors of 15 Ω each can be –

1. 1 Ω
2. 0.5 Ω
3. 0.25 Ω
4. 0.1 Ω

Study the I-V graph for three resistors of resistances R₁, R₂ and R₃ and select the correct statement from the following :

1. R₁ = R₂ = R₃
2. R₁ > R₂ > R₃
3. R₃ > R₂ > R₁
4. R₂ > R₃ > R₁

In case of four wires of same material, the resistance will be minimum if the diameter and length of the wire respectively are

1. D/2 and L/4
2. D/4 and 4L
3. 2D and L
4. 4D and 2L

Consider the following combinations of resistors :

The combinations having equivalent resistance 1 Ω is/are :

1. I and IV
2. Only IV
3. I and II
4. I, II and III

An electric iron of resistance 20 Ω draws a current of 5 A. The heat developed in the iron in 30 seconds is :

1. 15000 J
2. 6000 J
3. 1500 J
4. 3000 J

Assertion (A) : Electrons move from lower potential to higher potential in a conductor.

Reason (R) : A dry cell maintains electric potential difference across the ends of a conductor.

For Questions number 17 to 20, two statements are given one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

When we connect too many electrical appliances to a single socket in a circuit having a fixed value of current rating :

1. the total resistance of the circuit increases.
2. the current drawn from the source decreases.
3. the current increases beyond the rated value.
4. each appliance starts drawing more and more current from the source.

Assertion (A) : The commercial unit of electric energy is kilowatt hour (kWh).

Reason (R) : 1 kWh = 10⁶ joule (J)

For Questions number 17 to 20, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false, but Reason (R) is true.

If four identical resistors, of resistance 8 ohm, are first connected in series so as to give an effective resistance R_s, and then connected in parallel so as to give an effective resistance R_p, then the ratio R_sR_p is

1. 32
2. 2
3. 0.5
4. 16

In the following diagram, the position of the needle is shown on the scale of a voltmeter. The least count of the voltmeter and the reading shown by it respectively are :

1. 0.15 V and 1.6 V
2. 0.05 V and 1.6 V
3. 0.15 V and 1.8 V
4. 0.05 V and 1.8 V

For verifying Ohm’s law, we design an electric circuit diagram in which we show the arrangement of different circuit components. We find that with respect to the resistor, the :

1. ammeter is connected in parallel and the voltmeter in series.
2. ammeter is connected in series and the voltmeter in parallel.
3. ammeter and voltmeter are both connected in series.
4. ammeter and voltmeter are both connected in parallel.

In a resistive circuit if the current is increased to two times, the percentage change in the amount of heat dissipated in the circuit would be :

1. 400%
2. 300%
3. 200%
4. 100%

Two LED bulbs of 12W and 6W are connected in series. If the current through 12W bulb is 0.06A the current through 6W bulb will be :

1. 0.04A
2. 0.06A
3. 0.08A
4. 0.12A

The resistance of a resistor is reduced to half of its initial value. If other parameters of the electrical circuit remain unaltered, the amount of heat produced in the resistor will become :

1. four times
2. two times
3. half
4. one fourth

The expressions that relate (i) Q, I and t and (ii) Q, V and W respectively are (Here the symbols have their usual meanings) :

1. (i) I = Qt   (ii) W = VQ
2. (i) Q = I × t   (ii) W = V × Q
3. (i) Q = It   (ii) V = WQ
4. (i) I = Qt   (ii) Q = VW

An electric kettle consumes 1 kW of electric power when operated at 220 V. The minimum rating of the fuse wire to be used for it is

1. 1 A
2. 2 A
3. 4 A
4. 5 A

A material used for making heating elements of electrical heating devices should have :

1. High resistivity and high melting point.
2. High resistivity and low melting point.
3. Low resistivity and high melting point.
4. Low resistivity and low melting point.

The resistance of a wire does not depend on its :

1. Length
2. Area of cross-section
3. Shape
4. Material

An electrical appliance rated 1000 W is operated at 250 V. What current does it draw?

1. 0.25 A
2. 2.5 A
3. 4.0 A
4. 10 A

(a) Calculate the total resistance of the given circuit and find the total current flowing in it.

OR

(b) How would you join three resistors each of resistance 6 Ω, so that the equivalent resistance of the combination is (i) 9 Ω, and (ii) 4 Ω ?

A bulb consumed 24 J of energy per second, when connected to a 12 V supply. Calculate the power consumed when it is connected to a 6 V supply.

(a) The resistance of a wire of 0.01 cm radius and 1.0 cm length is 7 Ω. Calculate its resistivity.

OR

(b) An electric heater is rated 220 V; 11 A. Calculate the power consumed if the heater is operated at 200 V.

(a) Define volt, the unit of potential difference.

(b) Calculate the work done required to move an electron between two points A and B located at a potential difference of 100 V in an electric field.

(a) A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.

OR

(b) Define electric power. When do we say that the power consumed in an electric circuit is 1 watt ?

An electric kettle is rated 750 W; 220 V. Can this kettle be used in a circuit which has a fuse of current rating 3 A ? Give reason for your answer.

An electric kettle is rated 230 V; 1000 W. Calculate the resistance of its heating element when in operation.

(A) State two applications of Joule’s heating in domestic electric circuit.

(B) (a) Establish the relationship between the commercial unit of electric energy and the SI unit of electric energy.

OR

(b) Determine the total resistance of the parallel combination of three resistances of 2 Ω, 4 Ω and 6 Ω.

(A) Show how you would connect three resistors each of resistance 6 Ω, so that the combination has a resistance of 9 Ω. Also justify your answer.

OR

(B) In the given circuit calculate the power consumed in watts in the resistor of 2 Ω :

Use Ohm’s law to determine the potential difference across the 3 Ω resistor in the circuit shown in the following diagram when key is closed :

Two wires A and B of same material, having same lengths and diameters 0·2 mm and 0·3 mm respectively, are connected one by one in a circuit. Which one of these two wires will offer more resistance to the flow of current in the circuit ? Justify your answer.

An electric source can supply a charge of 500 coulomb. If the current drawn by a device is 25 mA, find the time in which the electric source will be discharged completely.

V – I graph for two conducting wires A and B are as shown. If both wires are of the same length and same diameter, which of the two is made of a material of high resistivity ? Give reasons to justify your answer.

Let the resistance of an electrical device remain constant, while the potential difference across its two ends decreases to one fourth of its initial value. What change will occur in the current through it ? State the law which helps us in solving the above stated question.

(a) An electric heater rated 1100 W operates at 220 V. Calculate (i) its resistance, and (ii) the current drawn by it.

OR

(b) Calculate the equivalent resistance of the following electric circuit :

Attempt either option A or B.

A.

Find out the following in the electric circuit given in the figure-

(i) Effective resistance of two 8 ohm resistors in the combination.

(ii) Current flowing through the 4-ohm resistor

OR

B.

Study the circuit and find out-

(i) Current in 12 ohm resistor

(ii) Difference in the readings of ammeter A₁ and A₂ if any

Attempt either option A or B.

A.

I. State Joule’s Law of heating.

II. What happens to the heat produced in a conductor if the resistance is doubled while keeping other variables constant?

OR

B.

I. Define resistivity.

II. Justify with an example why resistivity is an intrinsic property of a material.

The values of current I flowing in a given resistor for the corresponding values of potential difference V applied across the ends of resistor are given below in the table :

Plot a graph between V and I and calculate the resistance of that resistor.

(a) Name a device which is used to :

(i) Maintain a constant potential difference in a circuit.

(ii) Change the electric current in an electric circuit.

(b) When the potential difference between the terminals of an electric heater is 110 V, a current of 5 A flows through it. What will be the value of current flowing through it when the potential difference is increased to 220 V ?

Consider the given electric circuit :

Calculate the following :

(a) Total resistance of the circuit

(b) The electric current drawn from the battery

(c) Potential difference between points P and Q

(a) Why does an electric bulb become dim when an electric heater in parallel circuit is switched ON ?

(b) How to connect three resistors each of resistance 8 Ω, so that the equivalent resistance of the combination is 12 Ω ? Draw diagram of the combination and justify your answer.

Consider the following electric circuit :

Calculate the values of the following :

(a) The total resistance of the circuit

(b) The total current drawn from the source

(c) Potential difference across the parallel combination of 10 Ω and 15 Ω resistors

(a) Write the relationship between resistivity and resistance of a cylindrical conductor of length l and area of cross-section A. Hence derive the SI unit of resistivity.

(b) Why are alloys used in electrical heating devices ?

Three resistors of 2 Ω, 3 Ω and 6 Ω are connected in (i) series, and (ii) parallel. Draw the arrangements of the resistors and find the equivalent resistance of each arrangement.

The electrical resistivity of three materials A, B and C at 20°C is given below :

(i) Classify these materials as conductor, alloy and insulator.

(ii) Give one example of each of these materials and state one use of each material in the design of an electrical appliance say an electric stove or an electric iron.

The resistance of a wire of 0.01 cm radius is 7 ohms. If the resistivity of the material of the wire is 44 × 10^-6 ohm meter, calculate the length of the wire.

(a) Explain the statement “Potential difference between two points is 1 volt”.

(b) What do the symbols given below represent in an electric circuit ? Write one function of each.

Show the arrangement of three resistors of 2 Ω, 3 Ω and 6 Ω which are connected in such a way that the total/equivalent resistance of the combination is (a) 1 Ω, and (b) 4 Ω. Justify your answer in each case.

(a) State Ohm’s law. Write formula for the equivalent resistance R_p of the parallel combination of three resistors of values R₁, R₂ and R₃.

(b) Find the resistance of the following network of resistors :

In the given circuit when key is closed, determine the following :

(i) Total resistance offered by the three resistors

(ii) Reading of the ammeter

(iii) Reading of the voltmeter

(a) Three resistors R₁, R₂ and R₃ are connected in parallel and the combination is connected to a battery, an ammeter, a voltmeter and a key. Draw suitable circuit diagram to show the arrangement of these circuit components along with the direction of current flowing.

(b) Calculate the equivalent resistance of the following network :

(a) (i) Define Electric Power and write its SI unit. (½ + ½)

(ii) Two bulbs rated 100 W; 220 V and 60 W; 220 V are connected in parallel to an electric mains of 220 V. Find the current drawn by the bulbs from the mains.

OR

(b) (i) State Joule's law of heating. Express it mathematically for the situation when an appliance of resistance R is connected to a source of voltage V and the current I flows through the appliance for a time t.

(ii) A 5 Ω resistor is connected across a battery of 6 volts. Calculate the energy that dissipates as heat in 10 s.

(a) State Ohm's Law. Represent it mathematically.

(b) Define 1 ohm.

(c) What is the resistance of a conductor through which a current of 0.5 A flows when a potential difference of 2 V is applied across its ends ?

(a) List the factors on which the resistance of a uniform cylindrical conductor of a given material depends. (2)

(b) The resistance of a wire of 0.01 cm radius is 10 Ω. If the resistivity of the wire is 50 × 10^-8 Ω m, find the length of this wire. (1)

OR

(a) What is the meaning of electric power of an electrical device ? Write its SI unit. (1½)

(b) An electric kettle of 2kW is used for 2h. Calculate the energy consumed in

(i) kilowatt hour and

(ii) joules. (1½)

An electric motor rated 1100 W is connected to 220 V mains. Find :

(i) The current drawn from the mains,

(ii) Electric energy consumed if the motor is used for 5 hours daily for 6 days.

(iii) Total cost of energy consumed if the rate of one unit is ₹ 5.

OR

Study the following circuit and find :

(i) Effective resistance of the circuit

(ii) Current drawn from the battery

(iii) Potential difference across the 5 Ω resistor

(a) (i) In the following figure, three cylindrical conductors A, B and C are shown along with their lengths and areas of cross-section.

If these three conductors are made of the same material and R_A, R_B and R_C be their respective resistances, then find (I) R_A / R_B, and (II) R_A / R_C.

(ii) If the conductor A is made of copper and the conductor C is made of constantan (alloy of copper and nickel), then which one of the two will have more electrical resistance and why ?

OR

(b) (i) Write the formula for determining the equivalent resistance between A and B of the two combinations (I) and (II) of three resistors R₁, R₂ and R₃ arranged as follows :

(ii) If the equivalent resistance of the arrangements (I) and (II) are R_s and R_p respectively, then which one of the following V – I graphs is correctly labelled ? Justify your answer.

Define the term electric power. An electric device of resistance R when connected across an electric source of voltage V draws a current I. Derive an expression for the power in terms of resistance R and voltage V. What is the power of a device of resistance 400 Ω operating at 200 V ?

A student needs to make a 0.12 Ω resistor. She has some copper wire of 0.80 mm diameter. Resistivity of copper is 1.8 × 10^–8 Ωm

(i) Determine the cross-sectional area of the wire.

(ii) Calculate the length of wire required for the 0.12 Ω resistor.

The figure shows a circuit with a 15 V battery connected to several resistors. Using the given circuit diagram:

A. Find the total current supplied by the battery.

B. Calculate the potential difference between points A and B.

Four cells, a thin wire AB, a voltmeter, an ammeter, a plug key and some thick connecting wires are taken. The circuit is set up as shown below.

The key is inserted into the plug and readings of ammeter (I) and voltmeter (V) are noted. Then the plug key is removed. Now two cells are connected in the circuit in series. Plugging in the key the new values of ‘V’ and ‘I’ are noted. The experiment is repeated by connecting three cells in series and then four cells. In each case ‘V’ and ‘I’ are noted.

(A) Why was the plug key removed after each measurement of ‘V’ and ‘I’ and inserted again for the next step ?

(B) What change takes place in the reading of the voltmeter when a new cell is added in series in the circuit ? Give reason.

(C) In which case will the readings of voltmeter and ammeter be maximum in the above experiment ? What conclusion can be drawn from the straight line graph between ‘V’ and ‘I’ ?

OR

(C) Suppose this experiment is carried out using only one cell but wires of same length & thickness but made of different materials like nichrome wire, fuse wire, copper wire and iron wire which are replaced one by one. Out of V and I which will change and why ?

Read the following passage and answer the questions that follow :

Swati, a class 10 student, observes that when she passes close to the refrigerator in her kitchen, she feels the heat, although the things kept inside the refrigerator are cool.

(a) Describe the cause of heating in the above-mentioned case. [1]

(b) A current I flows through a resistor of resistance R when the potential difference across it is V. Applying Ohm’s law, write the formula for amount of heat produced by the resistor in time t. [1]

(c) (i) Write any two practical applications of heating effect of electric current. [2]

OR

(c) (ii) Define the commercial unit of electric energy and express it in Joules (J). [2]

Three students Shweta, Ayesha and Samridhi were performing an experiment to understand the factors on which the resistance of a conductor depends. Each one of them completed electric circuit with the help of a cell, an ammeter, a plug key and wire.

Shweta put nichrome wire of length ‘l’ in the circuit and after plugging the key, noted current in the ammeter.

Ayesha put nichrome wire of same thickness but twice the length i.e. ‘2l’ in the circuit and after plugging the key, noted current in the ammeter.

Samridhi took copper wire of length ‘l’ and same thickness in the circuit and after plugging the key, noted current in the ammeter.

(a) If the ammeter reading is X ampere with nichrome wire of length ‘l’, then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section ? [1]

(b) What happens to the ammeter reading if the area of cross-section of nichrome wire is doubled, keeping the length of wire ‘l’ the same ? [1]

(c) Define ‘resistivity’. Write its SI unit. Compare the resistivity of an alloy with its constituents metals. [2]

OR

(c) Give reason :

(i) Tungsten is used almost exclusively for making the filament of electric lamps.

(ii) Conductors of bread-toasters are made of an alloy rather than a pure metal. [2]

As shown in the diagram, an electric circuit consisting of an ammeter, a voltmeter, 4 cells of 1·5 V each, a plug key with a gap XY was set up. Voltmeter and ammeter readings were recorded in the observation table for four arrangements as given below :

Arrangement No. 1 – only resistor R₁ in gap XY

Arrangement No. 2 – only resistor R₂ in gap XY

Arrangement No. 3 – Resistors R₁ and R₂ in series in gap XY

Arrangement No. 4 – Resistors R₁ and R₂ in parallel in gap XY

Based on the observations, four V – I graphs A, B, C and D as shown in figure were drawn. Study these graphs.

(a) Which one of the graphs represents the series combination of R₁ and R₂ ?

(b) Which one of these graphs represents the parallel combination of R₁ and R₂ ?

(c) (i) Show an arrangement of three resistors, each of resistance 10 Ω, so that the combination has a resistance of 15 Ω. Give justification for your answer.

OR

(c) (ii) A battery of 6 V is connected with a series combination of five resistors of 0·1 Ω, 0·2 Ω, 0·3 Ω, 0·4 Ω and 0·5 Ω. How much current would flow through the 0·3 Ω resistor ? Justify your answer.

Study the circuit shown in which two resistors X and Y of resistances 3 Ω and 6 Ω respectively are joined in series with a battery of 2 V.

(I) Draw a circuit diagram showing the above two resistors X and Y joined in parallel with same battery and same ammeter and voltmeter.

(II) In which combination of resistors will the (i) potential difference across X and Y and (ii) current through X and Y, be the same ?

(III) (a) Find the current drawn from the battery by the series combination of the two resistors (X and Y).

OR

(III) (b) Determine the equivalent resistance of the parallel combination of the two resistors (X and Y).

In a domestic circuit, six LED bulbs and a ceiling fan are arranged as per the circuit shown in the figure. The source voltage is 220 volts and the power rating of each device is marked in the circuit diagram. Two fuses F₁ and F₂ are also provided in the circuit. Based on the circuit diagram, answer the following questions :

(a) State what happens when

(i) only key K₁ is closed,

(ii) and key K₂ is also closed.

(b) Find the current drawn by the bulb L.

(c) (i) Calculate the resistance of the bulb A. Find the total resistance offered by the circuit to the flow of current when only key K₂ is closed.

OR

(c) (ii) What would happen to the glow of the bulbs in the circuit when K₁ and K₂ both are closed and the fuse F₁ melts suddenly ? Give reason to justify your answer.

When electric current flows in a purely resistive circuit electrical energy gets fully converted into heat energy. The amount of heat produced (H) in the circuit is found to be directly proportional to (i) the square of current (I²) (ii) the resistance (R) of the conductor and (iii) the time (t) for which current flows. In other words H = I²Rt. Electrical devices such an electric fuse, electric heater, electric iron etc. are all based on this effect called heating effect of electric current.

(a) List two properties of heating elements. [1]

(b) List two properties of electric fuse. [1]

(c) Name the principle on which an electric fuse works. Explain how a fuse wire is capable of saving electrical appliances from getting damaged due to accidently produced high currents. [2]

OR

(c) The power of an electric heater is 1100 W. If the potential difference between the two terminals of the heater is 220 V, find the current flowing in the circuit. What will happen to an electric fuse of rating 5 A connected in this circuit ? [2]

In a domestic circuit five LED bulbs are arranged as shown. The source voltage is 220 V and the power rating of each bulb is marked in the circuit diagram. Based on the following circuit diagram, answer the following questions :

(a) State what happens when (i) key K₁ is closed. (ii) key K₂ is closed. [1]

(b) Find the current drawn by the bulb B when it glows. [1]

(c) Calculate (i) the resistance of bulb B, and (ii) total resistance of the combination of four bulbs B, C, D and E. [2]

OR

(c) What would happen to the glow of all the bulbs in the circuit when keys K₁ and K₂ both are closed and the bulb C suddenly get fused ? Give reason to justify your answer. [2]

Study the following circuit :

On the basis of this circuit, answer the following questions :

(a) Find the value of total resistance between the points A and B. [1]

(b) Find the resistance between the points B and C. [1]

(c) (i) Calculate the current drawn from the battery, when the key is closed. [2]

OR

(c) (ii) In the above circuit, the 16 Ω resistor or the parallel combination of two resistors of 8 Ω, which one of the two will have more potential difference across its two ends ? Justify your answer. [2]

Consider the following electrical circuit diagram in which nine identical resistors of 3 Ω each are connected as shown. If the reading of the ammeter A₁ is 1 ampere, answer the following questions :

(a) What is the relationship between the readings of A₁ and A₃ ? Give reasons for your answer. [1]

(b) What is the relationship between the readings of A₂ and A₃ ? [1]

(c) Determine the reading of the voltmeter V₁. [2]

OR

(c) Find the total resistance of the circuit. [2]

Study the following electric circuit in which the resistors are arranged in three arms A, B and C :

(a) Find the equivalent resistance of arm A. (1)

(b) Calculate the equivalent resistance of the parallel combination of the arms B and C. (1)

(c) (i) Determine the current that flows through the ammeter. (2)

OR

(ii) Determine the current that flows in the ammeter when the arm B is withdrawn from the circuit. (2)

(a) A smart home uses energy monitoring system to track electricity usage of appliances. In a month of 30 days, the following devices are used :

1. An electric heater of 1500 W used for 4 hours daily.

2. A microwave oven rated at 1·5 kW used for 3 hours daily.

(i) Define electric power and write its SI unit.

(ii) Calculate the total energy consumed in joules and kWh in a whole month.

(iii) Find out the total cost of electricity for running both appliances for a month of 30 days if the cost of 1 unit is ₹ 7.

OR

(b) (i) What is meant by electrical resistivity of a material ?

(ii) A series electric circuit comprising a resistor made of a metallic wire has an ammeter which reads 300 mA. If the length of the wire is made three times, what will be the new reading in the ammeter ?

(iii) Calculate the resistance of a 500 m long aluminium wire of cross-sectional area 1 × 10^-3 m² and resistivity 2·65 × 10^-8 Ω m.

(a) (i) Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why ?

(ii) Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why ?

(iii) Define the S.I. unit of electric current.

OR

(b) (i) How many bulbs of resistance 8 Ω each should be connected in parallel combination to draw a current of 2 A from a battery of 4 V ?

(ii) Name the device used for measuring electric current. How is it connected in a circuit ?

(iii) State Joule’s law of heating.