Class 10 Science · Chapter 9

Light - Reflection and Refraction

409 Class 10 Science questions on Light - Reflection and Refraction from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.

NCERT exercises

Exercises (17) Intext Questions (Page 142) (4) Intext Questions (Page 145) (2) Intext Questions (Page 150) (5) Intext Questions (Page 158) (3)

NCERT Exemplar exercises

Multiple Choice Questions (19) Short Answer Questions (10) Long Answer Questions (9)

CBSE Class 10 Science previous year papers, with answers →

Questions · page 21 of 21

Q401 CBSE 2017
The correct sequencing of angle of incidence, angle of emergence, angle of refraction and lateral displacement shown in the following diagram by digits 1, 2, 3 and 4 is :
1. (a)2, 4, 1, 3
2. (b)2, 1, 4, 3
3. (c)1, 2, 4, 3
4. (d)2, 1, 3, 4
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(b) 2, 1, 4, 3

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Q402 CBSE 2017
When you focus the image of a distant flag, whose shape is given below, on a screen using a convex lens, the shape of the image as it appears on the screen is
1. (a)A flag with its base at the top and its cloth at the bottom, extending to the left of the pole
2. (b)A flag with its base at the top and its cloth at the bottom, extending to the right of the pole
3. (c)A flag with its base at the bottom and its cloth at the top, extending to the right of the pole
4. (d)A flag with its base at the bottom and its cloth at the top, extending to the left of the pole
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(a) A flag with its base at the top and its cloth at the bottom, extending to the left of the pole

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Q403 CBSE 2017

Study the following ray diagram and state any two mistakes committed by the student while tracing it. Rectify these mistakes and draw the correct ray diagram to show the real position of the image corresponding to the position of the object.

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The foci were unequally spaced and a ray missed O; correctly drawn, the image is real, inverted, enlarged and beyond $2 F_{2}$ .
Mistakes (any two): (i) The foci are marked at unequal distances: $F_{2}$ is nearer the lens than $F_{1}$ , and $2 F_{1}$ and $2 F_{2}$ are not at equal distances either; both foci of a lens lie at the same distance $f$ from the optical centre. (ii) The ray drawn towards the optical centre does not pass through $O$ : it crosses the principal axis to the right of $O$ , whereas a ray through $O$ goes straight on. (iii) The image is shown between $F_{2}$ and $2 F_{2}$ and smaller than the object; for an object between $F_{1}$ and $2 F_{1}$ it must be beyond $2 F_{2}$ and enlarged. Correct ray diagram (see the figure): with $O F_{1} = O F_{2} = f$ , the ray parallel to the axis passes through $F_{2}$ after refraction and the ray through $O$ goes undeviated; they meet beyond $2 F_{2}$ , where the image is real, inverted and enlarged.

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Q404 CBSE 2017
A student determined the focal length of a convex lens as $20$ cm. He then obtained the image of an object using this lens. The image formed was inverted, equal in size and real.
1. (i)What is the position of the object in front of convex lens ?
2. (ii)What will be the position of image formed ? Draw ray diagram to justify your answer.
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The object is at $2 F_{1}$ , 40 cm from the lens, and the real, inverted, same-size image forms at $2 F_{2}$ , 40 cm behind it.
(i) The object is at $2 F_{1}$ , that is $40$ cm in front of the lens ( $u = - 40$ cm). (ii) The image forms at $2 F_{2}$ , $40$ cm behind the lens on the other side ( $v = + 40$ cm); it is real, inverted and of the same size, and the ray diagram shows the two rays meeting there.

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Q405 CBSE 2017
A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that he gradually moves the flame towards the lens and each time focuses the image on the screen.
1. (a)In which direction-toward or away from the lens, does he move the screen to focus the image ?
2. (b)How does the size of the image change ?
3. (c)How does the intensity of the image change as the flame moves towards the lens ?
4. (d)Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size ?
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The screen moves away, the image becomes larger and dimmer, and a same-size inverted image forms with the flame at 20 cm ( $2 F$ ).
(a) Away from the lens: as the flame comes in from 60 cm the image distance grows (12 cm, 15 cm, 20 cm and 30 cm for the flame at 60 cm, 30 cm, 20 cm and 15 cm). (b) The image becomes larger: the magnification changes from $- 0.2$ through $- 1$ to $- 2$ . (c) The intensity (brightness) of the image decreases: the image grows faster than the light the lens collects from the nearer flame, so the image becomes dimmer. (d) At about 20 cm, that is at 2F, twice the focal length; the inverted image of the same size is then also 20 cm from the lens.

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Q406 CBSE 2017

Trace the path of a ray of light incident at an angle of $4 5^{\circ}$ on a rectangular glass slab. Write the measure of the angle of refraction, the angle of emergence and the lateral displacement suffered by the ray as it passes through the slab.

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$r \approx 2 8^{\circ}$ , $e = 4 5^{\circ}$ and the lateral displacement is about $0.33 t$ (1.6 cm for a 5 cm thick slab).
Angle of refraction $r \approx 2 8^{\circ}$ (for glass of refractive index about 1.5). Angle of emergence $e = 4 5^{\circ}$ , equal to the angle of incidence: the emergent ray is parallel to the incident ray. Lateral displacement, the perpendicular distance between the emergent ray and the incident ray produced: about a third of the slab's thickness, $d = \frac{t sin ( i - r )}{cos r} \approx 0.33 t$ — about 1.6 cm for a slab 5 cm thick.

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Q407 CBSE 2017

A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that he moves gradually the flame towards the lens and each time focuses its image on the screen. (A) In which direction does he move the lens to focus the flame on the screen ? (B) What happens to the size of the image of the flame formed on the screen ? (C) What difference is seen in the intensity (brightness) of the image of the flame on the screen ? (D) What is seen on the screen when the flame is very close (at about 5 cm) to the lens ?

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The lens moves away from the screen; the image grows larger and dimmer; at 5 cm no image forms on the screen.
(A) He moves the lens away from the screen (towards the flame), because the image distance increases as the flame comes nearer. (B) The image of the flame becomes larger (and stays inverted). (C) The image becomes less bright (dimmer), because the light is spread over a bigger image. (D) No image of the flame is formed on the screen, at most a faint patch of light: with the flame inside the focal length the lens forms a virtual, erect, magnified image on the same side as the flame, which cannot be caught on a screen.

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Q408 CBSE 2017
Using a convex lens a student has focused a very small sized image of a candle flame on a screen. If keeping the position of the lens fixed he gradually, in steps, shift the candle towards the lens, then every time
1. (i)in which direction he will have to move the screen in order to have distinct image on it ?
2. (ii)How would the size of the image change ? Will the intensity of the image increase or decrease ?
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The screen is moved away from the lens; the image gets larger and its intensity decreases.
(i) Away from the lens: each time the candle is brought nearer (while it stays beyond the focus), the image forms farther from the lens, so the screen has to be moved away from the lens. (ii) The image becomes larger each time (it stays real and inverted). Its intensity decreases: the image grows faster than the light the lens collects, so the light is spread more thinly over it.

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Q409 CBSE 2017

An object of height 2.0 cm is placed on the principal axis of a convex lens of focal length 10 cm. The distance of the object from the optical centre (O) of the lens is 20 cm. Choose a proper scale and draw a ray diagram to find the position, nature and size of the image. Also measure and write the size of the image and its distance from the optical centre of the lens.

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The image is real, inverted and 2.0 cm tall (same size), formed 20 cm from the lens at $2 F_{2}$ .
Position: at $2 F_{2}$ , $20$ cm from the optical centre on the other side of the lens ( $v = + 20$ cm). Nature: real and inverted. Size: the same as the object, $2.0$ cm ( $h^{'} = - 2.0$ cm, the minus sign showing that it is inverted). On a scale drawing of $1$ cm $= 2.5$ cm the image is measured $8$ cm from O and $0.8$ cm tall, which is $20$ cm and $2.0$ cm.

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