EXER CISES
1. Which one of the following materials cannot be used to make a lens?
(a)Water
(b)Glass
(c)Plastic
(d) Clay

Ans:-(d) Clay

2. The image formed by a concave mirror is observed to be virtual, erect and larger
than the object. Where should be the position of the object?
(a)Between the principal focus and the centre of curvature
(b)At the centre of curvature
(c)Beyond the centre of curvature
(d)Between the pole of the mirror and its principal focus.

Ans:-(d)Between the pole of the mirror and its principal focus.

3. Where should an object be placed in front of a convex lens to get a real image of the
size of the object?

(a)At the principal focus of the lens
(b)At twice the focal length
(c)At infinity
(d)Between the optical centre of the lens and its principal focus.

Ans:-(b)At twice the focal length

4. A spherical mirror and a thin spherical lens have each a focal length of-15 cm. The
mirror and the lens are likely to be
(a)both concave.
(b)both convex.

(c)the mirror Is concave and the lens is convex.
(d)the mirror Is convex, but the lens is concave.

Ans:-(a)both concave.

5. No matter how far you stand from a mirror, your image appears erect. The mirror
is likely to be
(a)plane.
(b)concave
(c)convex
(d)either plane or convex

Ans:-(d)either plane or convex

6. Which of the following lenses would you prefer to use while reading small letters
found in a dictionary?
(a)A convex lens of focal length 50 cm.
(b)A concave lens of focal length 50 cm.

(c)A convex lens of focal length 5 cm.
(d)A concave lens of focal length 5 cm.

Ans:-(c)A convex lens of focal length 5 cm.

7. We wish to obtain an erect image of an object, using a concave mirror of focal
length 15 cm. What should be the range of distance of the object from the mirror?
What is the nature of the Image? Is the image larger or smaller than the object?
Draw a ray diagram to show the image formation in this case.

Ans.: In a concave mirror, an erect image is obtained only when the object is held between the pole and the principal focus of the mirror. So, the range of distance of the object from the mirror is 15cm.
The image should be erect and virtual. The image is larger than the object.

8. Name the type of mirror used in the following situations.
(b) Side/rear-view mirror of a vehicle.
(c)Solar furnace.

Ans. : (a) A concave mirror is used for the headlights of a car. The light source is should be placed at the focus of the mirror.
(b) As a side rare view mirror of a vehicle, a convex mirror is used.
(c) For solar furnace, a concave mirror is used. 9. One-half of a convex lens Is covered with a black paper. Will this lens produce a
observations.
10. An object 5 cm in length is held 25 cm away from a converging lens of focal length
10 cm. Draw the ray diagram and find the position, size and the nature of the
11. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far
is the object placed from the lens? Draw the ray diagram.
12. An object is placed at a distance of 10 cm from a convex mirror of focal length
15 cm. Find the position and nature of the image.
13. The magnification produced by a plane mirror is +1. What does this mean?
14. An object 5.0 cm In length is placed at a distance of 20 cm in front of a convex
mirror of radius of curvature 30 cm. Find the position of the image, its nature
15. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal
length 18 cm. At what distance frem the ma ror should a screen be placed, so that
a sharp focused image can be obtained? Find the size and the nature of the image.
16. Find the focal length of a lens of power- 2.0 D, What type of lens is this?
17. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of
the lens. Is the prescribed lens diverging or converging?