PRACTICE QUESTIONS
1. Define principle focus of a concave mirror?
2. Name a mirror that can give an erect and enlarged image of an
object?
3. Why do we prefer a convex mirror as a rear-view mirror in
vehicles?
4. An object ,6cm in size ,is placed at 30 cm in front of a concave
mirror of focal length 15 cm .At what distance from the mirror
should a screen be placed in order to obtain a sharp image? Find
the nature and size of the image.
5. A concave mirror produces four times magnified real image of
object placed at 15 cm in front of it .Where is the image located?
6. A ray of light travelling in air enters obliquely into water .Does the
light ray bend towards the normal or away from the normal? Why?
7. A concave lens has focal length of 20 cm. At what distance should
the object from the lens be placed so that it forms an image at 10
cm from the lens? Also, find the magnification produced by the
lens.
8. A convex lens forms a real and inverted image of a needle at a
distance of 50 cm from it .Where is the needle placed in front of
the convex lens if the image is equal to the size of the object? Also,
find the power of the lens.
9. One–half of a convex lens is covered with a black paper .Will this
lens produce a complete image of the object?
10. A converging lens of focal length 20 cm forms an image 10 cm
from the lens .How far is the object placed from the lens? Draw the
ray diagram.
11. Name the type of mirror used in the following situations.
(a) Headlights of a car.
(b) Side /rear- view mirror of a vehicles
(c) Solar furnace.
12. A doctor has prescribed a corrective lens of power +1.5D .Find the
focal length of the lens .Is the prescribed lens diverging or
converging?
13. The magnification produced by a plane mirror is +1 .What does this
mean?
14. Light enters from air to glass having refractive index 1.50 .What is
the speed of light in the glass?
15. Define 1 dioptre of power of a lens.
16. Define Snell’s law?
17. When light enters the atmosphere it strikes on extremely fine
particles, which deflect the rays of light in all possible directions, This
is due to
a) reflection of light
b) atmospheric refraction
c) scattering of light
d) dispersion of light
18. An object is placed in front of a convex mirror. Its image is formed
a) at a distance equal to the object distance in front of the mirror.
b) at twice the distance of the object in front of the mirror.
c) half the distance of the object in front of the mirror.
d) behind the mirror and it’s position varies according to the object
distance
19. The refractive indices of three media are given below:
Medium Refractive index
A 1.6
B 1.8
C 1.5
A ray of light is travelling from A to B and another ray is travelling
from B to C.
(a) In which of the two cases the refracted ray bends towards the
normal?
In which case does the speed of light increase in the second medium?
Give reasons for your answer.
20. (i) Explain why the refractive index of any material with respect to
air is always greater 1.
(ii)In the figure below a light ray travels from air into the semi-
circular plastic block. Give a reason why the ray does not deviate
at the semi-circular boundary of the plastic block.
Complete the ray diagram of the above scenario when the light ray
comes out of the plastic block from the top flat end.
21. A 10 cm long pencil is placed 5 cm in front of a concave mirror having
a radius of curvature of 40 cm.
(i) Determine the position of the image formed by this mirror.
(ii) What is the size of the image?
Draw a ray diagram to show the formation of the image as
mentioned in the part (i).
