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#### Light Book Back Questions

9th Standard

Reg.No. :
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Science

Time : 00:45:00 Hrs
Total Marks : 30
3 x 1 = 3
1. The focal length of a concave mirror is 5cm. Its radius of curvature is

(a)

5 cm

(b)

10 cm

(c)

2.5 cm

2. The speed of light is maximum in

(a)

vacuum

(b)

glass

(c)

diamond

3. Which of the following statements about total internal reflection is true?

(a)

angle of incidence should be greater than critical angle

(b)

light must travel from a medium of higher refractive index to a medium of lower refractive index

(c)

both (a) and (b)

4. 3 x 1 = 3
5. A spherical mirror whose reflecting surface is curved outwards is called ___________ mirror

()

10 cm

6. All distances parallel to the principal axis are measured from the ____________ of the mirror

()

pole

7. Light is refracted or bent while going from one medium to another because its __________ changes

()

velocity

8. 4 x 1 = 4
9. If a ray of light passes obliquely from one medium to another, it does not suffer any deviation.

(a) True
(b) False
10. An object is placed at distance of 3 cm from a plane mirror. The distance of the object and image is 3 cm.

(a) True
(b) False
11. The distance from centre of curvature of the mirror to the pole is called the focal length of the mirror.

(a) True
(b) False
12. When an object is at the centre of curvature of concave mirror the image formed will be virtual and erect.

(a) True
(b) False
13. 3 x 2 = 6
14. Light travels from a rarer medium to a denser medium. Th e angles of incidence and refraction are respectively 45o and 30o. Calculate the refractive index of the second medium with respect to the first medium.
Angle of incidence i = 45o
Angle of refraction r = 30o

15. A coin in a glass beaker appears to rise as the beaker is slowly filled with water, why?

16. Why does a ray of light bend when it travels from one medium to another?

17. 3 x 3 = 9
18. An object 2 cm high is placed at a distance of 16 cm from a concave mirror which produces a real image 3 cm high. Find the position of the image.

19. State the direction of incident ray which after reflection from a spherical mirror retraces its path. Give reason for your answer.

20. Write the spherical mirror formula and explain the meaning of each symbol used in it.

21. 1 x 5 = 5
22. Find the size, nature and position of image formed when an object of size 1 cm is placed at a distance of 15 cm from a concave mirror of focal length 10 cm.