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#### Light Important Questions

8th Standard EM

Reg.No. :
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Science

Time : 01:00:00 Hrs
Total Marks : 50
6 x 1 = 6
1. Mirrors having a curved reflecting surface are called as

(a)

plane mirrors

(b)

spherical mirrors

(c)

simple mirrors

(d)

None of the above

2. The centre of a sphere of which the reflecting surface of a spherical mirror is a part is called

(a)

pole

(b)

centre of curvature

(c)

(d)

aperture

3. The distance from the pole to the focus is called

(a)

Pole length

(b)

focal length

(c)

principal axis

(d)

None of the above

4. If the focal length of a spherical mirror is 10 cm, what is the value of its radius of curvature?

(a)

10 cm

(b)

5 cm

(c)

20 cm

(d)

15 cm

5. The refractive index of water is

(a)

1.0

(b)

1.33

(c)

1.44

(d)

1.52

6. In which mirror the following statement is labeled?

(a)

Convex mirror

(b)

Concave mirror

(c)

Plane mirror

(d)

Spherical mirror

7. 4 x 1 = 4
8. Nature of the images formed by a convex mirror is _________.

()

Virtual and erect

9. It the angle of incidence is 45°, then the angle of reflection is ______.

()

45°

10. Two mirrors are parallel to each other, then the number of images formed is ________.

()

11. __________ is the best reflector of light

()

Silver

12. 5 x 1 = 5
13. Convex mirror

14. (1)

Bending of light

15. Regular reflection

16. (2)

plane mirror

17. Snell’s law

18. (3)

sin i /sin r = μ

19. Refractive index

20. (4)

rear - view mirror

21. Refraction

22. (5)

c / v = μ

1 x 2 = 2
23. Assertion (A): The pencil appears, to be bent when we see it through the glass of water.
Reason (R): Lightray travels from a denser medium to a rarer medium, it has deviated from its straight-line path.
a) If both assertion and reason are true and reason is the correct explanation of the assertion.
b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
c) Assertion is true but the reason is false.
d) Assertion is false, but the reason is true.

24. 3 x 2 = 6
25. Curved mirrors produce images that are either enlarged or diminished.

26. In dispersion, the violet-colored light has a' long wavelength and is deviated more.

27. Principal focus is also known as focal point.

28. 4 x 2 = 8
29. The radius of curvature of a spherical mirror is 20 cm. Find its focal length.

30. If two plane mirrors are inclined to each other at an angle of 90°, find the number of images formed.

31. Who founded the Book "On Burning Mirrors"?

32. What is the value of velocity of light in air?

33. 3 x 3 = 9
34. What is called a spherical mirror?

35. Define focal length?

36. State the laws of reflection.

37. 2 x 5 = 10
38. What is reflection? Write short notes on regular and irregular reflection?

39. What is dispersion? Explain in detail.