CBSE I NCERT Chapter -Light _Refraction and Refraction solved Questions

VERY SHORT QUESTIONS CARRYING 1 MARK EACH.

1. Out of convex mirror and concave mirror, whose focus is situated behind the mirror?

Ans: The focus of convex mirror is situated behind it.

2. For what position of an object, a concave mirror forms an enlarged virtual image?

Ans: Object between pole (P) and focus (F) of the concave mirror.

3. If the focal length of a concave mirror is 25cm. What is its radius of curvature?

Ans: Focal length = Radius of curvature / 2

25 = R / 2 => R = 50cm.

4. A ray of light falls on a mirror normally. What are the values of angle of incidence andthe angle of reflection?

Ans: Both angle of incidence and the angle of reflection are zero.

5. What is the focal length of a plane mirror?

Ans: Infinite.

6. Which spherical mirror is called a divergent mirror?

Ans: A convex mirror is called a divergent mirror.

7. What is the angle of incidence, when a ray of light falls on the spherical mirror from itscentre of curvature?

Ans: The angle of incidence is zero, when a ray of light falls on the spherical mirror from its centre of curvature.

8. Name the type of mirror that always forms a virtual image for a real object?

Ans: Convex Mirror.

9. State the relation between radius of curvature and focal length of spherical mirrors.

Ans: Radius of curvature = 2 X focal length.

R = 2f.

10. Which of the two is a diverging lens? Convex lens (or) Concave lens.

Ans: Concave lens.

11. If an object is placed at a distance of 10cm in front of a plane mirror, how far would it be from its image?

Ans: The object would be at a distance of 20cm from its image.

12. Name the physical quantity which remains the same when light goes from one medium to another?Ans: Frequency of light.

13. Define power of a lens.

Ans: The reciprocal of the focal length of the lens is called power of a lens. P = 1/f

14. Calculate the power of a convex lens of focal length 25cm?

Ans: Focal length f = 25cm.

Power = 1/.25 = 100/25 = +4D.

15. Name the phenomenon responsible for the following affect.

When we sit in front of a plane mirror and write with our right hand, it appears in the mirror that we are writing with the left hand.

Ans: Lateral Inversion.

16. Define Refractive Index:

Ans: It is the ratio of speed of light in vacuum to the speed of light in medium is called Refractive index.

17. Why is the convex lens also known as a converging lens?

Ans: A convex lens is also known as a converging lens because it converges a parallel beam of light raying passing through it.

18. Give the ratio of velocities of two light waves travelling is vacuum and having wave lengths 4000A0 and 8000A0.

Ans: In Vacuum, light of all the wave lengths travel with the same velocity i.e. 3 X 108 m/sec.

19. For what angle of incidence, the lateral shift produced by parallel sided glass plate is zero?

Ans: For i = 0.

20. What are the factors on which the lateral shift depends?

Ans: Thickness of the refracting medium, angle of incidence and its refractive index.

21. What is the power of a plane glass plate?

Ans: Zero.

22. An object is placed at the focus of a concave lens. Where will its image be formed?

Ans: The rays will appear to come from infinity. Therefore, a virtual image will be formed at infinity.

23. What is the unit of power of a lens?

Ans: Dioptre.

24. Refractive index of media A,B,C and D are

A 1.54

B 1.33

C 1.46

D 1.62

In which of the four media is the speed of light (i) Minimum (ii) Maximum.

Ans: (i) Speed of light is minimum in medium D (n = 1.62).

(ii) Speed of light is maximum is medium B (n = 1.33).

25. Why the stars appear to twinkle?

Ans: The twinkling of a star is due to the atmospheric refraction of star’s light.

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