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Class 10 Light-Reflection and Refraction extra questions

## Chapter 10 : Light-Reflection and Refraction

### Topic 1: Reflection of Light and Plane and Spherical Mirrors

#### Very Short Answer Type Questions [1 Mark]

Q.1. What is light?

Ans. The form of energy which provides us with the sensation of sight is known as light.

Q.2. Name a metal, which is the best reflector of light.

Ans. Silver (Ag).

Q.3. Why do we see our image in a shining spoon?

Ans. Because the shining surface of spoon behaves like a curved mirror.

Q.4. What is meant by angle of incidence?

Ans. The angle between the incident ray and normal to the mirror is called the angle of incidence.

Q.5. What is the angle of incidence when a ray falls normally on a mirror?

Ans. The angle of incidence, ∠i = 0°.

Q.6. What is meant by angle of reflection?

Ans. The angle between the reflected ray and normal to the mirror is, known as the angle of reflection.

Q.7. What is the angle of reflection when a ray falls normally on a mirror?

Ans. The angle of reflection, ∠r = 0°.

Q.8. What is the value of the focal length of a plane mirror?

Ans. The focal length of the plane mirror is infinite.

Q.9. Define the real image of an object.

Ans. When rays of light starting from a point P, after reflection from a mirror, meet actually at another point Q, then the point Q is called the real image of the point P. A real image can be formed on a screen.

Q.10. What is a virtual image of an object?

Ans. When rays of light starting from a point P, after reflection from the mirror, appear to come from another point Q, then the point Q is called the virtual image of the point P. A virtual image cannot be formed on the screen.

Q.11. What is an opaque substance?

Ans. A substance which does not allow light to pass through it is known as opaque material.

Q.12. Calculate the angle of reflection from the given ray diagram.

Ans. Angle of incidence = 90° – 30° (According to given diagram) ∠i = 60° According to law of reflection ∠i = ∠r Thus, angle of reflection ∠r = 60°

Q.13. If an object is placed at a distance of 10 cm in front of a plane mirror, how far would it be from its image?

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

Q.14. If an object is placed at a distance 25 cm in front of a plane mirror, how far would it be from its image?

Ans. 50 cm

Q.15. The image seen in the plane mirror cannot be formed on a screen. What name is given to this type of image?

Ans. Virtual image

Q.16. Name the phenomenon responsible for the following effect. If we stand in front of the plane mirror and we lift our right hand, then our image lifts its left hand.

Ans. Lateral inversion.

Q.17. The letter F is placed in front of a plane mirror, how would its image look like

Ans.

Q.18. A ray incident normally on a plane mirror, retraces its path on reflection. Why?

Ans. A ray incident normally on a mirror falls along the normal to mirror. Thus, angle of incidence, i = 0°. As the angle of reflection (r) = angle of incidence, thus, reflected ray goes along the normal. Hence, the ray retraces its path.

Q.19. Name two types of the spherical mirror.

Ans. (i) Concave mirror (ii) Convex mirror

Q.20. Which of the two mirrors is diverging, concave or convex?

Ans. A convex mirror is diverging.

Q.21. What is the focal length?

Ans. The focal length is the distance between the pole and focuses in a spherical mirror.

Q.22. Out of convex mirror and concave mirror, whose focus is situated behind the mirror?

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

Q.23. What happens when the rays of the sun are focused at a point on the paper by using a concave mirror?

Ans. Paper starts burning because concave mirror concentrates sunlight at a point on the paper.

Q.24. Define the principal axis of a spherical mirror.

Ans. It is a straight line passing through the pole (P) and centre of curvature (C) of the spherical mirror.

Q.25. Name a mirror which is converging.

Ans. Concave mirror.

Q.26. What is the radius of curvature of a spherical mirror?

Ans. The radius of curvature of a spherical mirror is the radius of a hollow sphere of glass, of which the spherical mirror is part, i.e., it is the distance between pole (P) and centre of curvature (C).

Q.27. What do you mean by the pole of a spherical mirror?

Ans. The pole of a spherical mirror is the centre of the mirror.

Q.28. What is the centre of curvature of a spherical mirror?

Ans. It is the centre of the hollow sphere of which the spherical mirror is a part.

Q.29. A ray of light passing through the centre of curvature of a concave mirror retraces its path on reflection why?

Ans. Because such a ray falls normally on mirror. Thus ∠ i = 0, ∠ r = ∠ i = 0.

Q.30. What is the relationship between the angle of incidence (∠ i) and the angle of refraction (∠ r)?

Ans. The value of the angle of incidence ∠ i is equal to the angle of reflection, ∠ r, i.e., ∠ i = ∠ r.

Q.31. What is the relation between focal length and radius of curvature of the concave mirror? Does the same relation hold for a convex mirror?

Ans. f = R/2 . Yes, the same relation holds true for a convex mirror.

Q.32. A ray of light moving along a principal axis is falling on a concave mirror. In which direction it is reflected?

Ans. It is reflected back along the principal axis of the mirror because here ∠ r = ∠ i = 0.

Q.33. What are the angle of incidence, when a ray of light falls and the spherical mirror from its centre of curvature?

Ans. The angle of incidence is zero.

Q.34. The focal length of a concave mirror is 25 cm. What is its radius of curvature?

Ans. Focal length = R /2 ∴ R = 2f = 2 × 25 = 50 cm

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