Railway Science (Physics-Light and Optics)

Total Questions: 50

31. The value of absolute refractive index of a medium is always _________. [RRC Group D 24/08/2022 (Afternoon)]

Correct Answer: (b) more than 1
Solution:More than 1. Refractive index of a medium is always greater than or equal to 1 because the definition of refractive index, n of a medium is the ratio of the speed of light in a vacuum, c, to the speed of light in the medium, v. i.e. n = c/v. Refractive index below 1 means a speed above the speed of light in vacuum, which is not possible in real life. The refractive index of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium described by Snell's law of refraction.

32. A ray of light is incident on the pole of a concave mirror. What is the acute angle formed between the incident ray and the principal axis called? [RRC Group D 24/08/2022 (Afternoon)]

Correct Answer: (d) angle of incidence
Solution:

angle of incidence. Terminologies : Centre of curvature (C) - Centre of the sphere of which the mirror is a part. Radius of curvature (R) - Radius of the sphere of which the mirror is a part. Pole - Geometric centre of the spherical surface of the mirror. Principal axis - Straight line joining the pole of the mirror to its centre of curvature.

33. Virtual and erect images are always formed by which of the following mirrors? [RRC Group D 24/08/2022 (Afternoon)]

(A) convex mirror (B) plane mirror (C) concave mirror

Correct Answer: (c) Both A and B
Solution:

Both A and B. A spherical mirror is a mirror that has the shape of a piece cut out of a spherical surface.

34. A beam of white light is refracted through a triangular glass prism to produce a palette of seven colours. Which of these statements is correct? [RRC Group D 24/08/2022 (Afternoon)]

(i) The red color component has a minimum refractive index.
(ii) The deviation of violet color component is minimum.
(iii) All components of white light have the same speed in glass.

Correct Answer: (a) only (i)
Solution:

only (i). The phenomenon due to which white light splits into seven colours on passing through a prism is called dispersion. White light is made up of seven bands of colours each having different wavelengths. Upon passing through a medium, each of the colors travels at different speeds and hence has different angles of refraction leading to the splitting of the light. The violet light is deviated more than the red light because the refractive index of the prism for violet rays of light is more.

35. The laws of reflection hold true for which of the following mirror(s)? [RRC Group D 24/08/2022 (Evening)]

(A) Concave mirror (B) Convex mirror (C) Plane mirror

Correct Answer: (b) A, B and C
Solution:

A, B and C. According to the laws of reflection, The angle of incidence is equal to the angle of reflection, and The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane

36. concave mirror forms a real, inverted and diminished image of an object. Where is the object placed? [RRC Group D 25/08/2022 (Morning)]

Correct Answer: (b) Beyond centre of curvature
Solution:

Beyond the centre of curvature. Concave mirrors form both real and virtual images.

37. A ray of light bends towards the normal while traveling from medium A to medium B. Which of the following statements is/are correct? [RRC Group D 25/08/2022 (Afternoon)]

(A) Medium A is optically denser than medium B.
(B) Speed of light is more in medium A than medium B.
(C) Refractive index of medium B is more than the refractive index of medium A.

Correct Answer: (d) Both B and C
Solution:

Both B and C. It is a phenomenon of refraction. It happens with sound, water and other waves. Because the rarer the medium, the faster the speed of light, when light enters from rarer to denser medium, the speed decreases and hence the light takes a short path by bending towards the normal to reach the boundary in the same time.

38. Which of the following optical devices can be used to produce a parallel beam of rays from a point source of light? [RRC Group D 25/08/2022 (Evening)]

(A) Convex lens          (B) Concave lens

(C) Concave mirror   (D) Convex mirror

Correct Answer: (b) Both (A) and (C)
Solution:

Both (A) and (C). Concave mirrors and convex lenses act similarly. From a point source when the light ray hits a concave mirror or a convex lens, the beams of light that emerge are always parallel and the image is formed at infinity.

39. An object is placed in front of a convex mirror at a point between infinity and the pole of the mirror. The image formed is: [RRC Group D 25/08/2022 (Evening)]

Correct Answer: (c) virtual and erect
Solution:

Virtual and erect. Convex mirror (diverging mirror) diverges the rays of light, which fall on its reflecting surface. It is a curved mirror where the reflective surface bulges out toward the light source. The image formed in a convex mirror is always virtual and erect, whatever be the position of the object

40. A ray of light, passing through the centre of curvature, is incident on a concave mirror. It is reflected by an angle of ___________. [RRC Group D 26/08/2022 (Morning)]

Correct Answer: (b) 0°
Solution:

0°. It is because the angle of incidence is 0°. The ray passing through the centre of curvature is incident normally to the mirror. Angle of Incidence - The angle between the normal and the ray of light is called the angle of incidence. Angle of reflection - The angle between a reflected ray and the perpendicular to a reflecting surface drawn at the point of contact.