Railway Science (Physics-Light and Optics) (Part-VII)

Total Questions: 50

1. An object is placed at a distance of 40 cm from a convex lens having focal length 20 cm. Which option given below, correctly describes the nature and the relative size of the image formed in the respective order? [RRC Group D 02/09/2022 (Evening)]

Correct Answer: (d) Real, inverted and same sized
Solution:

Real, inverted and same sized.
Given,
Object distance (u) = - 40 cm,
Focal length (f) = 20 cm
So, Using lens formula  1/f = 1/𝑣 - 1/𝑢
⇒ 1/v = 1/40 = v = 40cm. In Convex Lens when v is positive then the image formed is real and inverted while the v is negative then the image formed is virtual and erect. Also, the image formed at center of curvature(C) because C = 2f ⇒ C = 40cm. So, Image is same size as object. Hence, Image formed is Real, inverted and same sized.

2. An object is placed in front of a concave mirror of focal length 6 cm, at a distance of 24 cm. The magnification produced by the mirror is_______. [RRC Group D 05/09/2022 (Morning)]

Correct Answer: (a) - 1/3
Solution:

3. If P, F and C represent the pole, principal focus and centre of curvature, respectively, of a concave mirror, then PC is equal to: [RRC Group D 05/09/2022 (Afternoon)]

Correct Answer: (c) 2PF
Solution:In this figure.
MPN = Concave spherical mirror
P = Pole
F = Principle focus
C = Centre of curvature
PF = Focal length of mirror
PC = Radius of curvature of mirror
The rays that are near the principal axis
(paraxial rays) and parallel to it converge to a single point on the axis after emerging from the spherical mirror. And this is half of the radius of the curvature in a spherical mirror. So the PC is equal to 2PF.

4. An object of size 4.0 cm is placed at a distance of 24 cm in front of a convex mirror of focal length 8 cm. The image formed will be _______, and its height will be ______. [RRC Group D 06/09/2022 (Morning)]

Correct Answer: (a) erect, 1.0 cm
Solution:

5. The focus of a convex mirror is at a distance of 30 cm from its pole. Its centre of curvature will be at a distance of __________from the focus. [RRC Group D 08/09/2022 (Morning)]

Correct Answer: (a) 30 cm
Solution:

30 cm. For a convex mirror, the radius of curvature (R), is twice its focal length (f). Here, f = 30cm, R = 2f = 2 × 30 = 60 cm. Relation Between Focal Length and Radius of Curvature PC = PF + FC. PF = focal length f , PC = radius of curvature R, FC = Distance between focus and R . Given PF = 30cm, PC = 60 cm. Then FC = PC − PF = 60 − 30 = 30 cm. Its centre of curvature will be at a distance of 30 cm from the focus.

6. A ray of light in air is incident at an angle of 30° on the surface of water in a jar. The ray is refracted in the water at an angle of ______and_______ in the plane of the incident ray. [RRC Group D 08/09/2022 (Morning)]

Correct Answer: (d) less than 30°, lies
Solution:

7. A diverging mirror of focal length 20 cm forms an image one-third the size of the object. At what distance from the mirror is the object located? [RRC Group D 08/09/2022 (Afternoon)]

Correct Answer: (a) -40 cm
Solution:

8. A ray of light in air is incident at an angle of 60° on the surface separating air from a medium of refractive index √3. The ray is refracted in the medium at an angle of______. [RRC Group D 09/09/2022 (Morning)]

Correct Answer: (c) 30°
Solution:

9. If the power of a convex lens is 3 dioptre, then its focal length will be: [RRC Group D 09/09/2022 (Afternoon)]

Correct Answer: (a) +0.33 m
Solution:

+0.33 m.
Power of convex lens (P) = 3 D (Dioptre)
Focal length (f) = 1/p ⇒ f = 1/3 = 0.33 m

10. The refractive indices of two transparent media A and B are 3/2 and 4/3, respectively. The refractive index of medium A with respect to medium B is equal to [RRC Group D 13/09/2022 (Morning)]

Correct Answer: (c) 9/8
Solution: