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

Total Questions: 50

11. If the size of a spherical mirror increases in such a way that its radius of curvature gets doubled, then its focal length will _______. [RRC Group D 14/09/2022 (Morning)]

Correct Answer: (a) increase to double
Solution:

12. The path of a ray of light incident on an interface separating two transparent media is shown in the figure. The refractive index (n) of medium B with respect to medium A is given by: [RRC Group D 14/09/2022 (Afternoon)]

Correct Answer: (a) n > 1
Solution:

n > 1. Refractive index - Ratio of Speed of light in a vacuum to the speed of light in medium. n = 𝑠𝑖𝑛𝑖/𝑠𝑖𝑛𝑟, where i = angle of incidence, r = angle of reflection. When light rays travel from optically rarer medium (Speed of light is more) to denser medium (Speed of light is less) then n > 1. When light rays travel from optically denser medium to rarer medium then n < 1.

13. If m, v and u, respectively, represent magnification, image distance and object distance, then the correct relation between m, v and u for a lens will be: [RRC Group D 15/09/2022 (Morning)]

Correct Answer: (c) m = v/u
Solution:

14. A 12 cm long object is placed at a distance of 15 cm from a concave lens. Its virtual image of 8 cm is obtained at a distance of__________. [RRC Group D 15/09/2022 (Afternoon)]

Correct Answer: (b) -10 cm
Solution:

-10 cm. Given, height of the image (h’) = 8 cm, height of the object (h) = 12 cm, distance of the object (u) = -15 cm and distance of image (v) = ?.

15. An object of diameter 6 cm is placed at a distance of 10 cm in front of a lens with a power of +5.0 D. The diameter of the image of the object will be: [RRC Group D 17/09/2022 (Evening)]

Correct Answer: (d) 12 cm
Solution:

16. A child is looking at a reflecting surface of a Christmas tree ball which has a diameter of 10.0 cm, and the child observes an image of his face that is half the real size. How far is the child's face from the ball? [RRC Group D 18/09/2022 (Afternoon)]

Correct Answer: (d) –2.5cm
Solution:

17. Consider the dispersion of a medium as D for a wavelength λ. The dispersion of the same medium for wavelength 3λ will be: [RRC Group D 18/09/2022 (Afternoon)]

Correct Answer: (d) D/27
Solution:

18. When parallel beam of light rays are incident on the concave minor of radius of curvature 0.8 m, reflected rays: [RRC Group D 18/09/2022 (Evening)]

Correct Answer: (b) converge to a point at a distance 0.4 m from the concave surface
Solution:

f = R/2 = 0.8/2 = 0.4m
Where f = focal length, R = radius of
curvature

19. The refractive indices of mediums 1, 2 and 3 are 1.50, 1.36 and 1.54, respectively. If the speed of light in the mediums are v₁, v₂ and v₃ respectively, which of the following relations between them is correct? [RRC Group D 18/09/2022 (Evening)]

Correct Answer: (a) v₂ > v₁ > v₃
Solution:

20. Suppose Sita has kept a needle in front of a concave mirror of focal length f at a distance (f + x) and a real image of the needle is seen on a screen at a distance (f + y). Then the focal length f can be exposed as: [RRC Group D 19/09/2022 (Morning)]

Correct Answer: (b)
Solution: