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

Total Questions: 50

11. A student measured the magnification of a spherical lens and a spherical mirror. He found that both are +3.0. He would conclude that: [RRC Group D 19/09/2022 (Afternoon)]

Correct Answer: (d) the lens is convex but the mirror is concave
Solution:

The magnitude of magnification is greater than 1, it signifies that the image is enlarged. Since magnitude is 3, the image is 3 times bigger than the object. The mirror must be a concave mirror and the lens is convex.

12. The correct relation between v, u , and f for a spherical mirror is: [RRC Group D 19/09/2022 (Afternoon)]

Correct Answer: (d) 1/f = 1/u + 1/v
Solution:

1/f = 1/u + 1/v . SphericalΒ  mirror is a mirror which has the shape of a piece cut out of a spherical surface. Types - Concave and Convex mirror. Convex mirrors Use - Sunglasses, rear view mirrors, shaving mirror and concave mirrors Use - Reflectors, converging of light, solar cooker etc.

13. A light ray enters from medium A to medium B, and as a result, it bends away from the normal in the medium B. The refractive index of medium B relative to medium A is: [RRC Group D 20/09/2022 (Morning)]

Correct Answer: (c) less than unity
Solution:

Less than unity. Refraction - When light travels from one medium to another, it bends towards or away from the normal. When light moves from rarer to denser mediums, the rays bend towards the normal. In medium B, light rays bend away from the normal that indicates medium B is optically rarer than medium A. Now, refractive index

14. When light is incident along the normal and passes from air to water, then the direction of light will__________ [RRC Group D 20/09/2022 (Evening)]

Correct Answer: (a) not be changed
Solution:

Not be changed. Refraction of light - When the light rays either bend or change their direction while passing from one medium to another.

15. Suppose a point source is incident on a system and it produces a parallel beam of light with respect to the principal of the system. The system is: [RRC Group D 22/09/2022 (Morning)]

Correct Answer: (c) either a concave mirror or a convex lens
Solution:

Concave Mirror (converging mirror) - A mirror whose reflecting surface is toward the centre of the curvature. Convex Mirror (diverging mirror) - A mirror whose reflecting surface is away from the centre of the curvature. Concave lens - A lens that diverges the beam of light and is used to minimize the size of the object. Examples - Binoculars, Cameras, Lasers etc. Convex lens - A lens that converges the beam of light and is used to maximize the size of the object. Examples - Magnifying glasses, Microscopes etc.

16. Which of the following instruments use the principle of refraction? [RRC Group D 22/09/2022 (Morning)]

Correct Answer: (b) Spectacles
Solution:

Spectacles. Refraction is the bending of light, when light passes from one transparent medium to another, causing a change in speed, which results in a change in the direction of light. Example - Twinkling of stars in a clear sky, a Pool of water that appears to be less deep than it actually is, Rainbow formation in the sky, etc.

17. Suppose Raghu has kept an object in front of a concave mirror of focal length (f) at various distances (u) and he has measured the corresponding image distances (v). From the values of u and v, Raghu is able to plot a graph of magnification m against v. Which of the following options is true? [RRC Group D 22/09/2022 (Morning)]

Correct Answer: (d) It is a straight line with slope +1/f, and x intercept +f and y intercept -1
Solution:

Magnification v/s image distance - A straight line used to find magnification as a function of image distance. The formula of magnification (m) = -v/u .

18. When a ray is incident parallel to the principal axis of a convex lens then the refracted ray will pass through: [RRC Group D 22/09/2022 (Afternoon)]

Correct Answer: (d) principal focus
Solution:

Principal focus. Convex Lens- A lens that converges rays of light that convey parallel to its principal axis. Concave Lens - A lens that diverges a straight light beam from the source to a diminished, upright, virtual image. Ray Diagram- When a ray strikes concave or convex lenses obliquely at its optical center, it continues to follow its path. When a ray, passing through focus strikes concave or convex lenses, the reflected ray will pass parallel to the principal axis.

19. A point on the principal axis which is equidistant from the curved surface of a spherical mirror is: [RRC Group D 22/09/2022 (Afternoon)]

Correct Answer: (b) principal focus
Solution:

Principal focus. Centre of curvature is the center of the sphere of which the spherical mirror is a part. The center of the reflecting surface of a spherical mirror is a point called the Pole.
Mirror Formula β†’Β  1/𝑓 = 1/𝑒 + 1/𝑣.
Where, f = Focal length of the mirror,
v = Distance of image from the mirror,
u = Distance of the object from the mirror

20. A rainbow is formed by water droplets suspended in the atmosphere after the rain shower. The phenomenon responsible for occurring of rainbow consists of [RRC Group D 22/09/2022 (Afternoon)]

Correct Answer: (d) All combination of refraction, scattering and dispersion
Solution:

Rainbow is caused by the dispersion of sunlight by tiny water droplets, present in the atmosphere. Due to the dispersion of light and internal reflection, different colors are observed in the sky. The sequence of colors in the spectrum , VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).