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

Total Questions: 50

1. In the absence of atmosphere, the color of the sky would be: [RRC Group D 01/09/2022 (Afternoon)]

Correct Answer: (c) black
Solution:

black. Sky appears blue due to scattering. In absence of atmosphere no scattering will occur. Therefore the sky will be seen black. Our eyes are more sensitive to the blue light thus we see the sky as blue. phenomenon of scattering of light - Tyndall effect.

2. In which of the following cases does a concave mirror form a real image? [RRC Group D 01/09/2022 (Afternoon)]

(i) Object placed between focus and pole
(ii) Object placed at infinity
(iii) Object placed at focus

Correct Answer: (a) Both (ii) and (iii)
Solution:

Both (ii) and (iii). Concave mirrors can produce both real and virtual images. When the concave mirror is placed very close to the object, a virtual and magnified image is obtained and if we increase the distance between the object and the mirror, the size of the image reduces and real images are formed. So, the images formed are real (except when the object is between pole and focus).

3. An optical device X forms an image CD for an object AB as shown in the figure. The device X is a: [RRC Group D 01/09/2022 (Evening)]

Correct Answer: (a) concave mirror
Solution:

A concave mirror forms an erect, virtual and enlarged image as shown in the question figure when the object is between focus and the pole of the mirror. A concave mirror has a reflective surface that is curved inward and away from the light source. Concave mirrors reflect light inward to one focal point. Unlike convex mirrors, the image formed by a concave mirror shows different image types depending on the distance between the object and the mirror.

4. Rays coming from the sun are refracted by the atmosphere. Due to this, the apparent sunset is about ______ the actual sunset. [RRC Group D 01/09/2022 (Evening)]

Correct Answer: (d) 2 minutes after
Solution:

2 minutes after. We are able to see the sun 2 minutes before the actual sunrise and 2 minutes after the actual sunset due to refraction of light by the atmosphere. The refraction of light caused due to different layers of the atmosphere at different temperatures (different refractive indices) is called the atmospheric refraction. Some Examples:- Twinkling of stars, Apparent higher position of a star, Early sunrise and delayed sunset, Flattened appearance of sun during sunrise and sunset.

5. A ray of light is incident on a refracting surface AB of a glass prism, kept in air, and emerges out of the other refracting surface AC. Consider the following statements : [RRC Group D 02/09/2022 (Morning)]

(a) The angle of refraction at surface AB is less than the angle of incidence. (b) The angle of refraction at the surface AC is more than the angle of incidence, Which of the above statements is/are correct?

Correct Answer: (b) Both (a) and (b)
Solution:

Both (a) and (b). When a light ray falls on one side of the prism, it gets refracted (bent towards the normal). It is because it has moved from an optically rarer medium (air) towards optically denser medium (prism). When this ray reaches the other side of the prism, it gets refracted again (bent away from normal). It is because now it has moved from an optically denser medium (prism) towards optically rarer medium (air).

6. Which of the following point(s) always lie(s) on the principal axis of a lens? [RRC Group D 02/09/2022 (Morning)]

(i) Point of refraction (ii) Optical Centre (iii) Point of incidence

Correct Answer: (c) Only (ii)
Solution:

Only (ii). The point on the principle axis inside the lens, through which a light ray passes without any deviation is called the optical center (O) of the lens. A lens is a transmissive optical device that focuses a light beam by following the phenomenon called refraction. A lens consists of an imaginary line called the principal axis on which the optical center is present. The point of incidence is the point at which light strikes the surface of the lens.

7. Solve the following question? [RRC Group D 02/09/2022 (Morning)]

Correct Answer: (c)
Solution:

8. Which of the following diagrams correctly represents the path of a light ray incident parallel to the principal axis after refraction through the lens? [RRC Group D 02/09/2022 (Evening)]

Correct Answer: (b)
Solution:

In the figure, Object location is at Infinity, so image is formed at Focus (F), image nature is Real and Inverted and Image size is Diminished.

9. A ray of light is incident on a concave mirror at point M. The ray makes an angle of 10° with a line joining M to the center of curvature. The ray is reflected at an angle of _______. [RRC Group D 02/09/2022 (Evening)]

Correct Answer: (a) 10°
Solution:

10°. When a ray of light incident on a concave mirror from its centre of curvature it retraces the path of the incident ray i.e., it goes along the same path. So if a ray of light is incident on a concave mirror at point M and the ray makes an angle of 10° with a line joining M to the centre of curvature. Then the ray is reflected at an angle of 10°.

10. Due to atmospheric refraction, the apparent position of a star is slightly ________ than its actual position, when viewed from near the horizon, and this apparent position_________ This results in twinkling of stars. [RRC Group D 05/09/2022 (Morning)]

Correct Answer: (b) higher, keeps on changing
Solution:

Higher, Keeps on changing. Actual position of the star is different from apparent position because - star acts as a point source of light, starlight undergo refraction while entering the atmosphere. Twinkling of a star is due to atmospheric refraction of starlight.