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

Total Questions: 50

11. The angle of incidence for a ray of light incident on a glass slab along its normal, is: [RRC Group D 05/09/2022 (Afternoon)]

Correct Answer: (a) 0°
Solution:

0° . Angle of incidence - is equal to the reflected angle through the law of reflection. When a light ray hits a surface normally, the angle between the incident ray and the normal is zero. when the wave is parallel to the surface it's incident angle of incident will be 90° .

12. For a ray of light undergoing refraction through a triangular glass prism, which of the following statements is/are always correct? [RRC Group D 05/09/2022 (Evening)]

(A) Angle of incidence is the angle between the incident ray and normal at the point of incidence.
(B) Angle of incidence is equal to angle of emergence.
(C) Angle of deviation is the angle between incident ray and emergent ray.

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

Both (A) and (C). Refraction is the bending of light when it goes from one medium to another. When a ray of light passes through a glass prism, refraction of light occurs both when it enters the prism as well as when it leaves the prism. Since the refracting surfaces are not parallel, therefore, the emergent ray and incident ray are not parallel to one another and the ray of light is deviated on passing through the prism.

13. The refractive index of mediums 1, 2 and 3 are 1.31, 1.36 and 1.44 respectively. If the speed of light in the medium is 𝑉₁, 𝑉₂ and 𝑉₃, then which of the following relation is correct between them? [RRC Group D 06/09/2022 (Morning)]

Correct Answer: (d) 𝑉₁ > 𝑉₂ > 𝑉₃
Solution:

𝑉₁ > 𝑉₂ > 𝑉₃. The refractive  index of a medium is inversely proportional to the speed of light in that medium i.e. n ∝ 1/v. The more the refractive index of a medium, the less is the speed.

14. A ray of light is incident on one refracting surface AB of a glass prism and emerges out on the other refracting surface AC. Consider the following statements: [RRC Group D 06/09/2022 (Morning)]

(A) The angle of refraction at surface AB is the same for different colors of white light.
(B) The angle of refraction at surface AC is different for different colors. Which of the above statements are correct?

Correct Answer: (b) only (B)
Solution:

Only (B). When light enters into a prism, it gets refracted because it enters from one medium (air) to another (glass). When white light is passed through a prism, it splits into seven colors of VIBGYOR (violet, indigo, blue, green, yellow, orange, red).

15. A beam of white light passes through a glass prism and a spectrum is obtained. Which of the following colour components bends the most? [RRC Group D 06/09/2022 (Afternoon)]

Green, Red, Indigo, Blue

Correct Answer: (c) Indigo
Solution:

Indigo. This is because Indigo has the lowest velocity in glass and least wavelength among the given options. So, it bends the most.

16. An object is placed in front of a concave mirror at a point lying between its focus F and the center of curvature C. The image will be formed at a point located at _______, and will be __________. [RRC Group D 06/09/2022 (Afternoon)]

Correct Answer: (c) beyond C, Large
Solution:

Beyond C, Large. Image Formation by Concave Mirror - Object placed at Infinity - Image is real and inverted and formed at the focus, At the centre of curvature - real image is formed at the centre of curvature, Between the centre of curvature and principal focus - real image is formed beyond the centre of curvature, At the principal focus - real image is formed at infinity, between focus and pole - virtual and erect image is formed behind the mirror.

17. Milk appears white when surrounded by white light because the particles in the milk are ______ compared to the wavelengths of different colors of white light that fall on it, and all colors of white light are scattered by ____. [RRC Group D 06/09/2022 (Evening)]

Correct Answer: (a) large, almost equal
Solution:

Large, almost equal. When light hits these casein micelles it causes the light to refract and scatter resulting in milk appearing white. Caseins are one of the main types of protein in milk which cluster together with calcium and phosphate to form tiny particles called micelles.

18. A ray of light in glass is incident at an angle of 30° on the surface separating glass from air. The ray is refracted in the air at an angle of_____ and the refracted ray______in the plane of the incident ray. [RRC Group D 08/09/2022 (Afternoon)]

Correct Answer: (b) more than 30°, lies
Solution:

More than 30°, lies. Refraction of light - Refraction is the change in the direction of a wave passing from one medium to another. Examples - Twinkling of stars in a clear sky, Pool of water appears to be less deep than it actually is, Rainbow formation in the sky.

19. An object is placed in front of a concave mirror at a point beyond its centre of curvature C. The image is formed at a point_______ and_______ is: [RRC Group D 08/09/2022 (Evening)]

Correct Answer: (a) between F and C, diminished
Solution:

between F and C, diminished. Concave mirrors can produce real as well as virtual images. Position of object and formation of images is as follows: when object is at infinity - diminished, real, point size, and inverted image will form at focus (F). If the Object is placed exactly at C - a real and inverted Image of the same size will form at C. If the Object is at F - real, inverted and magnified image will form at infinity. object is placed between F and the pole (P) of the mirror - Virtual, erect and magnified image will form appearing behind the mirror.

20. An object is placed on the principal axis of a concave lens, at a point between infinity and its optical centre O. Its image formed is_______. [RRC Group D 08/09/2022 (Evening)]

Correct Answer: (b) virtual and diminished
Solution:

Virtual and diminished. Concave lens - diverges a straight light beam from the source to a diminished, upright, virtual image, irrespective of the position of the object; Uses - Telescopes and binoculars to magnify objects, In short-sightedness (myopia). Focal length of a concave lens is negative.