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

Total Questions: 50

31. The Outer space looks black because of: [RRC Group D 12/09/2022 (Evening)]

Correct Answer: (a) no scattering of light takes place
Solution:

No scattering of light takes place. Scattering depends upon particle or molecule size and the wavelength of the incident light. In space or on the Moon there is no atmosphere to scatter light. Since there is virtually nothing in space to scatter or re-radiate the light to our eyes, we see no part of the light and the sky appears to be black.

32. When a ray of light is incident obliquely at the pole of a concave mirror then the reflected ray will: [RRC Group D 12/09/2022 (Evening)]

Correct Answer: (a) return with Angle i = Angle r
Solution:

Return with Angle i = Angle r. The mirror is a reflective surface that reflects the incident light to form the image. The images can be either real or virtual. The convex mirror is a curved mirror in which the reflective surface will be pointing out towards the light source. If the ray of light is incident obliquely towards the pole of the convex mirror the ray will be reflected at an angle equal to the angle of incidence.

33. A concave mirror has a ________ towards the centre of the sphere with polish ________ the centre of curvature. [RRC Group D 13/09/2022 (Morning)]

Correct Answer: (d) depression, opposite to
Solution:

Depression, opposite to. Concave mirror and convex mirror can be formed from a single spherical glass by slicing it but polishing both the slices in the opposite manner. Concave mirror - Silver surface is away from the centre of curvature and reflecting surface is towards the centre of curvature. Convex mirror - Silver surface is towards the centre of curvature and reflecting surface is away from the centre of curvature.

34. The reddish appearance of the sun at the time of sunrise is due to: [RRC Group D 13/09/2022 (Morning)]

Correct Answer: (c) scattering of light
Solution:

Scattering of light. During sunrise and sunset, the rays travel a larger part of the atmosphere because they are close to the horizon. Therefore, light other than red is mostly scattered away. Most of the red light (longest wavelength), which is the least scattered, enters our eyes. This process occurs due to Rayleigh scattering. The phenomenon of scattering of light by dust, particles, smoke and water droplets suspended in air in colloidal form is known as “Tyndall effect” or “Tyndall Scattering”. It was first explained by John Tyndall in 1859.

35. The light from a point source is rendered parallel by a concave mirror. What is the position of the light source? [RRC Group D 13/09/2022 (Morning)]

Correct Answer: (c) At Focus
Solution:

At Focus. All the light rays which are parallel to the principal axis of a concave mirror, converge at the principal focus (F) after reflection from the mirror. Since a concave mirror converges to a parallel beam of light rays, it is also called a converging mirror.

36. A ray of light undergoes refraction through a triangular glass prism. The angle between the incident ray and emergent ray is called: [RRC Group D 13/09/2022 (Afternoon)]

Correct Answer: (a) angle of deviation
Solution:

Angle of deviation. The expression of the angle of deviation is ⇒ δ = (i + e) - A , Angle of refraction, The angle between the refracted ray and normal at the point of refraction. Angle of emergence: The angle of the light ray coming out of a medium perpendicular to the surface at the point of emergence

37. To obtain sharp signals from a dish antenna, the receiver of the dish antenna should be placed________. [RRC Group D 13/09/2022 (Evening)]

Correct Answer: (b) in front of the dish at F
Solution:

In front of the dish at F. In TV antenna dish concave mirror is used to concentrate the parallel beam of signals coming to the receiver situated at its focus.

38. When a ray of light travels from a denser to a rarer medium, it will: [RRC Group D 13/09/2022 (Evening)]

Correct Answer: (a) bend away from the normal
Solution:Bend away from the normal. Refractive Index (n) is the velocity of light in vacuum divided by the velocity of light in a medium, Refractive Index Formula n=c/v. Refractive Index Examples - Air (1.0003), Water (1.333), Diamond (2.42), Ice (1.31), Alcohol (1.36) and Fused quartz (1.46).

39. If the magnification of an image is -0.65, then the nature of the image is: [RRC Group D 14/09/2022 (Morning)]

Correct Answer: (b) real, inverted and smaller
Solution:

Real, inverted and smaller. Magnification = . 𝐼𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒 (𝑣)/ 𝑜𝑏𝑗𝑒𝑐𝑡 𝑠𝑖𝑧𝑒 (𝑢). The size or height of real and inverted images is considered negative and that of virtual and erect images is considered positive. According to question, magnification is - 0.65 which means the value of 𝑣/𝑢 is less than 1, which means  the size of the image is smaller than the size of the object. The negative sign implies that the image is real and inverted.

40. A beam of white light passes through a glass prism and a spectrum is obtained. Which of the following colour components bends the least? [RRC Group D 14/09/2022 (Morning)]

Yellow, Orange, Blue, Violet

Correct Answer: (c) Orange
Solution:

Orange. After passing through a prism, bending of light depends on the wavelength, light of shorter wavelength bends the most. Decreasing order of wavelength of light: Red > Orange >Yellow > Green > Blue > Indigo > Violet. Red light having maximum wavelength bends the least and violet light having least wavelength bends the most.