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

Total Questions: 50

31. A stalactite of size 10.0 m is found in Brazil. If this stalactite is placed at a distance of 20.0 m from a concave mirror and a real image of size 30.0 m is formed, then the principal focus of the mirror is at: [RRC Group D 26/09/2022 (Morning)]

Correct Answer: (a) - 30.0 m
Solution:

32. A needle of height 6 cm is placed at a distance of 20 cm in front of a lens with a power of -2.5 D. The height of the image of the needle will be: [RRC Group D 26/09/2022 (Morning)]

Correct Answer: (a) 4 cm
Solution:

33. If light enters from air to some medium A having a refractive index of 1.33, then what is the speed of light in the medium A? [RRC Group D 26/09/2022 (Evening)]

Correct Answer: (c)
Solution:

34. A light ray is travelling from air medium to water medium (refractive index = 1.3) such that angle of incidence is x degree and angle of refraction is y degree. The value of ratio (sin y)/(sin x) is: [RRC Group D 26/09/2022 (Evening)]

Correct Answer: (b) 1/1.3
Solution:

35. A coin of diameter 10 cm is placed at a distance 3.5f from the pole of a concave mirror of focal length f. The linear magnification and the diameter of the image are: [RRC Group D 27/09/2022 (Morning)]

Correct Answer: (a) 2/5 and 4cm respectively
Solution:

36. Refractive index of flint glass is 1.56. Then the critical angle(πΌπ–ˆ) for glass air interface can also be expressed as Sin πΌπ–ˆ equals: [RRC Group D 27/09/2022 (Afternoon)]

Correct Answer: (a) 0.64
Solution:

Critical angle = 1/π‘Ÿπ‘’π‘“π‘Ÿπ‘Žπ‘π‘‘π‘–π‘£π‘’ 𝑖𝑛𝑑𝑒x

= 1/1.56 = 0.64
The ratio between the speed of light in vacuum to speed of light in a medium is the refractive index (ΞΌ or n).

37. An ice-ball of 6 cm diameter is placed 30 cm in front of a concave mirror and its principal focus is double the distance of the object. Following the new Cartesian sign convention, the diameter of the image is: [RRC Group D 27/09/2022 (Afternoon)]

Correct Answer: (b) 12 cm
Solution:

38. Suppose Ram has placed a ball 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. Ram is able to plot a graph of 1/v against I/u. From the graph, Ram has observed that x intercept and y intercept are 0.1 cm and 0.11 cm, respectively. Then the focal length of the mirror is: [RRC Group D 27/09/2022 (Evening)]

Correct Answer: (c) 9.09 cm
Solution:

39. In the Leviathan telescope in Ireland, a concave mirror of focal length 3.0 m is used. If an image of height 80 cm is formed at a distance of 4.0 m, then the object height, object distance and magnification are (the object is placed in front of the mirror): [RRC Group D 27/09/2022 (Evening)]

Correct Answer: (a) 2.4 m, 12 m and 1/3 respectively
Solution:

40. A concave mirror forms a real image of three times the size of an object on a screen. The object and screen are then moved until the image is six times the size of the object. If the shift of the screen is 39 cm, then the focal length of the mirror is: [RRC Group D 28/09/2022 (Morning)]

Correct Answer: (c) 13 cm
Solution: