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

Total Questions: 50

31. Light travels from air into water with an index of refraction of 1.33. The light ray will : [RRC Group D 28/09/2022 (Afternoon)]

Correct Answer: (c) Bend towards the normal
Solution:

Bend towards the normal. Refractive index is the ratio of the velocity of light in a vacuum to its velocity in a specified medium. When the ray of light travels from an optically rarer medium to an optically denser medium its speed slows down and the refracted ray gets bends towards the normal but if it moves from an optically denser medium to an optically rarer medium it bends away from the normal.

32. A concave mirror of focal length f produces a real image at a distance v from the pole, when an object is kept at the distance u from the pole. Here, focal length of the given mirror is : [RRC Group D 28/09/2022 (Afternoon)]

Correct Answer: (c) (u v) / (u + v)
Solution:

(u v) / (u + v). Concave Mirror (Converging mirror) - If a hollow sphere is cut into parts and the outer surface of the cut part is painted, then it becomes a mirror with its inner surface as the reflecting surface. The image formed by the concave mirror can be small or large and can be real or virtual. Example - Headlights, Shaving mirrors, Solar furnaces, Searchlights, Torches, Flashlights, Dental Mirror etc.
Mirror formula (1/f = 1/v + 1/u).

33. When white light is incident on a prism, its dispersion takes place. In this context, select the correct option. [RRC Group D 28/09/2022 (Afternoon)]

(A) Red light gets bent the most in a prism.
(B) Violet color of light has the least speed in the prism.
(C) The refractive index of violet colored light is highest.
(D) When the prism is held upright, the violet color is at the top and the red color is at the bottom.
(E) The formation of a rainbow is also due to dispersion.

Correct Answer: (c) (B), (C) and (E)
Solution:

(B), (C) and (E). When white light passes through a glass prism, it splits into its spectrum of colours (in order violet, indigo, blue, green, yellow, orange, and red) and this process of splitting white light into its constituent colours is known as dispersion.

34. Which of the following statements with regard to the principal axis of a spherical mirror is/are correct? [RRC Group D 28/09/2022 (Afternoon)]

(a) The pole on the principal axis is similar to the origin of a Cartesian coordinate axis plane.
(b) Distances measured from the pole, along the principal axis opposite to the direction of the incident light are negative.
(c) Heights of the objects or image above the principal axis and perpendicular to it are considered negative.

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

Only (a) and (b). Terms associated with the spherical mirrorsPole(P) - The geometrical center of the spherical mirror is called its pole. Centre of curvature(C) - The center of the imaginary sphere of which the mirror is a part is called the center of the curvature. Principal focus(F) - A point on that spherical mirror's principal axis where parallel light rays intersect (meet) or emerge to deviate after reflection. Focal Length - The distance between the pole and the focus is called the focal length. The focal length is half the radius of curvature. Aperture - The portion of a mirror from which the reflection of light actually takes place is called the aperture of the mirror.

35. Identify the correct statement(s) with respect to the reflection of light by a spherical mirror from among the following. [RRC Group D 28/09/2022 (Evening)]

(A) A convex mirror can only form real and inverted images.
(B) A concave mirror can form real, inverted and virtual, erect images.
(C) Images formed by convex mirrors are either diminished, same size or enlarged depending on the position of the object.
(D) Images formed by concave mirrors are either diminished, same size or enlarged depending on the position of the object.

Correct Answer: (a) (B) and (D) are only correct
Solution:

(B) and (D) are only correct. Image formation by Concave mirror - If an object is close to the mirror a magnified, erect and virtual image is obtained. If we increase the distance between object and mirror, the size of the image reduces and a real and inverted image is formed. Image formation by Convex mirror : Always form virtual, erect and diminished images.

36. The refractive index of a material can be linked with relative ____________ of propagation of light in different media. [RRC Group D 28/09/2022 (Evening)]

Correct Answer: (d) speed
Solution:

Speed. Refractive index - The measure of bending of a light ray when passing from one medium to another. It can also be defined as the ratio of the velocity of a light ray in an empty space to the velocity of light in a substance. n = c/v. Where c is the velocity of light in a vacuum ( 3 Γ— 10⁸ m/s). Refractive indexΒ  of different mediums - Air (1.0003), Water (1.333). The vacuum has a refractive index of 1.

37. When a thin beam of white light is passed through a prism, the light _____. [RRC Group D 29/09/2022 (Morning)]

Correct Answer: (d) will be anagrammed
Solution:

Will be anagrammed. Dispersion of light - When white light is passed through a glass prism it splits from the sun into 7 colours - Violet, Indigo, Blue, Green, Yellow, Orange and Red (VIBGYOR).

38. Which of the following statements is/are true regarding the centre of curvature of a spherical mirror? [RRC Group D 29/09/2022 (Morning)]

(S-I) Rays of light passing in any direction through the centre of curvature are normal to the mirror.
(S-II) A ray of light passing through the centre of curvature, and the principal focus is also normal to the mirror.
(S-III) The angle of incidence of the ray of light passing through the centre of curvature onto the mirror is 90Β°.

Correct Answer: (c) (S-I) only
Solution:

(S-I) only. Center of Curvature (C) - It is the centre of the hollow sphere which the mirror forms a part. In the case of the Concave mirror, it lies in front of the mirror, while in the case of the Convex mirror it lies behind the mirror. The distance between the Pole and the Principal Focus of the spherical mirror is termed as the focal length.
Focal Length = π‘…π‘Žπ‘‘π‘–π‘’π‘  π‘œπ‘“ π‘π‘’π‘Ÿπ‘£π‘Žπ‘‘π‘’π‘Ÿ/2 .

39. The correct relation between the focal length of a lens and its power is: [RRC Group D 29/09/2022 (Afternoon)]

Correct Answer: (a) P = 1/𝑓
Solution:

P = 1/𝑓. Power of a lens (P) is the reciprocal of its focal length. SI unit - dioptre (D). One dioptre is the power of a lens whose focal length is 1 meter (1D = 1π‘šβ»ΒΉ ). The power of a convex lens - positive, concave lens - negative.

40. In the following table, mirror, its application and the justification for the application are given. Identify the rows in which the information is completely correct, with regard to given spherical mirrors in column 2. [RRC Group D 29/09/2022 (Afternoon)]

Correct Answer: (d) Only 1, 2 and 3
Solution:

Only 1, 2 and 3. Uses of Convex mirror: sunglasses, rear-view mirror in Automobiles, utilized in ATMs and other places for security reasons, reflector for street lights. Uses of concave mirror: Shaving mirrors, Head mirrors, Ophthalmoscope, Astronomical telescopes, Headlights, Solar furnaces. The image formed by a convex mirror is located behind the mirror, always a virtual and erect image and reduced in size.