Railway Science (Physics-Light and Optics)

Total Questions: 50

1. Which of the following types of images can be obtained on a screen? [RRC Group D 17/08/2022 (Morning)]

(a) Real and enlarged
(b) Real and diminished
(c) Virtual and enlarged
(d) Virtual and diminished

Correct Answer: (c) Both (a) and (b)
Solution:Both (a) and (b). Real and enlarged image is obtained when Object placed between the centre of curvature (c) and focus (F) (Concave Mirror) and when Object placed between the focus (F₁) and centre of curvature (2F₁) (Convex Lens). Real and diminished - When an object is placed beyond the center of curvature (C) in a concave mirror and beyond (2F₁) in a convex lens. Virtual and enlarged - convex lens. Virtual and diminished - A convex mirror always forms a virtual, erect, and diminished image, irrespective of the position of the object.

2. If a ray of light is incident passing through the centre of curvature of a concave mirror, then the angle between the incident ray and the reflected ray will be equal to: [RRC Group D 17/08/2022 (Morning)]

Correct Answer: (a) 0°
Solution:0°. As the ray of light passes through the Center of Curvature of a Concave mirror, it strikes the mirror along the normal (i.e. it incidences onto the mirror at 90 degrees and 0 degrees with normal). Hence the Incident ray coincides with the normal. Therefore the Angle of Incidence is 0 degrees.

3. In the figure shown below, the incident ray and the emergent ray in the respective order are given by: [RRC Group D 17/08/2022 (Afternoon)]

Correct Answer: (b) AB and CD
Solution:AB and CD. Incident Ray = AB and Emergent Ray = CD. Refracted ray = BC. An Incident ray is a rectilinear ray of light that strikes a surface. Emergent Ray is a ray emerging after reflection or refraction or dispersion.

4. The distance between the pole and the center of curvature of a spherical mirror, in terms of its focal length, is equal to ________. [RRC Group D 17/08/2022 (Afternoon)]

Correct Answer: (d) 2f
Solution:2F. F = R/2, so R = 2F. The Radius of Curvature (R) (of a Spherical mirror) - radius of the circle of which the Spherical mirror is a part. The Center of Curvature (of a Spherical mirror) - It is defined as the Center of the Sphere of which the Spherical Mirror is a part. The Focal Length (F) (of a Spherical mirror) - It is the distance between the pole and the principal focus of the mirror.

5. A student focusses a sharp image of sun using a spherical mirror on a sheet of paper, which starts to burn after some time. Which of the following statements / statements about the mirror is/are correct? [RRC Group D 17/08/2022 (Evening)]

(A) It is concave spherical mirror
(B) It has positive focal length
(C) It is a converging mirror

Correct Answer: (a) Both (A) and (C)
Solution:Both (A) and (C). A Concave mirror is a Converging mirror on which when parallel rays fall then all the rays get converged at a point which is known as the focus of the Concave mirror and as all the rays coincide at one point and therefore the intensity at that point will increase and that is why when a paper is kept at the focal point of the Concave mirror exposed to sunlight for some time the paper catches fire. The concave mirror forms a virtual and magnified image. The focal length of a Concave mirror is negative because the Focus of a Concave mirror is in front of the mirror.

6. A ray of light is incident on an interface separating two media along the normal to the interface. The angle between the incident ray and refracted ray is equal to: [RRC Group D 17/08/2022 (Evening)]

Correct Answer: (b) 0°
Solution:0°. Incident angle - The angle between the incident ray and the normal to the surface. Incident ray - The ray of light that hits the surface. Reflected ray - The ray that gets reflected away. Reflection - phenomenon of returning light from the surface of an object when the light is incident on it. Refraction - change in the direction of a wave passing from one medium to another.

7. Which of the following statements are correct? [RRC Group D 18/08/2022 (Morning)]

(A) For a lens the first principal focus is the position of the object whose image is at infinity
(B) For a lens the first principal focus is the position of the object whose image is formed at twice the focal length.
(C) For a lens the second principal focus is the position of the real image whose object is at infinity
(D) For a lens the second principal focus is the position of the object whose image is formed at twice the focal length

Correct Answer: (c) Both (A) and (C)
Solution:Both (a) and (c) . Image formation by Convex Lens - Object Position (Image position, Image feature) - At Infinity (at focus F₂ , highly diminished, real and inverted), At 2F₁ (At 2F₂ , same size, real and inverted), between F₁ and 2F₁ (beyond 2F₂ , enlarged, real and inverted), at focus F₁ (At infinity, highly enlarged, real and inverted), between focus F₁ and optical centre O (on the same side of lens as the object, enlarged, virtual and erect), beyond 2F₁ (Between F₂ and 2F₂ , diminished, real and inverted).

8. A boy focusses a sharp image of a distant object on a screen using a lens. The distance between the lens and screen is approximately equal to: [RRC Group D 18/08/2022 (Morning)]

Correct Answer: (d) f
Solution:f (Focal Length). A convex lens converges all the rays coming from a distant object on its focus to form a real image. If the image is obtained on a screen placed at the focal point of the lens, then the distance between the lens and the screen would be the focal length (f) of the lens.

9. An object is placed at the principal focus of a concave lens. Which of the following options represents the characteristics of the image formed? [RRC Group D 18/08/2022 (Morning)]

Correct Answer: (b) Virtual and highly diminished
Solution:Virtual and highly diminished. Formation of image by concave lens : Object Position (Image position, Image feature) - At infinity (At focus, virtual and highly diminished), Between lens and infinity ( At lens and focus on the same side, Virtual and diminished).

10. An optical device Y has positive focal length. Y is: [RRC Group D 18/08/2022 (Afternoon)]

Correct Answer: (c) either a convex lens or a convex mirror
Solution:The Focal length of the convex lens is positive because a light ray parallel to the principal axis passes through a focus on the other side of the lens. Uses: to correct Hypermetropia, as a magnifying glass. The focal length of a convex mirror is at the right-hand side of the optical centers. So, it is taken as positive. Uses: Used in sunglasses, as a rear-view mirror in automobiles and as a reflector for street lights.