Q160. In a concave mirror, a ray is incident parallel to the principal axis. After reflection, the ray passes through the _______.
[RRB Group D, 21 Aug 2026]
(A) Anywhere on the mirror
(B) Pole
(C) Focus
(D) Centre of curvature
Answer: (C) Focus
Explanation: A concave mirror is converging: rays parallel to its principal axis reflect through the principal focus. This occurs because the curved reflecting surface changes their directions according to the law of reflection. The focus lies in front of the mirror.
Q159. Which scenario best illustrates the use of a convex mirror based on the nature of its image?
[RRB Group D, 20 Aug 2026]
(A) A model uses it as a makeup mirror
(B) A scientist uses it to focus sunlight for heating
(C) A student uses it to obtain a real, inverted image on paper
(D) A shopkeeper uses it to monitor a wide area inside the store
Answer: (D) A shopkeeper uses it to monitor a wide area inside the store
Explanation: A convex mirror gives a wide field of view by forming virtual, upright and diminished images. Therefore, it is useful for surveillance inside shops and as a vehicle rear-view mirror. It cannot concentrate sunlight or produce screen images.
Q158. An object is placed between the optical centre and principal focus of a convex lens. What is the nature of its image?
[RRB Group D, 13 Aug 2026]
(A) Real, inverted and diminished
(B) Real, inverted and enlarged
(C) Virtual, inverted and diminished
(D) Virtual, erect and magnified
Answer: (D) Virtual, erect and magnified
Explanation: For an object inside the focal distance of a convex lens, emerging rays diverge and their backward extensions meet on the object’s side. This creates an upright, enlarged virtual image, which explains the working of a simple magnifying glass.
Q157. What is the angle between the incident and emergent rays called in the context of a prism?
[RRB Group D, 11 Aug 2026, Shift 2]
(A) The angle of incidence
(B) The angle of refraction
(C) The angle of emergence
(D) The angle of deviation
Answer: (D) The angle of deviation
Explanation: Light refracts at both faces of a prism, changing its overall direction. The angular difference between the original direction of the incident ray and the final emergent ray is the angle of deviation, not either individual refraction angle.
Q156. The refractive index of water relative to air is the ratio of which speeds?
[RRB Group D, 11 Aug 2026, Shift 3]
(A) Sum of speeds in air and water
(B) Difference of speeds in air and water
(C) Speed in water divided by speed in air
(D) Speed in air divided by speed in water
Answer: (D) Speed in air divided by speed in water
Explanation: Relative refractive index n(water/air) equals v(air)/v(water). Light slows as it enters water from air, so the relative index is greater than one. The ratio is dimensionless because both speeds have identical units.
Q155. Which image is formed by a concave mirror when the object lies between its focal point and centre of curvature?
[RRB Group D, 10 Aug 2026]
(A) Real, inverted and magnified
(B) Virtual, upright and diminished
(C) Real, upright and same size
(D) Virtual, inverted and magnified
Answer: (A) Real, inverted and magnified
Explanation: An object between F and C produces reflected rays meeting beyond C. Because the rays physically intersect, the image is real; its orientation is inverted and its height exceeds the object’s. This is the magnifying real-image configuration of concave mirrors.
Q154. Which application uses refraction to focus light onto a specific point for clear vision?
[RRB Group D, 9 Aug 2026]
(A) The human eye lens adjusting its shape
(B) A glass prism splitting sunlight
(C) A plane mirror reflecting images
(D) A shadow formed behind an object
Answer: (A) The human eye lens adjusting its shape
Explanation: The eye lens refracts entering light and focuses it on the retina. Ciliary muscles vary the lens curvature and therefore its optical power, enabling clear sight at changing distances. This change in focusing ability is called accommodation.
Q153. The refracted ray inside a triangular prism bends ________.
[RRB Group D, 9 Aug 2026]
(A) Perpendicular to the base
(B) Toward the base of the prism
(C) Along the base
(D) Away from the base
Answer: (B) Toward the base of the prism
Explanation: Refraction at a prism’s surfaces results in a net deviation toward its base. The ray bends toward the normal on entering glass and away from the normal on leaving it. Their geometry produces overall deviation from the original course.
Q152. What is the angle between the two refracting faces of a triangular glass prism called?
[RRB Group D, 6 Aug 2026]
(A) Angle of refraction
(B) Angle of deviation
(C) Angle of the prism
(D) Angle of incidence
Answer: (C) Angle of the prism
Explanation: The angle formed where the two refracting faces meet is the prism angle, usually represented by A. It is a fixed geometric property of the prism, whereas angles of incidence, emergence and deviation depend on the light’s path.
Q151. Why does a pencil partially immersed in water appear bent at the surface?
[RRB Group D, 6 Aug 2026]
(A) Reflection from the pencil
(B) The pencil emits light at another angle
(C) Light changes direction between water and air
(D) Water physically changes the pencil’s thickness
Answer: (C) Light changes direction between water and air
Explanation: Rays coming from the submerged pencil refract when travelling from water into air, bending away from the normal. The eye traces them backward in straight lines and sees the submerged part at a shifted apparent position, making the pencil appear bent.