1995 General Studies, all questions
UPSC Prelims 1995 · General Studies
Question 115: Science and Technology
An air bubble in water will act like a
aconvex mirror
bconvex lens
cconcave mirror
dconcave lens
AnswerThe answer is (d).
An air bubble in water is a pocket of a medium with lower refractive index than the water around it. Light passing through the bubble is bent away from the axis, the opposite of what a convex lens made of a denser material does, so the bubble acts as a diverging, or concave, lens even though its shape is round. Remember: a lens that is optically rarer than its surroundings reverses its behaviour.
Why each option is right or wrong
- (a) A mirror works by reflection, not by refraction through the bubble.
- (b) A convex lens converges light only if it is denser than its surroundings.
- (c) A concave mirror works by reflection too.
- (d) Right: a concave, diverging lens.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1995, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.