Home › ICSE Class 10 › physics › Refraction through a Lens › Two thin lenses of focal lengths +20 cm and +25 …
Two thin lenses of focal lengths +20 cm and +25 cm are placed in contact. Power of combination:
A+9 D
B+5 D
C+10 D
D+1 D
Answer & Solution
Correct answer: A. +9 D
1. Each power: P = 1 / f.
2. P1 = 1 / 0.20 = 5 D and P2 = 1 / 0.25 = 4 D.
3. Combination power = P1 + P2.
4. P = 5 + 4 = +9 D.
5. So the combination is +9 dioptres.
_Source: Selina Concise Physics ICSE Class 10, Ch 5 'Refraction through a Lens' (aplustopper.com extract)_
Related questions
Linear magnification produced by a converging lens for an object at 2F is:Cross-section of a convex lens looks like:Two lenses of powers +3 D and -5 D are placed in contact. The combination:A virtual image:Image formed by a convex lens with object at infinity is:If both surfaces of a thin lens have equal radii of curvature R, the lens is called:An object is placed beyond 2F from a convex lens. Image position is:Which is the principal use of a concave lens?