Two thin lenses of powers +3.5 D and –1.5 D are placed in contact with each other. The power of the combinati…

Question

Two thin lenses of powers +3.5 D and –1.5 D are placed in contact with each other. The power of the combination is:
(A) –2.0 D
(B) +5.0 D
(C) +2.0 D
(D) –5.0 D

Accepted Answer

## Model Answer **(C) +2.0 D** When two lenses are placed in contact, the net power is the algebraic sum of their individual powers. $$P = P_1 + P_2 = +3.5	ext{ D} + (-1.5	ext{ D}) = +2.0	ext{ D}$$ Source: Chapter 9, Section 9.3.8 Power of a Lens --- ## Explanation The key formula is $P = P_1 + P_2 + \ldots$ (powers simply add algebraically). Remember that convex lens power is positive and concave lens power is negative. This is a straightforward one-step calculation — just add with signs carefully.

Science (086) — AI-generated practice question