Practice portal › Ray Optics and Optical Instruments › Lenses

A lens is placed between a source of light and a wall. It forms images of area A₁ and A₂ on the wall, for its two different positions, the area of the source of light is

Asked in CBSE AIPMT 1995 · Lens formula and magnification

Answer: (1) √A₁A₂

Step-by-step solution

Given: one lens between a fixed source and a fixed wall, with two positions that each throw a sharp image, of areas A₁ and A₂.

Idea: in the displacement method the two positions exchange the object and image distances, so the two linear magnifications are reciprocals of one another.

m₁m₂=1

Areas go as the square of the linear magnification, so A₁=m₁²A and A₂=m₂²A for a source of area A.

A₁A₂=(m₁m₂)²A²=A²

A=√A₁A₂

Why the other options are wrong

More Lenses questionsAll Lenses questions →

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.

Practise this with a timer