A thin convex lens made from crown glass (μ = 3/2) has focal length f. When measured in two different liquids of refractive indices 4/3 and 5/3, it has focal lengths f₁ and f₂ respectively. The correct relation between the focal lengths is:
Options

Question

A thin convex lens made from crown glass (μ = 3/2) has focal length f. When measured in two different liquids of refractive indices 4/3 and 5/3, it has focal lengths f₁ and f₂ respectively. The correct relation between the focal lengths is:

Options

G1 Physics · Accepted Answer

Derived solution: Step 1: Use the thin-lens formula 1/f = 1/v - 1/u with m = v/u. For lens material/medium changes use the lens-maker relation with the relative refractive index; powers of thin lenses in contact add. Step 2: Substitute the values given in the question and apply the geometry/sign convention shown. Step 3: On simplification the result is f₁ > f and f₂ become negative. Therefore the correct option is D.