A symmetric convex lens has refractive index 1.8 and each surface radius 20 cm. It is immersed in a liquid of refractive index 1.5. If P(air):P(liquid) = x:1, find x.

Question

G1 Physics · Accepted Answer

Lens power in a medium is P = (n(lens)/n(medium) - 1)(1/R₁ - 1/R₂). For the same lens geometry, the curvature factor cancels in the ratio. In air: factor = 1.8 - 1 = 0.8. In liquid: factor = 1.8/1.5 - 1 = 0.2. P(air)/P(liquid) = 0.8/0.2 = 4. Final value: 4