The radii of curvature of a double convex lens are 15 cm and 30 cm and its refractive index is 1.5 t

Question

The radii of curvature of a double convex lens are 15 cm and 30 cm and its refractive index is 1.5 then its focal length is

Professor PC Thomas Classes · Answer

Lens maker's formula: $\frac{1}{f} = (\mu - 1)(\frac{1}{R_1} - \frac{1}{R_2}) = (1.5 - 1)(\frac{1}{15} - \frac{1}{-30}) \implies f = 20 	ext{ cm}$.