A concave-convex glass lens has refractive index 1.5 and surface radii 30 cm and 20 cm as shown in the original figure. Its concave surface is filled with a liquid of refractive index 1.3. the focal length of the liquid-glass combination is:
Options

Question

A concave-convex glass lens has refractive index 1.5 and surface radii 30 cm and 20 cm as shown in the original figure. Its concave surface is filled with a liquid of refractive index 1.3. the focal length of the liquid-glass combination is:

Options

G1 Physics · Accepted Answer

Using the surface-power calculation exactly as presented in the source solution, the two contributions are combined as 1/f = 0.3/30 + 0.5/60. Therefore, 1/f = 1/100 + 1/120 = (6+5)/600 = 11/600 cm⁻¹. Hence, f = 600/11 cm. Correct option: D.