Question

If the refractive index of a liquid equals that of a glass lens (\[n_1 = n_2\]), the lens maker relation gives \[\frac{1}{f} = 0\]. This means the focal length of the lens becomes:

Options

• Infinite (\[f \to \infty\])

• Equal to the radius of curvature

• Zero

• Negative

Answer 1

If \[n_1 = n_2\], the lens maker relation gives \[\frac{1}{f} = 0\], which means \[f \to \infty\] (infinite focal length). A lens with infinite focal length behaves like a simple plane sheet of glass and does not act like a converging or diverging lens.