Question

If the lens material and the surrounding liquid have the same refractive index (\[n_2 = n_1\]), then:

Options

• the focal length becomes 1 metre

• \[P = \frac{n_1}{f}\] and the power doubles

• \[P = 0\], so the lens has no focusing power (becomes invisible)

• the lens behaves like a concave lens

Answer 1

When \[n_2 = n_1\], the factor \[(n_2 - n_1)\] becomes zero, so \[P = 0\]. No refraction occurs at the surfaces, the lens has no focusing power, and it becomes invisible in the medium.