The refractive index of the material of a concave lens is μ. It is immersed in a medium of refractive index μ 1. A parallel beam of light is incident on the lens. The path of the emergent rays when μ 1 > μ is: (a) (b) (c) (d)

Answer: (a). Lens maker's in a medium: 1/f = ((μ)/(μ₁) - 1)(1/R₁ - 1/R₂). For a concave lens the curvature term is negative; with μ₁ > μ the first factor is also negative, so f > 0. The concave lens acts as a converging lens: parallel rays meet at a point on the axis. So the answer is (a).

The refractive index of the material of a concave lens is μ. It is… | JEE Main 2014 (12 Apr, Shift 1)

Q95JEE Main 2014 · 12 APR · SHIFT 1Medium

Spherical Surfaces & Thin Lenses

The refractive index of the material of a concave lens is $\mu$ . It is immersed in a medium of refractive index $\mu$ 1. A parallel beam of light is incident on the lens. The path of the emergent rays when $\mu$ 1 > $\mu$ is:

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Answer: (a)

Lens maker's in a medium: $\frac{1}{f} = \left(\frac{\mu}{\mu_1} - 1\right)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$ .
For a concave lens the curvature term is negative; with $\mu_1 > \mu$ the first factor is also negative, so $f > 0$ .
The concave lens acts as a converging lens: parallel rays meet at a point on the axis.
So the answer is (a).

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