Question

The refractive index of a material of plano concave lens

Answer 1

Explanation:

Q. The refractive index of Plano concave lens is 5/3 ,the radius of curvature is 0.3 m. what is the focal length of lens in air..

NOTE :The radius of plane part of concave lens is infinity.

The refractive index of lens is n(l)

The refractive index of air is n(a) =1

Using the lens maker formula :

$\frac{1}{f} = ( \frac{nl}{nm} -1) \frac{1}{r1} - \frac{1}{r2}$

where r2 = infinity , r1 = 0.3 :

$\frac{1}{f} = (\frac{5}{3} - 1) \frac{1}{0.3} - \frac{1}{ \infty }$

$\frac{1}{f} = \frac{2}{3} \times \frac{1}{0.3}$

f = 0.45 m

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