A biconvex lens has focal length `(2)/(3)` times the radius of curvature of either surface. Calculate refraction index f material of the lens.

Answer

`1.75`

Explanation

Here, `f = (2)/(3)`, where `R_1 = R, R_2 = -R = -R, mu = ?`
From `(1)/(f) = (mu - 1)((1)/(R_1) - (1)/(R_2))`
`(3)/(2 R) = (mu - 1) ((1)/( R) + (1)/( R)) = (mu - 1) (2)/( R)`
`mu - 1 = (3)/(4) = 0.75, mu = 1.75`.