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

Explanation

Here , `f=(2)/(3)` and ` R_1=R and R_2=-R`
`therefore` Using the formula,
`(1)/(f)(mu-1)((1)/(R_1)-(1)/(R_2))`
` (1)/((2)/(3)R)=(mu-1)((1)/(R)-(1)/(-R))`
` (3)/(2R)=(mu-1)((1)/(R)+(1)/(R))rArr (3)/(2R)=(mu-1)xx(2)/(R)`
`(3)/(2)=2(mu-1)rArr (3)/(4) =mu-1rArr =(3)/(4) +1`
` mu=(7)/(4)=1.75`