Question

A biconvex lens has a focal length 2/3times the radius of curvature of either surface. The refractive index of the lens material is :

• A. 1.75
• B. 1.33
• C. 1.5
• D. 1.0

Answer 1

Answer: (A)

1.75

Answer 2

: $\frac { 1 } { \mathrm { f } } = ( \mu - 1 ) \left( \frac { 1 } { \mathrm { R } _ { 1 } } - \frac { 1 } { \mathrm { R } _ { 2 } } \right)$

Here,

$\mu - 1 = \frac { 3 } { 4 } = 0.75$

$\Rightarrow \mu = 17.5$