Question

If focal length of a plano-convex lens is 20 cm and m = 1.5 then radius of curvature of curved surface is –

• A. 20 cm
• B. 10 cm
• C. 25 cm
• D. 15cm

Answer 1

Answer: (B)

10 cm

Answer 2

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

$\frac { 1 } { + 20 }$ = (1.5 – 1) $\left( \frac { 1 } { \mathrm { R } } - \frac { 1 } { \infty } \right)$

\ R = 10 cm