Question

Focal length of convex lens is 10 cm and its refractive index is 1.5. If radius of curvature of one of its surface is 7.5 cm, the radius of curvature of other surface is

• A. 7.5 cm
• B. 15 cm
• C. 75 cm
• D. 5 cm

Answer 1

Answer: (B)

15 cm

Answer 2

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

$\frac { 1 } { 10 }$ = (1.5 – 1) $\left( \frac { 1 } { 7.5 } - \frac { 1 } { \mathrm { R } _ { 2 } } \right)$

\ R₂ = 15 cm