Question

The focal length of a convex lens is 10 cm and its refractive index is 1.5. If the radius of curvature of one surface is 7.5 cm, the radius of curvature of second surface will be-

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

Answer 1

Answer: (B)

15 cm

Answer 2

$\frac { 1 } { \mathrm { f } }$ = (m – 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