Question

An equiconvex lens has a power of 5 deoptre. IF it is made of glass of refractive index 1.5. then radius of curvature of its each surface will be?

• A. 20 cm
• B. 10 cm
• C. 40 cm
• D. $\infty$

Answer 1

Answer: (A)

20 cm

Lens make formula
$\frac{1}{f}=(\mu -1)(\frac{1}{R}+\frac{1}{R})$
$5=(1.5-1)\left(\frac{2}{R}\right)$
$R=\frac{0.5\times 2}{5}$
$R=0.2m$
$R=20cm$