Question

The refractive index of a material of a plano concave lens is 5/3, the radius of curvature is 0.3 m. The focal length of the lens in air is:

• A. 0.45m
• B. 0.6m
• C. 0.75m
• D. 1.0m

Answer 1

The correct option is A 0.45m

$\frac{1}{f}=(\mu -1)(\frac{1}{R_1}-\frac{1}{R_2})$
$\frac{1}{f}=(\frac{5}{3}-1)(0-\frac{1}{-0.3})$
$\frac{1}{f}=\frac{2}{0.9}$
$f=0.45m$