Question

The image of an object, formed by a plano-convex lens at a distance of 8m behind the lens, is real and is one third the size of the object. The wavelength of light inside the lens is 2/3 times the wavelength in free space. The radius of the curved surface of the lens is 

(a) 1 m

(b) 6 m

(c) 5 m

(d) 3 m

Answer 1

Correct option is d) 3m 

Explaination:: 

$\mu =\frac{{\lambda }_0}{{\lambda }_m}=\frac{3}{2}$ 

$\frac{1}{f}=\frac{(\mu -1)}{R}=\frac{1}{2R}$ 

$\frac{1}{f}=\frac{1}{V}-\frac{1}{u}$ 

$\frac{1}{8}-(\frac{1}{24})=\frac{1}{2R}$ 

$\frac{3+1}{24}=\frac{1}{2R}$

Comments

R=3
 hence , option d) is correct