Question

A biconvex thick lens is constructed with glass $(\mu =1.50)$. Each of the surfaces has a radius of 10 cm and the thickness at the middle is 5 cm. Locate the image of an object placed far away from the lens.

Answer 1

For focal length of given lens

Using lensmaker's formula

$\frac{1}{f}=(\mu -1)(\frac{1}{R_1}-\frac{1}{R_2})$

$=(1.5-1)(\frac{1}{10}-\frac{1}{-10})$

$=0.5\times \frac{2}{10}$

$\Rightarrow f=10\text{cm}$

We know that the image is formed at focus of convex lens when object is at infinity.