Question

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

Answer 1

$R_1=R_2=10cm$, $t=5cm,u=-\infty$

For the first refraction, (at $A$)

$\frac{{\mu }_g}{v}=-\frac{{\mu }_a}{u}=\frac{{\mu }_g-{\mu }_a}{R_1}$ or $\frac{1.5}{v}-0=\frac{1.5}{10}$

$\Rightarrow v=30cm$.

Again, for 2nd surface, $u=(30-5)=25cm$ (virtual object)

$R_2=-10cm$

So, $\frac{1}{v}-\frac{15}{25}=\frac{-0.5}{-10}$

$\Rightarrow v=9.1cm$

So, the image is formed $9.1cm$ further from the 2nd surface of the lens.