Question

A point object is placed on the principal. axis of a convex lens (f= 15 cm) at a distance of 30 cm from it. A glass plate $(\mu =1.50)$ of thickness 1 cm is placed on the other side of the lens perpendicular to the axis. Locate the image of the point object.

Answer 1

For the lens, f = 15 cm, u = -30 cm

From the lens formula,

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

$\Rightarrow \frac{1}{v}=\frac{1}{f}+\frac{1}{u}$

$=\frac{1}{15}-\frac{1}{30}=\frac{1}{30}$

$\Rightarrow v=30\text{cm}$

$\Rightarrow \Delta f=(1-\frac{1}{15})1$

[since, $u_2=1.5$and t = 1 cm]

$=1-\frac{2}{3}=\frac{1}{3}=0.33\text{cm}$

The image will be formed at 30 + 0.33

= 30.33 cm from the lens on right side.