Question

A convex lens of power 5D is placed at a distance of 30 cm from a screen. At what distance from the lens should the screen be placed so that its image is formed on the screen?

• A. The screen should be placed at 90 cm from the lens.
• B. The screen should be placed at 30 cm from the lens.
• C. The screen should be placed at 60 cm from the lens.
• D. The screen should be placed at 150 cm from the lens.

Answer 1

The correct option is C

The screen should be placed at 60 cm from the lens.

Power of the lens, P = +5D

$\Rightarrow$ Focal length, f = $\frac{1}{5}$ = 0.2 m = 20 cm

Here, the screen is placed 30 cm from the lens.

Now, v = +30 cm, f = +20 cm, u =?

Using the lens formula, we get u = - 60 cm

Therefore, the screen should be placed at 60 cm from the lens.