First slide

The lens

Question

The distance between an object and the screen is 100 cm. A lens produces an image on the screen when placed at either of the positions 40 cm apart. The power of the lens is

Moderate

A

$\approx 3 diontres$
B

$\approx 5 dioptres$
C

$\approx 7 diopters$
D

$\approx 9 diopters$

Solution

$f = \frac{D^{2} - x^{2}}{4 D}$ (Focal length by displacement method)
$⇒f= \frac{(100)^{2} - (40)^{2}}{4 \times 100} = 21 cm$
$∴ P = \frac{100}{f} = \frac{100}{21} \approx 5 D$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App