Question

If the distance of 100 watt lamp is increased from a photocell, the saturation current 'i' in the photocell varies with distance 'd' as

• A. $i\alpha d^2$
• B. $i\alpha d$
• C. $i\alpha 1/d$
• D. $i\alpha 1/d^2$

Answer 1

The correct option is D $i\alpha 1/d^2$

According to inverse square law of radiation, Intensity of the radiation varies inversely to square of distance from the source.

$i\alpha \frac{1}{d^2}$

Since, photoelectric current is directly proportional to intensity I

$i\alpha \frac{1}{d^2}$