A photocell is illuminated by a small bright source placed one metre away. When the same source of light is placed two metres away, the electrons emitted by the photo cathode

Each carries one-quarter of its previous energy

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Each carries one-quarter of its previous momentum

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Are half as numerous

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Are one-quarter as numerous

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Solution

The correct option is D Are one-quarter as numerous
Intensity of sources decrease with $r^{2}$
$I n t e n s i t y \propto \frac{1}{r^{2}}$
So, when source is moved $2 m$ away ,it will decrease by $4$ times.

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A photocell is illuminated by a small bright source placed one metre away. When the same source of light is placed two metres away, the electrons emitted by the photo cathode

The correct option is D Are one-quarter as numerousIntensity of sources decrease with r2Intensity∝1r2 So, when source is moved 2m away ,it will decrease by 4 times.

The correct option is D Are one-quarter as numerous
Intensity of sources decrease with $r^{2}$
$I n t e n s i t y \propto \frac{1}{r^{2}}$
So, when source is moved $2 m$ away ,it will decrease by $4$ times.