A photoelectric cell is illuminated by a small bright source of light placed at $1 m$ . If the same source of light is placed $2 m$ away, the electrons emitted by the cathode

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each carries one quarter of its previous momentum.

each carries one quarter of its previous energy

are half the previous number.

are one quarter of the previous number.

answer is D.

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Detailed Solution

Intensity of light (I) at a distance d from its source, $I \propto \frac{1}{d^{2}}$ .

On doubling the distance the intensity becomes one fourth i.e. only one fourth of photons now strike the target in comparison to the previous number. Since photoelectric effect occurs due to interaction of a single photon with a single electron, only one-fourth photoelectrons are emitted out of the target.

The frequency of the photons and therefore the kinetic energy and momentum of emitted photoelectrons are same at any distance.

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