Q146 / 150 · MHT CET 2007 · Physics

A photoelectric cell is illuminated by a point source of light $1 \mathrm{~m}$ away. When the source is shifted to $2 \mathrm{~m}$ then

  • A
    each emitted electron carries half the initial energy
  • Correct answer
    B
    number of electrons emitted is a quarter of the initial number
  • C
    each emitted electron carries one quarter of the initial energy
  • D
    number of electrons emitted is half the initial number

Solution

Key Idea Number of photoelectrons emitted per second is directly proportional to intensity of light. Intensity of light source is $$ I \propto \frac{1}{d^{2}} $$ When distance is doubled, intensity becomes one-fourth. As number of photoelectrons $\propto$ intensity, so number of photoelectrons is quarter of the initial number.

Hence, the correct answer is option: 'B'.

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