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Dual Nature of Radiation and Matter
Effect of Intensity on Photoelectric Effect
1 question from 1 paper, each with its answer.
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Concepts tested
- Intensity and number of photoelectrons
All Questions
2003 AIPMT 1 question
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A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2m then -For a point source, intensity at distance r: $I \propto \dfrac{1}{r^2}$.
When the distance is doubled from 1 m to 2 m, the intensity becomes $\dfrac{1}{4}$ of the initial value.
The number of photoelectrons emitted per second is proportional to the intensity (number of photons falling per second). So the number of electrons emitted becomes a quarter of the initial number.
The energy of each photoelectron depends only on the frequency of light ($KE_{max} = h\nu - \phi$), not on intensity, so it does not change.
So the number of electrons emitted is a quarter of the initial number.