A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then-
- each emitted electron carries one quarter of the initial energy
- number of electrons emitted is half the initial number
- each emitted electron carries half the initial energy
- number of electrons emitted is a quarter of the initial number
The Correct Option is D
Solution and Explanation
When the source of light is shifted from 1 meter away to 2 meters away, the intensity of the light decreases with the square of the distance according to the inverse square law. Therefore, the intensity of the light at 2 meters is one-fourth of the initial intensity at 1 meter.
The photoelectric current is directly proportional to the intensity of the incident light. If the intensity of the light is reduced to one-fourth, the number of emitted electrons (photoelectric current) will also be reduced to one-fourth.
So, the correct option is (D): number of electrons emitted is a quarter of the initial number
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Concepts Used:
Dual Nature of Radiation and Matter
The dual nature of matter and the dual nature of radiation were throughgoing concepts of physics. At the beginning of the 20th century, scientists untangled one of the best-kept secrets of nature – the wave-particle duplexity or the dual nature of matter and radiation.
Electronic Emission
The least energy that is needed to emit an electron from the surface of a metal can be supplied to the loose electrons.
Photoelectric Effect
The photoelectric effect is a phenomenon that involves electrons getting away from the surface of materials.
Heisenberg’s Uncertainty Principle
Heisenberg’s Uncertainty Principle states that both the momentum and position of a particle cannot be determined simultaneously.