A photoelectric cell is illuminated by a point source of light 1 m away. When the source is taken 2m away
Correct answer: A. The number of electrons emitted is a quarter of the initial number
- A. The number of electrons emitted is a quarter of the initial number
- B. The number of electrons emitted is half the initial number
- C. Each electron emitted carries one quarter of initial energy
- D. Each emitted electron carries half the initial energy
Explanation
When the distance from the light source is doubled, the intensity of light decreases according to the inverse square law. This means that the intensity is reduced to one-fourth of its original value. Since the photoelectric effect depends on the intensity of light hitting the photoelectric cell, the number of emitted electrons also reduces to one quarter of the initial number. Thus, the correct option is that the number of electrons emitted is a quarter of the initial number. The other options are incorrect because they suggest incorrect relationships between distance and the number of emitted electrons or the energy of the emitted electrons, which are not consistent with the principles of the photoelectric effect.
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Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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