Q. Which of the following statements is correct regarding photoelectric effect?
1. The electrons are emitted if emitting surface is at high temperature.
2. Photoemission occurs if wavelength is less than a critical value.
3. The K.E. of photoelectrons is proportional to the square of the amplitude of incident radiation.
4. The photoelectric current is proportional to the frequency of incident radiation.

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Solution:

When the wavelength of incident radiation on the metal surface is less than threshold (critical) wavelength, then photoelectric emission takes place.