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Electrons and Photons- Short Question-Answers
1. What is threshold frequency?
Ans. There is a certain minimum frequency of radiation below which there is no photoelectrice emission whatever be the intensity of radiation. This minimum frequency is called the should frequency. Different metals have different threshold frequencies. Illumination of a surface with light of frequency less than threshold frequency will not cause photoelectric emission.
2. Explain why photoelectric effect cannot be observed with all wavelengths of light.
Ans: Each metal surface has a work function (W-=hf0) which is the minimum energy required to eject an electron from an atom of its surface. So, the light photo must have at least energy which is equal to work function of the metal in order to eject an electron from its surface. If the energy of the incident photon is less than the work function of the metal then there will not be ejection of any electron. Since the energy of photo in only frequency- dependent (E=hf), only a particular wavelength of light can eject electron. So photoelectric effect is not observed with all wavelength of light.
