The threshold wavelength for photoelectric emission from a material is 5200 Å. Photoelectrons will be emitted when this material is iluminated with monochromatic radiation from a (IIT-JEE, 1982)
A
50 W infrared lamp
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B
1 W infrared lamp
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C
50 W ultraviolet lamp
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D
1 W ultraviolet lamp
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Solution
The correct options are C 50 W ultraviolet lamp D 1 W ultraviolet lamp The threshold wavelength is 5200 Å. For ejection of electrons, the wavelength of the light should be less than 5200 Å. so that frequency increases and hence the energy of incident photon increases. UV light has less wavelength than 5200 Å.