Threshold wavelength for lithium metal is 6250ËšA. For photo emission, the wavelength of the incident light must be ___________.
A
Exactly equal to 6250˚A
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B
More than 6250˚A
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C
Equal to or more than 6250˚A
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D
Equal to or less than 6250˚A
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Solution
The correct option is D Equal to or less than 6250˚A
The threshold wavelength of a material signifies that if the photons of energy corresponding to this wavelength or higher strike onto the material, they will undergo photo electric effect. As the energy of a photon is inversely proportional to wavelength (E=λhc), the photonic wavelength should be less than equal to threshold wavelength.