Threshold frequency, ν0 is the minimum frequency which a photon must possess to eject an electron from a metal. It is different for different metals. When a photon of frequency 1.0×1015 s–1 was allowed to hit a metal surface, an electron having 1.988 × 10–19 J of kinetic energy was emitted. Calculate the threshold frequency of this metal. Show that an electron will not be emitted if a photon with a wavelength equal to 600 nm hits the metal surface.
Threshold frequency, ν0 is the minimum frequency which a photon must possess to eject an electron from a metal. It is different for different metals. When a photon of frequency 1.0×1015 s–1 was allowed to hit a metal surface, an electron having 1.988 × 10–19 J of kinetic energy was emitted. Calculate the threshold frequency of this metal. Show that an electron will not be emitted if a photon with a wavelength equal to 600 nm hits the metal surface.
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1 Answer
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This is a Long Answer Type Questions as classified in NCERT Exemplar
ANS- For the emission of electrons from metal the frequency of the striking light should be higher than that of its threshold frequency. We have
h ν = hν 0 + K.E
ν 0 = ν - K.E/h ……. (1)
Given
ν = 1015 s -1, K.E = 1.988 X 10-19J
Thus (1) gives
ν 0 = 7 x 1014 s -1
Given
λ = 600 nm
ν = c/ λ = 5 x 1014 s -1
As ν 0 > ν, thus the electrons do not emit.
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