For a photosensitive surface, threshold wavelength is λ₀. Does photoemission occur, if the wavelength (λ) of the incident radiation is (a) more than λ₀ (b) less than λ₀? Justify your answer.

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Solution

Einstein's photoelectric equation gives us,

hv = {hv}_{0} + \frac{1}{2} {mv}^{2}_{\max}

h \frac{c}{λ} = h \frac{c}{λ_{0}} + \frac{1}{2} {mv}^{2}_{\max}

(a) When,

λ > λ_{0}, \frac{1}{2} {mv}^{2}_{\max}

is negative. Therefore, photoemission will not occur.

(b) When

λ > λ_{0}, \frac{1}{2} {mv}^{2}_{\max}

is negative. So, photoemission will occur.
Here,

λ_{o}

is the threshold wavelength.

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