Question

Work function of copper is 4.4 eV. Does copper undergo photoelectric emission by

light of wavelength 6800 A°. (2)

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Answer 1

Given:

Work function of copper is 4.4eV.

To find:

Does copper undergo photoelectric emission by light of wavelength by 6800 A° ?

Calculation:

• Photo-electric emission from a metal surface occurs only when photons (with the energy greater than the threshold energy of the metal) strikes on the surface.

• In other words, photoelectric emission occurs only when electromagnetic waves striking the metal surface have energy greater than the work function.

Let energy of the light be E :

$\therefore \: E = \dfrac{hc}{ \lambda}$

$\implies\: E = \dfrac{6.63 \times {10}^{ - 34} \times (3 \times {10}^{8} )}{6800 \times {10}^{ - 10} }$

$\implies\: E = \dfrac{6.63 \times {10}^{ - 34} \times (3 \times {10}^{8} )}{68 \times {10}^{ - 8} }$

$\implies\: E = 0.2925 \times {10}^{ - 18}$

$\implies\: E = 2.925 \times {10}^{ - 19} \: J$

$\implies\: E = \dfrac{2.925 \times {10}^{ - 19}}{1.6 \times {10}^{ - 19} } \: eV$

$\implies\: E = 1.82 \: eV$

Since , E < work function , hence photo-electric emission will not happen.