1. How does one explain the emission of electrons from a photosen… - Vidyadip

Question

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?
The work function of the following metals is given: Na 2.75 ev, K = 2.3 eV, Mo = 4.17 eV and Ni = 5.15 eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 Å from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away?

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Answer

Einstein’s Photoelectric equation is

$hv=\varphi_0+K_{\text{max}}$

When a photon of energy $'hv'$ is incident on the metal, some part of this energy is utilised as work function to eject the electron and remaining energy appears as the kinetic energy of the emitted electron.

$E=\frac{hc}{\lambda}=\frac{6.63\times10^{-34}\times3\times10^8}{3.3\times10^{-7}\times1.6\times10^{-19}}eV$

$=3.77\text{eV}$

The work function of Mo and Ni is more than the energy of the incident photons; so photoelectric emission will not take place from these metals. Kinetic energy of photo electrons will not change, only photoelectric current will change.

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