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Question
The photon emitted during the de-excitation from the first excited level to the ground state of a hydrogen atom is used to irradiate a photocathode in which the stopping potential is 5 V. Calculate the work function of the cathode used.
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Solution
In the photoelectric effect, stopping potential is directly proportional to the maximum kinetic energy of the emitted electron.
This maximum kinetic energy is further dependent on the frequency of incident light as well as the work function of the cathode. Combining both these facts, we can arrive at the work function of the cathode used.
KE = hν - Φ0
Where, hν = E2 - E1
= `(-13.6)/2^2 - (-13.6)/1^2`
= `3/4 xx 13.6 = 10.2` eV
eV = hν - Φ0
`5V xx e = 10.2 eV - phi_0`
Φ0 = 5.2 eV
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