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प्रश्न
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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उत्तर
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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Use Einstein's photoelectric equation to show how from this graph,
(i) Threshold frequency, and
(ii) Planck's constant can be determined.
Radiation of frequency 1015 Hz is incident on three photosensitive surfaces A, B and C. Following observations are recorded:
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Surface B: photoemission occurs but the photoelectrons have zero kinetic energy.
Surface C: photo emission occurs and photoelectrons have some kinetic energy.
Using Einstein’s photo-electric equation, explain the three observations.
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Einstein proposed that light energy is absorbed in discrete packets called what?
In \[E=h\nu\], what does \[\nu\] represent?
What does \[\phi_0\] represent in Einstein’s photoelectric equation?
Which expression gives stopping potential \[V_0\] in terms of frequency?
