University Physics with Modern Physics (14th Edition)

Published by Pearson
ISBN 10: 0321973615
ISBN 13: 978-0-32197-361-0

Chapter 38 - Photons: Light Waves Behaving as Particles - Problems - Discussion Questions - Page 1275: Q38.9


If $V_{AC}>>\phi$ every photon that encounters an electron will have sufficient energy to liberate it from the surface so the rate of electrons passing the ammeter will be constant. $K>0$ if $eV_{AC} - hf > \phi$, and in the limit of $\phi_{small} $ this becomes $eV_{AC}-hf>(\approx 0)$

Work Step by Step

Recall $eV_{AC} = hf + \phi$, such that $eV_{AC}-hf $ is the photoelectron's kinetic energy and if that energy is greater than the work function $\phi$ the electron will escape the surface. If $V_{AC}>>\phi$ every photon incident on the surface will liberate a photoelectron (above some threshold $f_0$) . In the realm of $V_{AC}>> \phi, \phi$ becomes trivially small and a constant stream of electrons will pass from the surface through the experiment's ammeter, giving a constant current.
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