Chapter 5, Problem 5.136MP

A minimum energy of $7.21\times {10}^{-19}\text{J}$ is required to produce the photoelectric effect in chromium metal.
(a) What is the minimum frequency of light needed to remove an electron from chromium?
(b) Light with a wavelength of $\text{2}{\text{.50×10}}^{-7}\text{m}$ falls on apiece of chromium in an evacuated glass tube. What is the minimum de Brogue wavelength of the emitted electrons? (Note that the energy of the incident light must beconserved; that is, the photon’s energy must equal the sum of the energy needed to eject the electron plus the kinetic energy of the electron.)