Problem 5.274

Illuminating the surface of a certain metal alternately with light of wavelengths $\lambda_{1}=0.35 \mu \mathrm{m}$ and $\lambda_{2}=0.54 \mu \mathrm{m},$ it was found that the corresponding maximum velocities of photoelectrons differ by a factor $\eta=2.0 .$ Find the work function of that metal.

A=2 \pi c \hbar \frac{\left(\eta^{2}-\lambda_{2} / \lambda_{1}\right)}{\lambda_{2}\left(\eta^{2}-1\right)}=1.9 \mathrm{eV}

Thermal Radiation. Quantum Nature of Light.