Answer
See answers.
Work Step by Step
At the threshold wavelength, the KE of the photoelectrons is zero, because they barely make it out of the material. Calculate the work function, which equals the energy of the incoming photon.
Use equation 27–4, E = hf, to find the energy of a photon. For electromagnetic radiation, we also know that $f=c/\lambda$.
$$W_o=hf-KE_{max}=hf-0=\frac{hc}{\lambda}-0=\frac{1240 eV\cdot nm}{340nm}=3.647eV$$
a. Use equation 27–5b with the work function we just found. Calculate the maximum kinetic energy of the photoelectrons emitted by 280-nm light.
$$KE_{max}=hf-W_o=\frac{hc}{\lambda}-W_o=\frac{1240 eV\cdot nm}{280nm}-3.647eV=0.78eV$$
b. The wavelength of 360 nm is greater than the threshold wavelength of 340 nm. The photon energy is less than the work function. No electrons are ejected.
