In an experiment electrons are released with a kinetic energy of 2.8 eV. The amazing physicists doing the experiments are increasing the wavelength by 50%. Do you remember what happens? Are the photoelectrons faster or slower? The energy now is 0.44 eV.
A) Based on that information, what is the material of the cathode?
B) What is the initial wavelength of the light?
C) When you go a few pages back in the textbook you can find out the temperature of a physical object radiating at that wavelength