Question

The "work function", or the minimum energy needed to eject an electron from the metal, can be expressed in several different ways. As stated on the applet page, sodium has a work function of 2.75 eV. In class, we discussed how to determine what that work function was in terms of the wavelength of the light, and found that light of 450 nm was sufficient to eject an electron.

A.)What is the work function for cesium in nm?

b.)For a silver electrode (hint: click just below the word "cesium"), what is the maximum energy of an electron ejected by light of 250 nm? (answer in eV)

Answer 1

A) You are going to have to look up the work function in V before you can calculate the maximum allowed wavelength. It is about 1.9 V. Knowing the value for sodium won't help.

B) Calculate the energy associated with a 250 nm (ultraviolet) photon, using
E = hc/(wavelength)
Then subtract the work function energy of Cs, which is e*(work function in volts)