1) The maximum kinetic energy of photoelectrons is 2.8eV. When the wavelength of the light is increased by 50%, the maximum energy decreases to 1.1 eV. What are the "work function" of the cathode and the "initial wavelength"? K.E.initial=K.E.max=2.8eV=4.48x10^-19J lambda.final=1.5*lambda.initial Final energy = 1.1 eV (<---is this purely kinetic energy? why?) K.E.max = hc/(lambda.initial) - work function But now I have 2 unknowns: work function and lambda.initial, what can I do to solve for both? I am stuck here... Does anyone have any idea or insight? Any help is greatly appreciated.

But you can state 2 equations: 2.8ev = hc/lambdai -w 1.1ev = hc/(1.5*lambdai) -w w is the same in both equations, the ionization energy for the cathode. Between the two equations solve for either lambdai or w, then plug that result into either equation to solve for the remaining. Simple algebra. Please Register or Log in to view the hidden image! >>edit Of course you need to use consistant units of measurement.