Photoelectric effect example: work function in eV and stopping potential for a given wavelength.
In this photoelectric effect example, we are given the longest wavelength of light that will produce a current when there is no stopping potential. We want to determine the work function in eV (binding energy) for the metal target and stopping potential for a given wavelength that is shorter that the threshold wavelength.
We start by calculating the energy of the photons with the maximum wavelength to bump electrons off the metal target. We simply apply E=hc/lambda, plug in hc~1240eVnm and lambda, and we've got the energy of the photons. This is the minimum energy to release electrons from the target, and that's the binding energy (work function)!
Next, we switch to a shorter wavelength and determine the stopping potential for electrons bumped off the target. We start by computing the energy of the photons, and we compute the kinetic energy of an electron in eV headed straight for the opposite plate. We arrive at a kinetic energy in eV. The units make it simple to compute the stopping potential: the same number of volts will do the job, since the charge moving through the potential difference is an electron! At this stopping potential, an electron headed straight for the opposite plate will lose all its kinetic energy to electric potential energy and be repelled from the opposite plate before completing the circuit.
