In this example involving the photoelectric effect, we'll use the binding energy to calculate the wavelength that corresponds to the threshold frequency. Let's look at our problem. The minimum energy required to eject electrons from a certain metal is 235 kilojoules per mole. Find the longest wavelength in nanometers of electromagnetic radiation that can eject an electron. For this problem, we'll want to use the equation: Binding energy = Planck's constant * threshold frequency Rearranging this equation, we can solve for the threshold frequency. We can use the equation Wavelength = speed of light / frequency to find the corresponding wavelength. We know Planck's constant, and the binding energy is given as 235 kilojoules per mole of electrons. We need to convert this binding energy into joules per single electron to use it in the equation above. First, we can convert from moles of electrons to electrons using Avogadro's number. One mole of electrons is equal to 6.022 * 10^23 electrons. Then, we can convert from kilojoules to joules using the conversion factor: one kilojoule is equal to one thousand joules. If you plug this into your calculator, you should get 3.902 * 10^-19 joules per electron. We can plug these numbers into the equation above to solve for the threshold frequency, and we should get 5.889 * 10^14 one over seconds or Hertz. Now we can solve for wavelength, which equals the speed of light divided by the frequency. Plugging in the speed of light and the threshold frequency, we find that the corresponding wavelength is equal to 5.09 * 10^-7 meters. The question asks for us to state the wavelength in nanometers, so converting this number to nanometers, we get 509 nanometers.