In a device (figure 30-6) that is used to measure the maximum kinetic energy of
ID: 1557810 • Letter: I
Question
In a device (figure 30-6) that is used to measure the maximum kinetic energy of photoelectric effect electrons, the voltage difference between the collector and emitter is increased until the current flowing through the circuit goes to zero. This is called the stopping potential and the KE_max can be very simply calculated if you use electron-volts. Using this device, you measure this voltage to be 0.710 V for electrons emitted from a surface illuminated by 4.92-nm light. Then, when you change the incident light to a new wavelength value, the new voltage is 1.41 V. a) What is this new wavelength? b) What is the work function for the surface?Explanation / Answer
(A) Kmax = 0.710 eV
Energy of photon = h c / lambda
= 1240 eV-nm / 492 nm
= 2.52 eV
Work function of metal = 2.52 - 0.710
= 1.81 eV
Energy of new wavelength = 1.81 + 1.41 = 3.22 e V
wavelength = h c / lambda
= 1240 eV-nm / 3.22 eV
= 385 nm
(B) Work function = 1.81 eV