SUPPLEMENTARY PROBLEMS

THE PHOTOELECTRIC EFFECT

PE-1. A sodium vapor lamp emits light whose wavelength is 589 nm. If the total power of emitted light is 6 W, how many photons are emitted per second?

PE-2. An atom absorbs a photon having a wavelength of 375 nm and immediately emits another photon having a wavelength of 580 nm. How much energy, expressed in eV, was absorbed by the atom in this process?

PE-3. What are the a) frequency, b) wavelength, and c) momentum of a photon having an energy equal to the rest energy of an electron?

PE-4. The energy required to remove an electron from sodium is 2.3 eV. Does sodium show a photoelectric effect for orange light where the wavelength = 680 nm?

PE-5. You wish to pick a substance for a photocell operable in visible light. Which of the following will do? (work function in parentheses) tantalum (4.2 eV), tungsten
(4.5 eV), barium (2.5 eV), lithium (2.3 eV).

PE-6. Incident photons strike a sodium surface (W = 2.3 eV) causing photoelectric emission. When a stopping potential of 5 V is imposed, there is no photocurrent. What is the wavelength of the incident light?

PE-7. Lithium has a work function of 2.3 eV. Determine a) the cut off frequency, b) the cut off wavelength for lithium. Sketch a plot of kinetic energy of photoelectrons as a function of c) frequency, d) wavelength.

PE-8. A laser used to spot-weld detached retinas emits light whose wavelength is
633 nm, with a power of 0.5 W, for a duration of 20 ms. a) How much energy is in each pulse? b) What is the energy of one photon? c) How many photons are in one pulse?

PE-9. A photoelectric surface has a work function of 4 eV. What is the maximum speed of photoelectrons emitted by incident light whose frequency is 3 x 10*15 Hz?

KE = hf - W = hc/lambda - W

Last edited 12/26/05

h = 6.6 x 10*-34 J-s
c = 3 x 10*8 m/s
p = h/lambda
m(electron) = 9.1 x 10*-31 kg
1 eV = 1.6 x 10*-19 J
c = f lambda

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