Grade 12 University Physics
Tutorial 6
1. A metal used in the photoelectric effect has a work function of 2.37 electron volts. Light of wavelength
1000nm, 500 nm and 50 nm is incident on the metal.
a) Calculate the threshold frequency for the metal
b) Calculate the wavelength of the radiation that corresponds to the threshold frequency
c) Calculate the maximum kinetic energy and the speed of the electron when radiation with a wavelength of
1000nm, 500 nm and 50 nm is incident on the metal
2. An x-ray is fired on a metal in an experiment that is studying the Compton effect. The x-ray has a
frequency that initially corresponds to a frequency of 2.857x1018 Hz. The scattering angle is 180 degrees,
meaning that the x-ray bounces right off of the electron and reverses direction (see helpful hints before if
you are struggling with c and d).
a) Calculate the initial wavelength of the x-ray
b) Show that the equation for energy conservation can be written as
hc/wavelength1= hc/wavelength2 + 0.5me Ve22
c) Show that the equation for the conservation of momentum can be written as
h/wavelength1= -h/wavelength2 + meVe2
d) Solve for the wavelength of the x-ray after the collision and the speed of the electron after the collision
Answers:
b) 524 nm
c) NA (no ejected electrons), 1.84x10–20 J (0.115 eV) 2.01x105 m/s,
1 a) 5.72x1014 Hz
3.60x10-18 J (22.5 eV) 2.81x106 m/s
2 a) 105.0x10-12 m
d) 109.8x10-12 m, 1.355x107 m/s