Physics 342 Exam 1 February 16, 2006
This is a closed book, open notes exam. There are 10 questions worth 10 points each. Write your
solutions on separate paper and show all work. Make sure your name and student ID is on the
cover. You do not have to work the problems in order, but be sure the problem number is clearly
indicated.
Anyone caught accepting or supplying information on this exam will receive an automatic F in
this course and will be subject to dismissal from the university. Work quietly, carefully, and on
your own.
1. Two objects are identical except that one is hotter than the other. Compare how they respond
to identical forces. Explain.
2. An electron has a speed of 0.75c. Find the speed of a proton that has (a) the same kinetic
energy as the electron and (b) the same momentum as the electron.
3. Why does the existence of a cutoff frequency in the photoelectric effect favor a particle
theory for light rather than a wave theory?
4. If the maximum energy given to an electron during Compton scattering is 30 keV, what is the
wavelength of the incident photon?
5. It is observed that α particles (z=2) with kinetic energies of 13.9 MeV and lower (but not
higher), incident on Cu (Z=29) foils, obey Rutherford’s (sin φ/2)-4 law at back angles (180o).
Estimate the nuclear size of copper from this observation, assuming that the Cu nucleus
remains fixed in a head-on collision with an α particle.
6. A photon is emitted from a hydrogen atom that undergoes an electronic transition from the
state n = 3 to the state n = 2. Calculate (a) the energy, (b) the wavelength, and (c) the
frequency of the emitted photon.
7. Is an electron a particle or a wave? Support your answer by citing some experimental results.
8. A monoenergetic beam of electrons is incident on single slit of width 0.50 nm. A diffraction
pattern is formed on a screen 20 cm from the slit. If the distance between successive minima
of the diffraction pattern is 2.1 cm, what is the energy of the incident electrons?
9. An electron and proton of identical energy encounter the same potential barrier. For which is
the probability of transmission greatest, and why?
10. Consider a square well with one finite wall and one infinite wall. Compare the energy and
momentum of a particle trapped in this well to the energy and momentum of an identical
particle trapped in an infinite well with the same width. Include a diagram of the ground state
amplitude.
