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Phy 3031 Modern physics, Spring 2008
Homework set week #11. Due at the start of class on Monday, March 24, 2008.
For numerical answers give two significant digits. The first should be correct, the second can
be approximate.
1. A particular radiating cavity has the maximum of its spectral distribution at a wavelength of 29µm = 29 × 10−6 m. The temperature is then changed so that the total
power radiated by the cavity increases by a factor of 4.
(a) At what wavelength does the new spectral distribution have its maximum?
(b) What is the new temperature of the cavity?
2. The work function of molybdenum is 4.22 eV.
(a) What is the threshold frequency for the photoelectric effect in molybdenum?
(b) Will yellow light of wavelength 560 nm eject photoelectrons from molybdenum?
3. The Compton effect has a photon scattering off an electron. This may be observed
with photons of wavelength 0.07 nm.
(a) What is the energy of such a photon?
(b) What is the wavelength of a photon scattered at 180◦ ?
(c) What is the energy of a photon scattered at 180◦ ?
(d) What is the kinetic energy of the electron if the photon is scattered at 180◦ ?
4. For an incident photon of frequency f1 , what is the maximum amount of kinetic energy
that the recoiling electron can gain via Compton scattering? Your answer to this
problem should be a formula.