hw5.dvi
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Modern Physics - Fall XXXXXXXXXXAssignment #5
Due by 12:30 PM on October 7, 2020
1. The cosmic microwave background as a blackbody: The universe is filled with thermal radiation,
which has a blackbody spectrum co
esponding to the temperature T = 2.7K. (a) At what
wavelength λmax is the spectral radiance RT (λ) maximized? (b) At what frequency νmax is RT (ν)
maximized? (c) What is ∆λ = λmax − c/νmax?
2. Photoelectric effect: Platinum (Pt) has the largest work function of any metal: φ ≃ 5.6eV. (a)
What is the maximum wavelength of light which can produce emission of photoelectrons with a
kinetic energy K = φ? (b) In which part of the electromagnetic spectrum (microwave, infrared,
visible, etc.) is this light? (c)What are the answers to (a) and (b) for photoelectrons withK = 100φ?
3. Rutherford scattering: A beam of alpha particles with kinetic energy Kα is fired at a lead foil of
thickness t. What is the maximum Kα(t) for which half the particles scatter through angles greate
than 10◦, i.e. the maximum Kα(t) for which P (θ > 10
◦) ≥ 1/2?