# Homework Help: Problem Set Three

1. Mar 1, 2010

### Shackleford

4. An electron entering Thomson's e/m appartus has an initial velocity of 0.50 x 10^7 m/s. Lying around the lab is a permanent horseshoe magnet of strength 1.3 x 10^-2 T, which you would like to use. (a) What electric field will you need in order to produce zero deflection of the electrons as they travel through the apparatus? (b) The length of nonzero E and B fields is 2.0 cm. When the magnetic field is turned off, but the same electric field remains, how far in the vertical direction will the electron beam be deflected over this length?

For (b), I'm a bit uncertain in using length as the adjacent side in using tangent.

20. (a) At what wavelength will the human body radiate the maximum radiation? (b) Estimate the total power radiated by a person of medium build (assume an area given by a cylinder of 165-cm height and 13-cm radius).

34. What is the threshold frequency for the photoelectric effect on lithium (W = 2.93 eV)? What is the stopping potential if the wavelength of the incident light is 400 nm?

48. If a 6.0-keV photon scatters from a free proton at rest, what is the change in the photon's wavelength if the photon recoils at 90 degrees?