Physics 308 Homework
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Homework #8: Due Saturday, March 29, by 12:00noon.

  1. A proton with KE=1.0x1016eV is moving perpendicular to an interstellar magnetic field. The radius of curvature of the proton's path is 11 light years (1 light year is the distance light travels in 1 year). (a) What is the strength of the interstellar magnetic field? (b) How long in years does the proton take to make one complete revolution? (c) How long does it take for the proton to radiate away 20% of its original KE (you may assume the power is approx. constant over this time period)?
  2. A wire has within it a current density given by J=J0r3z where the boldface z is the z unit vector, and J0=2,500Amp/m5. This will make the current bunch up towards the edges of the wire. The radius of the wire is 0.20cm. Find (a) the magnitude of the magnetic field at a distance of 0.12cm from the axis of the wire, and (b) the magnitude of the magnetic field at a distance of 0.35cm from the axis of the wire.
  3. A hollow wire has within it a current density given by J=J0r3z where the boldface z is the z unit vector, and J0=2,500Amp/m5. The radius of the hollow part of the wire is 0.10cm; the radius of the wire itself is 0.20cm. Find (a) the magnitude of the magnetic field at a distance of 0.12cm from the axis of the wire, and (b) the magnitude of the magnetic field at a distance of 0.35cm from the axis of the wire.
  4. Refer to fig. 6.43 on p. 334 for this problem. Find the strength of the magnetic field at (a) a point 2.5cm above point P, and (b) 6.0cm above point P.
  5. For this problem, the positive x-direction is out of the page, the positive y-direction is to the right of the page, and the positive z-direction is to the top of the page. Three wires are lying on a horizontal surface. All three have the same radius of 1.0mm=1.0x10-3m. They are insulated and are touching. The middle wire is lying at the origin (x,y,z)=(0,0,0). Each has a current of 2.50A running into the page, in the negative x-direction. Find the magntide and direction of the net magnetic field at the following points: (a) (0,0,0) (b) (0,8mm,0) (c) (0,0,25mm) Hint: Perhaps you can make a simplyfying approximation on this one and explain in writing this approximation, that will make your life easier.
   That's all for homework #8.