1. A solid sphere has a charge density given by ρ=Kr³ where the constant K=6.50x10^-3C/m⁶. The radius of the sphere is 0.35m. Find the magnitude of the electric field E at (a) r=0.20m and (b) r=0.80m. Hint: dV_sperical=4πr²dr. Note: This is the standard Gauss' Law problem with a spherically symmetric charge distribution. You should be able to work this for just about any spherically-symmetric form for ρ. Some people might even find that they can make up different powers for this ρ and rework the problem over and over and over...
2. problem 4.19
3. problem 4.20 You're using the vector equation J=nqv so you do put in your signs here. Note that (a) negative charges moving e.g. to the left are the same as positive charges moving to the right, and (b) this is vector addition so use your components.
4. Suppose that tin (Sn) donates 2 of its electrons to the conduction band of electrons while a current is flowing through it.
   (a) Find the number density 'n' of these conduction electrons in units of #/m³. A very useful web page for this part is http://webelements.com/.
   (b) Find the drift velocity v of the electrons in a tin wire of radius r=0.120cm, with a current of 2.75Amps (watch your units!) flowing through it.

   That's all for homework #5.