## PHYS208 Fundamentals of Physics II

### Hint for Ch. 24, 20E

a) Consider a gaussian surface which is just outside the inner surface of the spherical shell. E is zero everywhere on that surface.

b) E remains zero on the surface of part a). Can there be any change?

c) E must still remain zero on the surface of part a).

d) What would make them change?

### Hint for Ch. 24, 27P

Use a cylindrical gaussian surface, coaxial with the actual cylinders. Remember that the electric field is everywhere zero in a conductor.

### Hint for Ch. 24, 53P

At all points where there is an electric field it is radially outward. For each part of the problem use a spherical gaussian surface, centered about the center of the actual spheres, and passing through the point where the field is to be found.

a) Charge enclosed is q (r/a)3 for r < a.

b) Charge enclosed is q for a < r < b.

c) The shell is conducting.

d) Charge enclosed is zero.

e) For b < r < c , the electric field must be zero; a gaussian sphere with this radius must enclose no net charge.

### Hint for Ch. 25, 77E

a) So what exactly does the conducting wire do when it joins the other two conductors -- think electrostatics!

b) Use the result for the potential on a spherical conductor, V = kq/R.

c) Use the results of part b) for each sphere.

"http://www.physics.udel.edu/~watson/phys208/exercises/hints/0306.html"
Last updated March 5, 1998.
Copyright George Watson, Univ. of Delaware, 1997.