## 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 electro*statics*!

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.