## PHYS208 Fundamentals of Physics II

### Answer for Ch. 24, 31P

Consider a gaussian cylinder of radius *r* and length *L*.
The charge enclosed by the cylinder is *rho* (*pi r*^{2} L) and the flux through the tube wall is *E* (*2 pi r L*).
There is no flux contribution from the endcaps.
By Gauss's law then the electric field is proportional to the distance from the center and to the charge density.
*E* = (*rho r*) / (*2 ep*_{0}), pointing inward.

Outside the cylinder
a "line of charge" result is obtained.

Thanks to Andrew Field for pointing out a correction to the statement on charge enclosed and to Leslie Rossman for pointing out a missing division sign.

"http://www.physics.udel.edu/~watson/phys208/exercises/answers/24-31P.html"

Last updated Oct. 5, 1997.

Copyright George Watson, Univ. of Delaware, 1997.