Posted by J on .
(a) How many excess electrons must be distributed uniformly within the volume of an isolated plastic sphere 30.0 cm in diameter to produce an electric field of 1150 N/C just outside the surface of the sphere?
(b) what is the electric field at a point 10.0 cm outside the surface?
ok would I use Guass's law for this one? I am lost... and with the 10 cm..where do I put that in the problem?

physics 
drwls,
a) Use Gauss' law.
4 pi R^2 E = N*e/(epsilono)
N is the number of electrons and e is the electron charge in Coulombs.
E is the electric field strangth in N/C
"epsilon zero" = 8.8554*10^12 C^2/N m^2
Make sure R is in meters
b) Use the same equation, but use R + 0.1 m in place of R since you are 10 cm farther away. 
physics 
J,
ok..thank you very much. I thought that is what you would do for part b but I wasn't sure! Thank you!