# Homework Help: Electrostatic force problems, help !

1. Feb 8, 2010

### StudentPhys

Electrostatic force problems, help urgent!

1. The problem statement, all variables and given/known data

Question: An isolated hollow metal sphere of radius 40 cm carries a charge of -10*10^-6.
What is the magnitude of the electric field E (a) in the empty space inside the sphere and (b) 60 cm from the center of the sphere ( no picture provided )

2. Relevant equations

Electrostatic force= K * q1*q2/ d^2

3. The attempt at a solution

I´ve tried to use Coloumb´s law to get to the correct answer , what im having trouble to realize is 1. is there even an electric field within a hollow sphere,? and 2. do you count the distance in problem B from the surface of the sphere or from the center? I tried the center , and i got the wrong answer, don´t know if that is the problem. HELP URGENT , test coming up! :O :(

2. Feb 8, 2010

### tiny-tim

Welcome to PF!

Hi StudentPhys! Welcome to PF!

Show us your full calculations, and then we'll see what went wrong, and we'll know how to help!

3. Feb 8, 2010

### StudentPhys

Re: Welcome to PF!

My calculations are as follows:
I went on the assumption, having read it somewhere, that the electric field within a metallic sphere have 0 magnitude. and wrote E=0
and secondly 2) E= (9*10^9)(-10*10^-6)/ (0,6^2)= 32364 N/C

Though the key says these answers are incorrect , is this so or is the key wrong?