# Electric Field of a Charged Spherical shell

1. Jan 31, 2007

### SamTsui86

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

A solid conducting sphere of radius 2.00 cm has a charge 6.70 µC. A conducting spherical shell of inner radius 4.00 cm and outer radius 5.00 cm is concentric with the solid sphere and has a charge -3.50 µC. Find the electric field at the folowing radii from the center of this charge configuration.

a) r = 3 cm
b) r = 7 cm

2. Relevant equations

E = Q(inside) / (4 * pie * Eo * r^2)

Eo = 8.85 * 10^ -12

3. The attempt at a solution

Q(inside) is just 6.7 uc - 3.5 uc = 3.2 uc

I just plug in r to the equation to solve for E

It's wrong, please give me some hints. Thank You
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jan 31, 2007

### stunner5000pt

that Q inside you calculated...

would you that value of Q in both questions??

remember enclosed charge

3. Jan 31, 2007

### mjsd

Gauss's Law: $$\int_\text{closed surface} \vec E. d\vec S = q_\text{enclosed}/\epsilon_0$$

4. Jan 31, 2007

### SamTsui86

Ohh I understand it now, thank you very much