- #1

- 1,266

- 11

## Homework Statement

A conducting sphere of radius, R = 5.5 cm with an excess charge of Q = -35.5 nC is surrounded by a concentric, conducting, spherical shell of inner radius, R

_{in}= 9.5 cm and outer radius, R

_{out}= 11.5 cm that carries an excess charge of q = -13.0 nC.

[PLAIN]http://img571.imageshack.us/img571/7821/imagex.gif [Broken]

Determine the electric field at the following radii for the aforementioned arrangement:

**(a)**r = 42.5 cm.

**(b)**r = 8.5 cm.

## The Attempt at a Solution

**(a)**In the indicated region r>R

_{out}. Therefore I model the charge distribution as a sphere with charge -Q and the expression for the field in this region would be

[tex]E=-k_e \frac{Q}{r^2}[/tex]

[tex]-(9 \times 10^9) \frac{35.5}{42.5^2}=176885813.1[/tex]

even if I convert r to meters I still get the wrong answer (correct answer: 2420)

**(b)**Again, I can apply Gauss's law to find the electric field. Since R<r<R

_{in}I think I should use:

[tex]k_e \frac{Q}{r^2}=(9 \times 10^9) \frac{35.5}{8.5^2} = 4422145329[/tex]

The correct answer is 44200 N/C, did I forget to convert something?

Thanks.

Last edited by a moderator: