# Finding the magnitude?

1. Mar 14, 2015

### littlejon

1. The problem statement, all variables and given/known data
Two 10-cm-diameter charged rings face each other, 25cm apart. The left ring is charged to -17nC and the right ring is charged to +17nC .
A.What is the magnitude of the electric field E⃗ at the midpoint between the two rings?

B.What is the magnitude of the force F⃗ on a -1.0 nC charge placed at the midpoint?
Express your answer to two significant figures and include the appropriate units.

2. Relevant equations
(E1)z=ZQ1/4πε0(z^2+r^2)^(3/2)

3. The attempt at a solution
((9E9)(.10)(-17E-9))/((.10)^2+(.50)^2)^3/2= 2.2E4.
Unfortunately
this is not the answer any help?

2. Mar 14, 2015

### haruspex

You don't seem to have correctly matched up the z and r variables in the equation to the given numbers. What values for z and r have you used?

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