Parallel Plate Capacitor Diameter

1. Jan 27, 2014

tomizzo

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

Two circular disks spaced 0.50 mm apart form a parallel-plate capacitor. Transferring 1.70 ×109 electrons from one disk to the other causes the electric field strength to be 3.50 ×105N/C.

What are the diameters of the disks?

2. Relevant equations

Refer to attachment

3. The attempt at a solution

So I substitute everything into the formula and end up getting R = .5 mm. I then double this to find the diameter and still get the wrong answer. Any ideas?

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2. Jan 27, 2014

Staff: Mentor

Not sure what you're intending to do with that equation you attached. It looks like the on-axis field for a charged circular disk at some distance z from the disk along the axis. But here you have a parallel plate capacitor and the field will be (essentially) uniform between the parallel plates.

Look instead to formulas related to parallel plate capacitors.

3. Jan 27, 2014

lightgrav

convert Q to Coulombs, then use Gauss to obtain Area.