# Electric field between two conducting plates of different potential?

not sure if this question's been asked before, though I couldn't see one in my brief search on here... Well, the problem I am trying to solve is that I want to determine the electric field strength between two parallel rectangular-shaped plates with different voltages on each plate. For example, rectangular plate 1 has a voltage of +180V and rectangular plate 2 (parallel to plate 1) has a voltage of -5V. What equation(s) could we use to determine the field strength at any point between these two plates? The distance of separation of the plates is finite, say 8.6mm.

• A hint: the electric field strength can be expressed in units V/m.. – BjornW Jul 28 '11 at 7:49
• What level of response do you want? Are you trying to account for edge effects, or do you just want to imagine infinite plates? In that case the electric field is constant. – Mark Eichenlaub Jul 28 '11 at 9:33
• A simple response is a great response! I found out the answer E=V/d. I wasn't sure if the field E was going to be uniform if the voltages of the two plates are not equal and opposite. But, yes it looks like E=V/d works irrespective of whether the voltages on the plate is equal or non-equal. Thanks for your help! :) – Rhea Jul 28 '11 at 22:14

## 1 Answer

If you are not worried about fringing effects near the edges of the plates (which you shouldn't, if the plate dimensions are much larger than the gap distance), then finding the field is simple: V/d, where V is the voltage between the plates and d is the gap distance between the plates.

So, in the example you gave, there would be a field of 185V/(0.0086m) = about 21512 V/m, between the two plates. The voltage 1mm from the -5V plate would be -5 + (0.001m)(21512 V/M) = 21.512V-5V = 17.512V

• Why is 185V instead of 175? – MGZero Jul 28 '11 at 21:59
• Because it is the voltage difference i.e. 180-(-5)=185 – Rhea Jul 28 '11 at 22:16
• Oh, I see, I was adding them for whatever reason. Yea, that would make more sense. – MGZero Jul 29 '11 at 14:07