# Uniform electrical field - why?

1. Aug 25, 2011

### Nikitin

In a uniform electrical field, why does the field strength remain constant? For a field where two metal plates, one negatively charged the other positively charged, why will E, electric field strength, always remain constant?

If we assume the distance between two plates A & B, where A has a charge of Q and B a charge of -Q, equals 1 meter. then the electrical field strength between them, according to Coloumb's law, would be:

k*Q/(1-n)^2 + k*Q/n^2= k*q/n^2 + k*Q/((n^2) - 2n +1)

where k=8.99*10^9, Q= charge of plates A and B and n= distance from plate A, n=<0,1>

That formula doesn't remain constant for all variables of n.

What exactly is it that I am missing :?

Last edited: Aug 25, 2011
2. Aug 25, 2011

### Staff: Mentor

You can't treat a charged plate as though it were a point charge. You must consider the field from each element of charge across the plate--which involves different distances and angles.

It turns out that the field from an infinite sheet of charge is uniform. Similarly, the field is uniform between two parallel capacitor plates--as long as they are fairly close together and you aren't too close to the edges.

3. Aug 25, 2011

### Nikitin

thank you, I understand!