# I About uniform electric field between parallel plates

1. May 13, 2017

### curiosity colour

I have learned that the electric field between parallel plates are independent of distance
since E=V/d
so if I increase the distance between parallel plates, the E will decrease, right?
if I am right on the previous statement, then why does the electric field are independent of distance?

2. May 13, 2017

### Staff: Mentor

Are you sure that isn't for ideal infinitely long parallel plates?

3. May 13, 2017

### Math_QED

You are right. This is only for such plates and can be derived using Gauss' law. If we neglect rand effects, we can still use it as an approximation for smaller plates, though.

4. May 13, 2017

### curiosity colour

The textbook just wrote parallel plates, didn't said anything about ideal infinitely long parallel plates
So only if parallel plates are infinitely long, the electric field between parallel plates are independent of distance ? Still though, why is that?

5. May 13, 2017

### Math_QED

Do you know Gauss' law? (one of the maxwell equations, $\iint_S \vec E . \vec{dA} = \frac{Q_{enc}}{\epsilon_0}$ where we integrate over a closed surface $S$)

6. May 13, 2017

### curiosity colour

Yeah, I know about Gauss's law

7. May 13, 2017

### sophiecentaur

If the plates are insulated, the Potential difference will change as you separate them so the V in "E=V/d" will change. (The Capacitance C will change and V=Q/C applies)
If you connect a source of PD to the plates, to maintain V then E=V/d will apply. So there is no contradiction.

8. May 13, 2017

### Staff: Mentor

The E field is independent of the distance, but the voltage is not. The E field is the gradient of the voltage, so if you have the same E field over a larger distance then you have a greater voltage.