johnwandering

7+ Year Member
May 18, 2009
430
6
Status
The electric field across a capacitor equation is

E=V/d=(V-IR)/L

I was wondering what the line V-IR meant. It clearly represents 2 different voltages, so I assume IR refers to the circuit voltage. I was wondering what voltage the V variable stood for.


Also, does this apply for general electric fields, or just capacitors?
 
May 9, 2012
19
0
Status
Pre-Medical
(V-IR)/L would apply if you had a resistor in series with the capacitor. The V represents the voltage of the EMF, and IR would represent the voltage difference across the resistor. Thus, the voltage across the capacitor would be V-IR, making the second equation equivalent to the first.

E = V/d applies only to electric fields generated by infinitely parallel plates (like capacitors). The formula for electric fields created by a point charge, shell, or sphere is E = kq/r^2.
 
May 9, 2012
19
0
Status
Pre-Medical
You subtract the voltage over the resistor from the EMF because that's the voltage difference over the capacitor. Note that this equation only works for a resistor in series with a capacitor (in parallel, they would receive the same voltage).