Question

Could someone explain the difference between emf and voltage to me?

I've always used them a bit too interchangably, but that's coming back to haunt me with the equation for AC voltage V=IZ+E

I haven't been able to find any good resources online, and my textbook skips over any definitions

Answer 1

EMF is the work done in taking unit positive charge round a complete electrical circuit.

Voltage which is better called the potential difference between two points in an electrical circuit is the work done in taking unit positive change between those two points.

I am not sure where the equation that you have mentioned V=IZ+E has come from.

Answer 2

Hi @Farcher,

Thanks for the reply. Here's the equation I'm talking about. It's from Electromechanical Motion Devices 2nd Edition by Krause Wasynczuk and Pekarek.

There's really not much other context on the question

Answer 3

Perhaps it's an induced voltage component from the circuit's inductance?

Answer 4

Your question is an interesting one in that it highlights a difference between the approach of some Physicists and Engineers.

These Physicist, quite naturally, want the Phsics to be right and so will say that Kirchhoff's voltage law is invalid if there are changing fluxes and induced emf.
For the sake of convenience Engineers take the practical approach and bend the rules a little to make life easier. They are after the correct solution via the most convenient route.

The equation that you quoted seems to have applied voltage/emf? (V) on the left hand side is equal to voltages across non inductive components (IZ) plus the voltage or is it emf across inductive components. A hybrid equation.

Answer 5

That makes sense. Thanks for the insight @Farcher!