# Homework Help: How does emf relate to current, elec potential, & resistance

1. Mar 3, 2016

### PhysicsBoyMan

1. The problem statement, all variables and given/known data

How does emf relate to current, electrical potential, and resistance? Specifically, in the context of the equations I have posted below.

2. Relevant equations

V = IR
where V is electric potential, I is current, and R is resistance.

V = emf - IR

How can V = emf - IR if V = IR ?
Here is another similar example:

R = V/I

R = (emf - V) / I

3. The attempt at a solution

emf seems to be some kind of change to the original electric potential of a circuit. emf - IR seems to calculate ΔV. Am I right about this? As far as I can tell, Ohm's law uses V, not ΔV. When is ΔV useful and when is V useful? Or do I have this all wrong?

Thanks.

2. Mar 3, 2016

### CWatters

I think some context is missing.

Can you draw the circuit for the examples you mention. Are you talking about a battery with internal resistance or a DC motor or ????