Homework Help: Finding electromotive force

1. Feb 28, 2013

joel amos

1. The problem statement, all variables and given/known data
A battery has a current of 3.0A flow through it. It has an internal resistance of 0.039Ω and the circuit has a load of 45Ω.
a) What is the emf?
b) What is the voltage that flows?

2. Relevant equations
V = ε - IR

3. The attempt at a solution
ε = V + IR
ε = (45Ω)(3A) + (3A)(0.039Ω)
ε = 135V + 0.117V

a) 135.117V
b) 135V

I'm new to emf. Does this look correct? If not, can you explain where I went awry?

2. Feb 28, 2013

sandy.bridge

They asked what is the voltage that flows? Are you sure it wasn't current?

3. Feb 28, 2013

joel amos

Not positive, but pretty sure.

4. Feb 28, 2013

sandy.bridge

I would check that. The voltage in a circuit doesn't "flow". The purpose of a battery is to keep the potential difference across two points in a circuit at a specific potential difference.

5. Feb 28, 2013

joel amos

Is part "a" correct? And doesn't current remain constant?

6. Feb 28, 2013

sandy.bridge

Your answer looks good for part a. The current is the same everywhere in a series branch in a circuit. However, current refers to a collection of charges passing through a unit area in time t. Hence, it is often said to "flow".