Calculating Electromotive Force in a Circuit

[joel amos]

Homework Statement

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?

Homework Equations

V = ε - IR

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?

 

[sandy.bridge]

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

 

[joel amos]

Not positive, but pretty sure.

 

[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.

 

[joel amos]

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

 

[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".