# Homework Help: What the! isn't this plug and chug?

1. Oct 26, 2005

### mr_coffee

A car battery with a 12 V emf and an internal resistance of 0.050 is being charged with a current of 60 A.

(a) What is the potential difference V across its terminals?

Okay i have an equation that should work perfectly!!
Points a and b are located at he terminals of the battery, thus the potential difference Vb-Va is the termian to terminal potential difference V across the battery, we see that:
V = EMF - ir. r is the internal resitance of the battery, and they give me 60 amps as the current?
V = (12V)-(60A)(.050) = 9V, which is wrong!

2. Oct 26, 2005

### jsamilo

You are CHARGING the battery, not discharging the battery, so there is no way the resulting voltage would be lower than the nominal voltage...

3. Oct 27, 2005

### mr_coffee

I looked in the book and it gives me no case if ur charging the battery, whats the difference? It also didn't say that the formula i used is only for discharging a battery

4. Oct 27, 2005

### big man

A simple change in sign of the term "ir" maybe??

5. Oct 27, 2005

### mr_coffee

Ohhh!! thanks again bigman!!