# Homework Help: Find Vemf

1. Sep 25, 2010

When a battery is connected to a 110.-ohm resistor, the current is 3.98 A. When the same battery is connected to a 400.-ohm resistor, the current is 1.11 A.

Find the emf supplied by the battery and the internal resistance of the battery.

Equations:

Vemf = i*R

I'm not sure how to approach this since you get two voltages (438.7 and 444) from the different resistors.

Should I treat these resistors like they are in the same circuit? In series or in parallel?

2. Sep 26, 2010

### collinsmark

Yes, you'll get two different voltages, by using different resistors, because there is another resistance involved that is always there: the internal resistance of the battery.

(By the way, check your math regarding the voltages you calculated.)
Not the 110 and 400 Ω resistors, no.

But the battery's internal resistance is always there, so yes, the internal resistance is within the circuit in both cases.
What do you think? (Hint: look in your textbook for "internal resistance" of a battery, and the answer should be clear.)

3. Sep 26, 2010