# Internal Resistance

1. Nov 18, 2005

### Nabbsy88

Hi, Im in yr 11 and i study physics im my free time but have stumnbled across the following question that i cant seem to find an answer for in any books, would someone please be able to help me?

A cell is connected in series with a variable resistor. A high resistance voltmeter is connected across the terminals of the cell. When the variable resistor is set at 13Ohms the voltmeter reads 1.30V. And when the Variable resistor reads 8Ohms the voltmeter reads 1.20V. Find:

A) The emf of the cell
B) The internal resistance of the cell.

Any help at all would be greatly appreciated
Thanks.

2. Nov 18, 2005

### Staff: Mentor

Here's a hint: Treat the cell as being a perfect voltage source in series with a resistance equal to its internal resistance. Note that when you change the resistance in the variable resistance the current flowing throught the cell changes; the current creates a voltage drop within the cell due to the internal resistance.