Physics Q&A: Internal Resistance in Series with Variable Resistor

[Nabbsy88]

Hi, I am in yr 11 and i study physics I am my free time but have stumnbled across the following question that i can't 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.

 

[Doc Al]

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 through the cell changes; the current creates a voltage drop within the cell due to the internal resistance.