I assume that this was a science class dealing with electricity and batteries?

Perhaps you did an experiment where you took a 1.5V battery, connected it to a variable external resistance, and measured the current and/or voltage across the external resistance (sometimes called the load resistance)?

The question would then be to estimate the internal resistance of the battery.

There are a lot of variables in this experiment, but if you

*assume * that the internal resistance is a

*constant * resistance, then it becomes much easier to find an answer.

You can simplify the electrical behaviour of a battery to being an "ideal" voltage source in series with a constant resistor.

- Measuring the voltage of the battery when there is no load tells you what the internal voltage is (because there is effectively no current flowing through the internal resistance).

- Measuring the voltage of the battery when there is an external resistance allows you to estimate the internal resistance. The internal resistance forms a voltage divider with the external resistance.

The equation is here:

http://en.wikipedia.org/wiki/Internal_resistance#Batteries(If you took several measurements with different settings of the external resistance, you can plot them on a graph of current vs voltage, and try to draw a line through the points.)