Measuring Internal Resistance

The experiment has no dangers except for when I am going to test the car battery because the power it supplies might be too much and cause a fire. To avoid this happening I am going to keep the resistance quite high.

To improve accuracy with the dry cell I am going to use 4 dry cells and take the average, also with all the sources I am going to try and get a wide range of results at least 7 measurements for each.

I am going to record my results in a spreadsheet and then create graphs showing voltage against current using this data. When creating graphs for my results, I am going to include error bars where the error margin will be 5% so that slight errors in reading my results and accuracy in the equipment are accounted for. I will then draw a best-fit line so that I can work out the internal resistance by calculating the gradient.

The gradient shows me the internal resistance because:

Lost p.d./current = internal resistance

I have shown below how this is true:

The line AB represents the lost p.d. and the line BC represents the current. The line AC shows AB/BC, which is the same as the internal resistance.