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Electricity and Magnetism
 Aim: to measure the Internal Resistance of a Battery The final result will be taken from a graph showing the electrical characteristics of the battery. See Observing the effects of the internal resistance of a battery, The Internal Resistance of a battery Method In the following circuit a bulb is included simply to limit the maximum current. The internal resistance of a battery is not constant but increases as the battery is used. For this reason do not leave the circuit connected longer than is necessary to take the readings. It's also probably easiest to measure the internal resistance of a new battery (or a recently charged battery if you are investigating rechargeable batteries). Most electrical characteristics are plotted with V horizontal and I vertical. This ia based on the logic that the potential difference causes the current to flow (so potential difference independent variable and current dependent variable). However, it is reasonable to suggest that the terminal potential difference of the battery depends on the current we take from it thus we usually plot battery characteristics with I horizontal and V vertical. The equation relating I and V is This is the equation of a straight line of slope -r so we expect a graph looking something like this:

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