The overall aim of the experiment is to investigate the relationship between e.m.f and internal resistance by measuring the variation of current and voltage using a variable resistor
E = I (R + r)
E = IR + Ir = V + Ir
V = –rI + E
Systematic Errors:
Random Errors:
In an experiment, a student uses a variable resistor as an external load. The current flowing through the circuit is measured with a suitable milliammeter and the potential difference across the variable resistor is measured with a voltmeter for a range of resistance values.The data collected was as follows:Plot a graph of these results and determine the e.m.f. and the internal resistance directly from the graph.
Step 1: Plot the data on a graph of V against I and draw a line of best fit
Step 2: Draw the largest triangle possible in order to calculate the gradient
Step 3: Determine the e.m.f. and the internal resistance from the graph
V = –rI + E
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