Investigating the Emf and the internal resistance of a dry cell.

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Wendy Croft 12NB

Investigating the Emf and the internal

resistance of a dry cell

        The objective of this coursework is to find the Emf of the circuit and the internal resistance of a cell. I am going to use this by measuring the resistance (ohms), current (Amps) and voltage (volts) of a circuit.

        The below diagram shows how I am going to set up my experiment:

Apparatus:   Wires


Dry cell


Variable Resistor


By using the variable resistor above, I will measure eleven different readings on an Ammeter and a Voltmeter. I am able to do this as the variable resister measures resistance from 0 to 10 ohms. I will then reverse this procedure by taking the readings from the Voltmeter and the Ammeter when the resistance goes from 10 to 0 ohms. I will do this because by doing this I can view whether or not the original results were reliable. I predict that the results, both ways, will be very close to being the same.

        To make it a fair test, I will make sure that the cell is not left running. I will only have the cell running the time it takes to read the readings off the Voltmeter and the Ammeter. Otherwise the cell would run out and so the results would not be accurate.

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Using my results I will plot a y = mx + c graph so that I can see the relationship between the current and the voltage. I predict that the graph and straight line will look like the one below:

The y-intercept on the graph will be the Emf and the gradient of the line will be the internal resistance of the cell.

        For this experiment I will be using 5amp wire. I will not be using a high current, but if I were to use a current higher than 5 amps then there would be danger ...

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