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# Internal resistance investigation - I will conduct the following investigation with the aim to find the internal resistance of a lemon battery, which I will construct myself.

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Introduction

AS Physics – Internal resistance investigation

I will conduct the following investigation with the aim to find the internal resistance of a lemon battery, which I will construct myself.

The variables that could affect my experiment are as follows:

• Size of lemon – I will conduct my experiment in no longer than an hour, allowing me to use the same lemon for all results
• Size of metal electrodes – I will use the exact same electrodes throughout the whole experiment
• Length of any connecting wires – I will use the exact same wires throughout my experiment and will not break the circuit once I have started collecting data
• Resistance in the circuit – I will vary this using a highly sensitive variable resistor as shown in my method.

To make my experiment fair I will only vary the most relevant variable to what I am investigating, which is the resistance in the circuit. All the other variables will be kept the same throughout the experiment as stated above.

In my experiment I will need to measure the terminal pd, V, and the Current, I (in amps), for many values of resistance, R (in Ω), I will measure these as I know that V=E-Ir so these are the values that I need to know if I am to eventually calculate the batteries internal resistance. I think that to make my

Middle

So the pd, V, available to the rest of the circuit is:

V = E – Ir

Where:        E = the e.m.f. of the cell

I = the current through the cell

And r = the value of the internal resistance

So Ir = the pd across the internal resistor

To find the internal resistance experimentally:

As V = E – Ir, if you plot a graph of terminal pd, V, against current, I, the gradient of the graph will be equal to the internal resistance of the cell.

(From www.s-cool.co.uk/asphysics)

Conclusion

The only other problem I had with my experiment was the slight curve in my graph due to the deterioration of the battery as I was collecting my results. I could have avoided this by taking my results more quickly so the battery had less time to deteriorate and repeating the experiment more times to get a better average. This deterioration must have also greatly affected the margin of error in my experiment so I should have really thought about this more before I started taking my results.

Because the battery deteriorates so quickly, this limits the amount of time that you can collect data without the results becoming more inaccurate, so repeating my experiment twice with the same lemon and electrodes probably also limited the accuracy of my experiment.

Next time I would take more results more quickly and be more organised to make my results and conclusions more accurate. I could also investigate this topic further by using different substances for my electrolyte like different fruit juices or acids. I could also try using different materials for the electrodes and see how that affected the internal resistance

I have completed my aim to find the internal resistance of my self-constructed lemon battery and found the internal resistance to be 5909.1 Ω.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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