Investigate how the length of a piece of wire affects the resistance of a piece of wire.

An Investigation into the resistance of a piece of wire

Aim

The aim of this experiment is to investigate how the length of a piece of wire affects the resistance of a piece of wire.

Introduction

When current goes through a wire, it heats up and is used for appliances that use heat energy e.g. hair dryers, kettles and toasters. The danger is that a wire may become too hot. In this instance, resistance can be used. Resistance occurs when the electrons travelling the wire collide with the atoms of the wire. When they collide, the flow of electrons is slowed down. This causes resistance. Resistance is a measure of how hard it is for the electrons to move through the wire.

Method

Set up the apparatus as shown above.

Once you have set up the apparatus, adjust your wire so the electrons only have 10cm of wire to pass through. Make sure you measure the length accurately with a metre ruler. Then, record the voltage across the wire in volts and the current through the wire in amps. Do the same for the values: 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm and 100cm.

Repeat this experiment twice.

The only thing that we will change in this experiment is the length of the wire.

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The only thing that we will change in this experiment is the length of the wire.

We will try to keep the room temperature constant as this could cause the particles in the wire to move faster and will therefore have an effect on the resistance. The material of the wire must be kept the same as different materials have different levels of conductivity. To keep this experiment as accurate as possible, we must try to make sure that the length of the wire is measured accurately. We must also try to make sure the wire is straight as any bends could affect the resistance of the wire. The readings of the voltmeter and ammeter are taken quickly after the circuit is connected. The reason for this is because when you connect a circuit, current will go through it and the wire will get hotter. We want to readings when heat least affects the investigation and that would be as soon as the circuit is connected.

We calculate resistance from voltage and current data using Ohm’s law. The equation for this would be R (Resistance) = V (Voltage)/ I (Current).

I got this equation from doing an experiment in a lesson where we looked at current and voltage for a resistor.

Prediction

I think that as the length of the wire increases, the resistance will increase too. This is because of the idea of the electrons being resisted by the atoms of the wire. The longer the wire, the more atoms there will be for the electrons to collide with therefore the resistance will be greater. The relationship between the wire length and the resistance should be directly proportional. In a wire twice the length of another piece of wire there would be twice the amount of atoms causing the resistance.

Results

Conclusion

I can see one quite clear trend from the graph and that is, as the wire gets longer, the resistance increases. The graph also shows positive correlation, which proves the above point. The results are also directly proportional. An example of this is when the length of the wire is 50cm; the resistance is 6 ohms and when the length of the wire is 100cm, the resistance is11.9 ohms. This is almost double the size.

The theory behind this is explained in the prediction. In a piece of wire connected to a circuit, there are free moving electrons and atoms in the circuit. The atoms and electrons collide and cause resistance. Resistance happens because the path is made more difficult for both the atoms and electrons to get through. In a wire that is one length, there will be a number of atoms. In a piece of wire twice that length, there will be twice the number of atoms. This will then lead to there being a larger amount of collisions between the atoms and the electrons and therefore the resistance will be higher. This explains why the results were directly proportional.

The results I have collected support my prediction. In my prediction I said that as the length of the wire increased, the resistance would increase and I also said that the results should be directly proportional.

The line of best fit is fairly accurate. Most of the points are either on the line or very close to the line.

Evaluation

I feel that overall my results were fairly accurate. This can be seen when you look at the graph. Only one point was a slight anomaly and that could be down to many reasons.

I did my best to try and make sure the results were accurate. I tried to measure the length of the wire accurately but it wasn’t very practical holding a piece of wire against a metre ruler.

I could have checked the temperature and made sure it was constant so the particles didn’t move more quickly and affect the resistance. The other thing I could have done was to make sure the wire was straight while conducting the experiment as any kinks in the wire may have affected the movement of the atoms and electrons.

I think the cause of the anomalous point was the inaccuracies that could have occurred while measuring the length of the wire.

I think that my results were quite accurate but I think they would have been even more accurate if I had followed the above points