To investigate how the length of wire in a current affects the flow of current.

Planning Chris Doddington

Aim

Prediction

I predict that the longer the wire is the lower the current will be. This is because there are more particles in the wire and so a longer wire will have lots more particles in the way, this will reduce the current. So in a short wire the current will be high. Resistance is a part to, the longer the wire the more resistance there is, so less current.

Here is a diagram that shows two wires, short and long. The current has to ‘bounce off’ more positive ions, this causes more resistance and so the current is lower.

Predicted graph

Here is what I believe the shape of the graph will look like when I have my results. This graph shows that the longer the wire the lower the current.

Diagram

Apparatus

Here is a list of the equipment I will be using:

Powerpack

Ammeter

Voltmeter

Wires

Metre rule

Crocodile clips

Thermometer

Nichrome wire

Safety

The experiment can be dangerous if it is not done safely. I will do the following to ensure that I remain safe in the experiment at all times.

Keep the temperature of the wire low so it doesn’t burn. Do this by turning the powerpack off every time I have finish measuring the current.
Use masking tape to attach the wire to the metre rule. This is because if the wire should burn it will burn straight through the masking tape, but if I was to use cello tape the wire would melt the tape and it would give off bad smells.

Scientific Knowledge

Electrons in wire.

When a current is pushed through a wire is gets through by colliding with positive ions in the wire. This is what the diagram shows. But if the wire is longer then resistance lowers the current, this is because the current has to ‘bounce off’ more particles in the wire.

Temperature

If the temperature in the wire is hot then the positive ions will move around more and so this will cause more resistance. If there is more resistance then the current will be lower and this will give me different results.

Numbering and range

The suitable voltage

This is a preview of the whole essay

Temperature

Numbering and range

The suitable voltage

For the voltage I will use two volts, as I believe this is the best voltage in this investigation. I think this because in preliminary work I did if the voltage was too high then the wire would burn. But any lower than two volts and the current reading will be too small and will be harder to use. The preliminary work showed me that two volts wouldn’t burn the wire. If the temperature does get too hot the test will be unfair, as the current readings will be different.

Measurements

I will measure the current readings and temperature every 10cm along the metre rule, this will give me 10 measurements for each run. I will do 3 runs, this means that if one of the experiments goes a bit wrong then I can tell it has gone wrong when I compare it to my other runs.

Method

Here is a step by step method showing how I did the experiment.

The first thing I did was to set up my equipment. This is how to set up the apparatus:

From the powerpack I had a wire going to a crocodile clip, this would be the end that moves along the rule.
The other wire went to the ammeter.
The wire coming out the other side went to the rule of which the end was stationary, a wire then came out of this and I plugged that in to the voltmeter.
The wire from the other side of the voltmeter went to the moving wire, which lead back to the powerpack.

When I plugged in the wire to the powerpack I made sure that I plugged them into DC and not AC.
I then moved the other crocodile clip to 10cm on the rule and made sure the voltmeter was always on 2 volts, I took the reading from the ammeter, then took the reading from the thermometer, and this showed me the temperature of the wire. I did this every 10cm. All the time changing the voltage so the voltmeter always read two.
When I had finished the first run I did all the measurements again. I took the equipment apart and then put it back together, see why in fair testing.
When I finished run two I did the same again and did a third run.
I put all my results on to a table and calculated the average.

Fair testing

For this experiment I had to make sure it was fair or my results would be wrong. Here is how I made it a fair test:

Temperature was kept low: I did this by using a low voltage and I turned the powerpack off after every reading so it wouldn’t too hot. If the temperature get too hot then the reading become different and so the experiment would be wrong.
Length of wire: I made sure then the wire didn’t slip out of the masking tape, this is because if it did the wire wouldn’t be straight then there is more wire of the current to get to through so change the current reading.
Taking the equipment apart: after every run I took the equipment apart and then re-assembled it. I did this because if I had set the experiment up wrong then I would notice in the next run.
Keeping the voltage the same: I did this to ensure that the volts going in to the wire remained the same, if I didn’t then the current reading would have changed.

Results

Voltage

I put all my results into a table and I calculated the resistance by doing: Resistance =

Current

Run 1 Run2

Run3 Average run

Here are some graphs, which I have drawn up using my results; I have drawn them because I believe that the results become easier to read on a graph than in a table.

Analysing and drawing conclusions

This experiment has shown that the longer the wire the lower the current. So the experiment has proved my prediction. The patterns of the graph for the current readings are as I predicted in my predicted graph. The line starts very high, at 10cm and drops very quickly until it is flat. This shows that the difference in current reading changes very fast to about 30cm. Longer than 30cm shows that the difference in current readings decreases.

Results I collected from these experiments, I conclude that the longer the wire is the lower the current will be. This agrees with the scientific knowledge I researched. The longer the wire is, the more particles there are for the current to force it way past, therefore the current reading goes down.

What the graphs show.

The “How length of wire affects current” graph shows us at 10cm to 30cm the current drops very fast, but lengths longer than 30cm start to flatten out, this is where the current doesn’t change much. The “Temperature” graph shows that the temperature remains quite flat throughout the experiment, this is good as it shows my fair testing worked. The “Resistance” graph shows that the longer the wire the higher the resistance will be. This is because there are more positive ions to get in the way of the current.

Evaluating evidence

I believe that the experiment went very well as I got accurate results and they were all very similar, but any strange results have been circled on the graph. These anomylies could have been for a number of reasons:

Voltage wasn’t quite on two volts.
The temperatures were higher or lower that usual.
Crocodile clips were not on the number as precise as it should be.

I think that the procedure was very good, but if I could change one thing it would be to wrap the wire around the thermometer this would give me more accurate results for my temperature readings. I believe that the evidence I have does support my prediction, but a further two runs would have been helpful.

If I were to continue with this experiment I would use copper wire. I think that the copper wire would offer less resistance because all electrical wires are made from copper, as it is more efficient. I would then continue trying other wires made from different materials to see which is the best and worst at conducting current well. Other ways to extend my experiment are as followed:

Use ammeters and voltmeters to 3 decimal places: this would give me more precise results.
Width: this would give me new results.
Temperature: this would lower the current as the ions are moving more.
Type of metal: different metals have different resistance so the current reading would change. On this experiment I could see which wire offers less resistance and so would be more economical.