Electrons must squeeze through the gaps in the atoms and this is done easier in the shorter piece of wire than the longer one because there are less atoms, which shows that resistance is greater in the longer piece of wire, shown above. This is shown in the diagram above.
Prediction.
I think that the longer piece of wire is the resistance will be larger. This is because longer pieces of wire contain more non – moving atoms so the electrons cannot squeeze through the atoms.
Apparatus.
1m of resistance wire, crocodile clips, power pack, ammeter, voltmeter, sellotape, metre ruler.
Method.
- Collect the apparatus shown above. Plug in the power pack and set it to a suitable voltage – this will ensure the wire doesn’t overheat.
- Set the crocodile clips to 10 cm on the ruler, make sure there is sellotape on the ruler to keep the wire stuck down.
- Measure the voltage and current, record the results and turn off the power pack so the wire doesn’t overheat.
- Move the crocodile clips up another 10 cm and record your results. Repeat this at least 5 times.
- Repeat all of the experiment, and find the average of your 2 sets of results.
Diagram.
In my experiment I will keep the same type of wire, it will be the same diameter and metal each time, I will also use the same voltage, current and temperature each time to ensure it is a fair test.
I will change the length of wire each time to see how resistance varies. I will be measuring the current and voltage in the experiment and using these to calculate the resistance. To make sure the experiment is a safe one I will be careful when touching the wire as it may be hot, I will also check the power pack and wires to make sure they aren’t faulty.
Results.
I chose these readings because it allows me to see how the resistance steadily increases. I decided to go right up to 100 cm in order to use the full length of the wire.
At the beginning of the experiment we chose to have the power pack on 10 Volts but the wire began to burn so we then turned it down to 6 Volts.
Conclusion.
My results show me that as the length increases so does the resistance, this is what I predicted in the beginning.
From my graph I can see that there are patterns in my results, for example between 20 and 40 cm, the resistance doubles. I can also see that as the length increases the resistance increases steadily because they are in direct proportion to one another. This can be shown as R ∞L when R is resistance and L is length.
I have drawn dotted lines up to my curved line on the graph and used the line of best fit to find the results I should have according to the curve. I then put these into a table in order to compare them with my actual results. This showed me that most of my points were correct.
My conclusion is that as the length increases, the resistance increases. This can be related to my background knowledge and prediction I made at the beginning.
Evaluation.
I think my experiment was quite a good one because I made sure it was a fair test, it was carried out safely and I kept the same variable and constants throughout the experiment.
Most of my results were accurate and fitted my line of best fit; one point, which was quite a way out, was my reading for 100 cm. There are many reasons why this point could have been out, for example human error. If the ammeter or voltmeter had not been read correctly or the power pack had been altered, this would account for a slight error.
I could make my experiment better by taking more results down to ensure it was accurate. I could use a different diameter of wire or a different type. To make the investigation better I could do some preliminary work to give me some background information, this would improve my investigation.
My experiment was good enough to support my conclusion because I made the experiment as fair as possible, and didn’t make many errors. It also agrees with my prediction I made in the beginning.
To extent the investigation further, I could use different lengths of wire; I could also use a different diameter or type of wire. I would use a good conductor of electricity for the wire, gold would be a good metal to use but it isn’t practical as it is expensive. This could improve my experiment.
