Plan
There are many factors, which could affect the resistance of a wire; they are the length of the wire, the temperature, the material the wire is made of and the thickness of the wire. I will be investigating the length of wire.
Apparatus
- Battery
- Wires
- Ammeter
- Crocodile clips (2)
- Voltmeter
- Ruler
Method
Set up all the equipment as shown in the diagram above, and then using a ruler measure 50cm of wire (in our preliminary work we got a got a good idea of range of results we were likely to get, we shortened the wire by 10 each time but then decided 5 would be better). Then connect this to the circuit and then begin to take readings from the voltmeter and ammeter. Then the experiment needs to be repeated another 2 times with the same length of wire to ensure an accurate reading is taken. I will change the length of wire to 45cm and do as I did at 50cm. I will continue to do this until I get down to 5cm (go down 5 every time).
To work out the resistance use this equation: -
Resistance =
Fair Test
To ensure that this is a fair test I will use the same battery, voltmeter and ammeter through the experiment. It is also important that I take the battery out between each reading as if I left it in the wire will get hot and temperature would be another variable and so this would make my test unfair. I must also make sure that the wire used is the same thickness each time and that it is made out of the same material, as these are also variables.
Safety
To keep safe in this experiment I must ensure to take care when handling the wire once it has been used as it will be hot and may be melted. I must also make sure my hands are dry as if they are wet it is dangerous.
Results
All results fit the general pattern; there are no anomalous results.
Analysis of graph (conclusion)
The graph shows positive correlation. This tells us that as the length of the wire increases so does the resistance. There are no results that seem out of place. My results support my original prediction. My graph shows that as length increases so does resistance this is because in a longer piece of wire, there are more particles for electrons to push past, this makes it harder for electricity to flow so resistance increases.
Here is a diagram showing this: -
Evaluation
I think that my experiment went well because it was safe as no one was injured. I think my results are accurate as I repeated each experiment twice and they look right. I did not find the method hard, but it was not easy to measure the length of wire, as I had to straighten the wire every time, I may have measured the wire off a few millimetres, which could have affected my results. The voltage also went up each time, which it should not have done. Another problem I encountered was that the value on the ammeter and voltmeter sometimes changed as I was writing down the value it said, this could affect the experiment as a lower/higher result than it was and this would also affect the resistance. Although the battery was supposed to be disconnected after each reading it may not have been so the experiment might have had a heat build up, leading to more resistance on the next length of wire. If I were to do this experiment again I would use a variable resistor to keep the voltage the same.