Results
Conclusion
From these results, I have decided that 1 volt is the best idea. This is because it will still show many readings, but will not overheat the wire.
Investigation 2
Aim
To choose a suitable wire for the investigation. The wire must have a large range of results and must not overheat at short or long lengths.
Method
For this experiment I will need to test many different wires. I will set up the apparatus shown in the diagram and take the reading of current when the voltage is 1.0. The wire will be set at 90cm and then at 10cm.
To make the voltage exactly 1.0 I will use the variable resistor to make changes. I can see the voltage on the digital voltmeter.
Diagram:
Results
Conclusion
As you can see from my results, I did not use copper in this experiment. This is because even below 1 volt, it heated up. Therefore I can not choose this as my main investigation wire. I have decided to use Nicrome 0.31. This is because there is a large range of results, but the wire did not heat up at short or long lengths. This makes the investigation safer. If we had chosen for example copper, there would be a great hazard due to the hot wire. This would also have been true of Constantan 0.45.
Main InvestigationAim
To find out how current changes when the length of the wire is changed.
Method
For this experiment I will need to test many different lengths. I will set up the apparatus shown in the diagram and take the reading of current when the voltage is 1.0. The wire will be set at 10cm and then increased by 10cm for each reading. Every time I vary the length I will adjust the variable resistor to make the voltage exactly 1.0. For fair testing, I will try each length (10cm, 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm & 100cm) twice, with different wires of the same type.
To vary the length of wire I will use crocodile clips attaching them to a piece of wire on a metre rule.
Diagram:
Prediction
I predict that if I increase the length of the wire, this will increase the resistance. Therefore the current will decrease. I think that this will happen as I know that my wire is made of metal, and all metal contain atoms. The atoms are made up of protons, neutrons, and electrons. The electrons are free moving, and therefore if we apply a voltage, the electrons will ‘drift’ from the negative to the positive.
I predict that if the length is doubled, the resistance will double. Resistance is caused when electrons flowing towards the positive terminal have to ‘jump’ atoms. The electrons will have double the distance to travel, double the amount of ‘jumps’ so the resistance will double. Twice the energy will be needed.
If I was to draw a graph, I predict that it will be a straight line through the origin. Thus showing that the resistance is directly proportional to the current.
Results
Analysis
From my resistance graph you can see that the resistance is directly proportional to the length of wire. When the length of wire is doubled, the resistance is also doubled. For example, when the length of wire was 50cm the resistance was 8 Ω and when the length of wire was 100cm the resistance was 16 Ω. And at 30cm the resistance was 4.8Ω doubling to 9.6 Ω at 60cm. When the resistance increases, this decreases the current as the current needs more energy to travel though the resistance.
This is because of the scientific idea, stated in the prediction that if you double length, you double the number of atoms in it, so doubling the number of electron ‘jumps’, which causes resistance: The results support my prediction well, the results turned out the way I had expected. I had predicted a straight line through the origin, which means R is directly proportional to L.
The graph of current and length of wire is an inversely proportional curve. This is because L (length of wire) is directly proportional 1/I, this means when L doubles, I halves. For example when the Length of wire is 20cm the current is 0.28. When the length doubles to 40cm, the current halves to 0.16A. When L doubles again (to 80cm), I halves again to 0.08A. This is because, as stated earlier: We see that if the length of the wire doubles, so does the number of jumps for the current to pass over. Therefore the energy is twice as spread out, so resistance might halve, i.e. Resistance is directly proportional 1/Area.
Evaluation
At 40cm and 50cm the current was recorded to be too high. The points on the current graph lay slightly above the best-fit line. This could be because the equipment I used may have been as accurate and reliable as I might have hoped for.
There are several improvements I could have made to this investigation. Firstly I could have used fresh wire. The wire I used had been used before and had many notches in it. This would change the length of wire I would have been measuring. The wire was also burned in places, perhaps causing a less secure connection between the wire and the crocodile clips. Also to improve the investigation I should use more accurate voltmeters, ammeters and variable resisters.
