My prediction is that the longer the wire, the bigger the resistance as this is what has happened in my preliminary experiment.
Planning.
Circuit Diagram:
Apparatus:
Power pack, DC supply
Constantan wire, 28swg, 1.5m
2 crocodile clips
1 metre rule
1 Voltmeter – the highest voltage this will go to is 5.76 volts
1 Ammeter – set at 0.8 amps
Method:
- I am going to set up my circuit from my circuit diagram.
- I am going to use a metre rule to measure my wire to the length that I want it at first.
- I am going to put it into the circuit with the crocodile clips positioned at the end with just the tips holding the wire.
- I am then going to turn on the DC supply with the settings at 0.0A.
- I will then turn the settings up until it is 0.8A.
- I am going to record the voltage and the current at 10cm.
- I am then going to turn everything off and change the length of the wire to the next reading I want.
- I am going to repeat each reading twice at different parts of the wire.
- I am going to get all of my readings and then work out the resistance of them all. I will do this using the formula resistance = voltage / current.
Theory
Current - current is the rate of flow of charge around a circuit.
Charge - charge is measured in coulombs.
1amp is the current flowing when a charge of 1 coulomb flows for a time of 1 second.
The property of a substance in virtue of which the passage of an electric current through it is accompanied with a flow of energy, - an electric resistor.
Length- Components offer resistance to the current. For a particular voltage the length of wire will determine the resistance. Diagram A shows that it will take twice the amount of time for the current to pass through the wire when it is twice the length as shown in Diagram B, than in Diagram A. This is because it has to pass through twice the amount of molecules. The resistance will be directly proportional to the length. When you double the length you double the resistance and when you triple the length you triple the resistance
Thickness- Diagram A is half the thickness of Diagram B yet it still has the same amount of particles. The current therefore will take twice the amount of time to pass through Diagram A than Diagram B, as Diagram A is twice the thickness of Diagram B. The resistance is directly proportional to the thickness. In my experiment I am going to have to keep the same thickness all the way through the experiment otherwise I will not obtain accurate results.
Type- Different types of wires have different resistances due to each wire having a different amount and type of particles. For example if I decided to use the wire in Diagram A for half the experiment when testing the length of the wire and then decided to use the wire in Diagram B for the rest of the experiment the results would not be accurate. Also, they are affected by temperature differently. I will keep the type of wire I am using the same all through my experiment.
Temperature- increasing the temperature increases the energy of the particles inside a wire making them move around more. The more the particles move around the harder it will be for the current to get through. In Diagram A there is little or no heat being inflicted on the wire so the particles inside it are still meaning that the current finds it easy to find a quick path through, whereas in Diagram B the particles are heated and are therefore moving around making it harder for the current to find a path through. It is therefore important to keep the temperature constant throughout my experiment, as this will affect the results.
Results.
Resistance
Analysis.
From the graph there is one very clear trend, which is, as the length of the wire increases so does the resistance of it. Another, more significant thing is that it the increase is constant. This is indicating by the fact that the line drawn is a straight and goes straight through the origin. I think that from my results I can safely say that my prediction was right. The resistance did change in proportion to the length. This is because as the length of the wire increased the electrons that made up the current had to travel through more of the fixed particles in the wire causing more collisions and therefore a higher resistance.
Evaluation.
I feel that overall my results were quite accurate. This is can be seen when we look at the graph, which shows a straight line with all of the points apart from one being very close to or on that line. The one point that was not that close to the line was a slight anomaly, but it was only slight and did not affect the final gradient of the graph. The reason for this could have been due to a number of different factors.
Firstly the temperature of the wire might not of necessarily stayed the same all the way through the experiment as it may of heated a little towards the end and the material of wire may not be as pure as it should have been. The main reason for this was probably due to the equipment that we used being inaccurate. This did not stop us from seeing the trend, though, because the equipment would have been out by a constant amount each time therefore there was a constant error. So the trends that were predicted in the plan still were shown.
Most errors in our experiment were encountered in the measuring of the wire. This is because it simply was not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Also I do not feel that the crocodile clips were always fixed securely to the wire with a good connection. This also meant that they were easy to move about on the wire changing the length of it. Errors rarely occurred in the setting of the current and the reading of the voltage. It was just in the preparation area that they did occur. Another example of this is the wire was never totally straight when we started the experiment, which may also, as said earlier on, affect the resistance of it.
I do not think that doing any more results in our experiment would have made it any more accurate. I feel that the only way to make it more accurate would be to use a different method – perhaps were we had a bar that did not bend in place of the wire. Or we could hang the wire from a stand with a weight on the end of it forcing it to straighten and then clip the crocodile clips onto the wire while it is hanging making the results better.