Type of material:
Different materials have different resistances because the materials’ atomic structures are different so some metals have low resistances and some have high resistances. Therefore it is important to keep the material the same throughout the experiment unless a different material is used to check if the conclusion or theory works for all materials. If different materials are used throughout the investigation, it will affect the results. For example if sometimes copper is used and sometimes nichrome is used, the results where copper is used will be of a low resistance because of the material and not because of the diameter of the wire. Throughout the experiment Constantan will be used. The type of material will affect the amount of free electrons that are able to flow through the wire.
Diameter of the wire:
This is to be the same because the wider the diameter means more free electrons can flow easily and aren’t so compact together and when smaller it is the same amount but in a smaller area affecting the resistance.
All these factors must be kept constant to make the investigation fair. The same apparatus must be used throughout the investigation. It is also important to take three repeat readings and find the mean so if one result is very inaccurate, the others will average it out.
Method
Apparatus:
Power Supply/Power pack, to regulate the mains power supply and bring 240v standard mains down to a safe amount.
Ammeter, to measure the current of the circuit in amperes.
Voltmeter, to measure the voltage of the circuit in volts.
Wire Constantan, to use to test the resistance in the circuit and conduct electricity.
Meter Rule, to accurately measure the length of the wire constantan.
Crocodile Clips, to provide safe contact between the components and the wire
Wire clippers, to safely cut the wire when reducing it’s length. Wire-board, to safely and accurately hold the wire.
I set the equipment up in the above way. I measured the length of the wire from one crocodile clip to the other showing the distance the power is passing and to measure the voltage, current and resistance we used the power pack as well at 2 volts.
Safety
Handle the power supply carefully.
Be careful when touching the wire, as it may be hot.
Start on the lowest current, so the wire then will not melt or burn instantly.
Be careful when the wire is connected, as it will get hot.
Be careful when cutting the wire.
Make sure the main to the power supply is switched off when removing the wire from the circuit to be measured. Keep my work area clean and tidy to avoid confusion.
Predictions:
I think the longer the wire transporting current the higher shall be the resistance because the longer the wire the longer it takes the electrons to go through and also find it difficult as more collisions occur during the flow. So shorter the wire easier it shall flow and quicker as less to travel through. Below my graph shows what my prediction is viewed to be:
I plan to take three readings per length of wire because it will make it more accurate and I can solve any misunderstanding or errors in my results.
The range of my results is 10cm wire length to a 100cm length of the constantan wire.
Analysing Evidence and Drawing Conclusions.
From doing this investigation I have found out that the longer the wire the higher the resistance.
From the graph, I can see that the resistance of the wire is proportional to the length of the wire. I know this because the Line of Best Fit is a straight line that passes near enough in the region on the origin, showing that if the length of the wire is increased then the resistance of the wire will also increase. This means that resistance is directly proportional to length. For example, if the length is 40cm, and resistance is 2, then if length is doubled to 80cm, resistance also doubles to 4.
The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions, which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase. The results satisfy Ohms Law also as doubling incurs both places i.e. double the voltage doubles the resistance. All this proves that my prediction was spot on “higher the resistance the longer the wire”.
On my result table it also shows that the longer the wire the higher the voltage and lower the current and the resistance goes higher.
The results from the graph give a clear indication of how the resistance compares to the wire length. There is a very strong positive correlation.
The theory behind this is explained in the prediction. In any given metal wire, there are a number of atoms and free moving electrons. Electricity is the movement of these electrons through the wire. Resistance is caused when the free electrons moving through the wire collide with the atoms making their path through the wire more difficult. This means that if there are more atoms in the way to collide with the free electrons the resistance is increased. In a length of wire there will be a number of atoms, and in a wire twice the length, there will be twice the number of atoms. In turn this will lead to there being double the number of collisions between the electrons and the atoms increasing the resistance by 2. This explains why the results were directly proportional. For example a wire that was 10 cm long may have 500 atoms blocking the electrons. Therefore in a wire 20 cm long, there would be 1000 atoms meaning that the resistance had doubled. The line of best fit clearly shows that the results followed the expected pattern very well. The points are very close if not touching the line. This shows how the results were directly proportional through out, as the gradient remained the same.
Below you can see a small picture of my theory:
