The two types of wire that I will be using is Nichrome s.w.g 32 and Constantan s.w.g 32.
Most importantly I will record the length of the wire. The total length of the wire will be 100cm and I am hoping to take 10 recording because it will give me enough readings to draw a graph.
So to get a wide range of results I will use the below readings for the length of wire:
100cm, 90cm, 80cm, 70cm, 60cm, 50cm, 40cm, 30cm, 20cm, 10cm
I will start at 100cm and work backwards.
Another reading I will take is the potential difference (V), I will take each set of 10 readings and repeat them at least once to ensure that they are accurate, then work out the average of the two, I will then calculate the resistance (Ω) from the average potential difference.
When I have obtained these results I will present them in a table with the following format.
Prediction
I predict that as I increase the length of wire, the resistance will increase. I know this because as George Ohm discovered that the Length is directly proportional to resistance.
An electrical current is the flow of electrons through a conductor, in this experiment the conductor is the wire being tested. When the current is flowing through the wire there are electrons moving towards the positive terminal, but there is also atoms from an opposing force travelling the opposite way. When these two forces collide they lose some of their kinetic energy which is given off as heat. This is called resistance. So if I double the length of the wire I am also doubling the amount of electrons, which will result in more collisions and more heat given off, therefore doubling the resistance.
I predict that length is directly proportional to resistance, so as you increase the length, the resistance increases.
On the next page I have produced diagrams to help back up my prediction and to help with the explanation.
Electrons flow from B to A, this is an electrical current. A current is represented by the symbol I.
Resistance=V/I
Below is a diagram of the same type of wire but twice the size.
The number of electrons reaching A has fallen by a half. Therefore the current value is now I/2 (Half it’s original value). So the resistance is now R=V/(I/2)=2V/I, meaning that the resistance is now double its original value.
Method
I set up my circuit as shown earlier. I first tested Nichrome s.w.g 32 which I measured at just over 100cm so that I could attach the crocodile clips to either end. Once the circuit was assembled I turned on the power and set then current to 0.80Amps, which I kept the same throughout the investigation by using a variable resistor. Once the current was at 0.80Amps I recorded the potential difference (Voltage).
Once I had taken down the first set of results, I set up the next set.
First I adjusted the length of the wire by reducing it 10cm, I measured the length on a meter ruler and put a bend in the wire where the measurement was, the reason that I didn’t cut the wire was so that it could be used again in another experiment. Then I attached crocodile clips to the wire so that it was linked in the circuit. Then I turned on the power and adjusted the current to 0.80Amps.
I carried out this process until I had recorded all of my results.
I recorded my results in a table on the next page.
Results
Wire type: Nichrome
Thickness: 32 s.w.g
Current: 0.80 Amps
Wire type: Constantan
Thickness: 32 s.w.g
Current: 0.80 Amps
Analysis
From my results in the table above I have been able to plot two graphs to show the increase in resistance when the length of the wire is increased.
From analysing my graph I have observed that it is nearly a straight line which proves that length is directly proportional to the resistance.
To prove this theory correct I will now investigate into how much resistance is in proportion to the length.
I have chosen five lengths to see whether the increase in resistance is the same for the same amount of length that is continuously increased. I will find the lengths on the graph and then find the resistance that is proportional to that length and present these in the tables below.
Nichrome s.w.g 32
Av. R= 4.8
The results above show me that with every 25cm of Nichrome wire I am adding an average of 4.8 Ω to the resistance. So each 25cm of Nichrome s.w.g 32 wire is a 4.8 Ω fixed resistor.
Constantan s.w.g 32
Av. R= 2.1
The results above show me that with every 25cm of Constantan wire I am adding an average of 2.1 Ω to the resistance. So each 25cm of Constantan s.w.g 32 wire is a 2.1 Ω fixed resistor.
This proves that when I increase a length of wire I am adding resistors in series to the circuit. The diagram below helps explain this.
If I add two resistors then I am doubling the length, therefore the resistance is doubled.
This proves my original prediction correct that resistance is proportional to length. I know this is correct because the tables on the last page showed that when you double a length the resistance also doubles because you have doubled the amount of atoms in the wire. When the resistance of a 25cm Nichrome s.w.g 32 wire is 5.2 Ω and the length is then doubled to 50cm the resistance is nearly doubled to 10 Ω. Even though my results aren’t entirely accurate you can still see that the theory works.
My results support my prediction well and show a good line of best fit in my graphs, but I think that my results could still be more accurate.
This conclusion is only true for the wires that I have tested because I haven’t gained any results from other wires so I cannot state whether I think the results will be the same. But as the metals are Ohmic conductors the theory should work.
Evaluation
As I have straight line graphs the procedure must have been reasonable.
By looking at my tables of results I can’t spot any anomalous results by when I plotted my graphs I noticed that not all of the points were following the line of best fit. But these results were out of pattern by only a few decimals which is why I didn’t spot them in the table or decide to rerecord them because the mistake was so small.
Other than two very small anomalous results in my graphs I think my results are very reliable and accurate that supports my prediction well.
How could I improve my procedure?
Although my procedure and investigation went well I feel that I could of improved it.
One of the mistakes I was making was measuring the length of the wire because I wasn’t doing it accurately as it is difficult to get an accurate reading by eye. It also gives inaccurate measurement when I bend the wire to determine its length. This would have had a slight effect on my results as the wire wouldn’t be at the correct length.
If I was to repeat this experiment I would cut the wire instead of bending it as this gives a more accurate measurement. To make measuring the wire easier I would attach a crocodile clip connected to a circuit at one end of the wire and have an adjustable crocodile clip so that it can slide along the length of the wire until it is at the correct measurement, this would make the process easier and more organised so less errors would be made.
Another problem that I found was that the voltage was not steady and made reading more approximate, which may have given some anomalies in my results. But if I was to repeat the experiment I would use batteries as a power supply as they give a smoother supply. The graphs on the next page show why it is better to use batteries as a power supply.
If I was to improve the accuracy of my results I would look into factors that effect resistance. From my scientific knowledge I know that there are four main factors that effect resistance, they are:
- Length of wire current is flowing through
- Thickness of wire current is flowing through
- Material current is flowing through
- Temperature
So in order to improve the accuracy of my results I must consider controlling all of these variables.
If I was to repeat the investigation I would study the thickness of wires and investigate into whether the thickness of a wire effects the resistance. I Predict that the thicker the wire the lower the resistance. This is because there is more space for electrons to move more freely meaning less collisions with other atoms which means a lower resistance. The thinner the wire the higher the resistance because there is less space for electrons to move about so more collisions with other atoms will occur causing a high resistance. So as the wire width is increased then the resistance decreases.
Another factor that occurred in the experiment was the resistance in the crocodile clips and the wires that connected the circuit. If the resistance in these materials were high then this would have an effect in my results because it would make the resistance in the wire that I am testing higher than it should be. So in order for me to record the true resistance for the wire that I am testing I would have to first discover the combined resistance of the crocodile clips and leads then subtract this resistance from the total resistance in the circuit.
C= A - B
A= Total resistance in the circuit
B= Combined resistance of crocodile clips and leads
C= Resistance of wire being tested
Finding the true resistance of the wire being tested would give me even better results as they would be more accurate which may make my graph lines travel straight through the origin, which would prove that length is directly proportional to resistance.
