What Factors Affect the Resistance of a Wire in a Circuit
The four factors which will affect the resistance of a wire are :
- Thickness
- Material
- Length
- Temperature
If the wire were thicker there would be more space for electricity to pass through.
If the material changed it would have a different density so there may be more particles in the way of the electricity current.
If the wire is quite long then it takes a longer amount of time for the electricity to pass through.
If the wire is heated then the less electricity can pass through as the particles begin to vibrate when heated.
The two factors which I have chosen to investigate more thoroughly are THICKNESS and LENGTH.
My Prediction
As the wires thickness increases there will be more space for the electricity to pass through.
The red arrows represent electricity.
So if the cross section (thickness) of the wire doubles then the resistance would half and the flow of the electricity would also double. Using a parallel circuit is exactly the same as altering the thickness of the wire. You can see from my preliminary work that resistors allow more electricity to pass through a circuit.
A good example to demonstrate this is to use a bucket of water. If you made a hole the size of your finger in the bottom of the bucket then obviously water would fall through the hole, however if you then made another hole in the bottom of the bucket considerably more water would run out of the bucket because of the second hole. It’s the same with the wire, the wider the wire is the more electricity can get through.
This can all be explained in the equation:
I = Q or Current = Number of charged particles
T Time
This is because as the cross section (thickness) of the wire increases then so do the number of particles (Q). If Q increases then so must I (the current) meaning that the resistance will be less. The graphs that I will produce from the results should look like this:
So as the cross section increases so do the number of charged particles but the resistance falls.
As the wires length is increased the time taken for the electricity to pass increases.
So, if the length of the wire doubles then the resistance would also double and the flow of electricity would half. Altering the wire is exactly the same as using a series circuit. You can see from my preliminary work that resistors in series circuits allow less current to pass through a circuit.
An easy way to explain this is to use a corridor. If we made 30 people walk down a corridor 50 metres it would take them a certain amount of time, however if we then made the same people walk down a corridor 25metres long at the same speed then it would obviously take them longer. So by making the wire longer it gives the current further to travel so will take longer, just like the people in the corridor.
This can also be explained in the equation:
I = Q or Current = Number of charged particles
T Time
This is because as the length of the wire increases then so does the time taken for the electrical current to pass through the wire. So if time (T) increases the n the current (I) must decrease meaning the resistance will be more. The graphs I will produce from the evidence will hopefully look like this:
So, if the length increases the current will decrease but the resistance will also increase.
Plan
Cross section diagram
single double wire
Method
- Attach a single wire into the circuit, make it 10cm long
- Make a note of the current shown on the ammeter.
- Then increase the length of the wire from 10cm to 20cm and make a note of the current.
- Repeat this extending the wire 10cm each time, stop when you reach 100cm
- Then repeat the entire experiment making the single wire a double wire.
Length Diagram
0 10 20 30 40 50 60 70 80 90 100
Safety
In this experiment normal laboratory rules apply. Also the wire will get hot, be careful not to touch it as it will burn anyone who does.
Fair Test
To make it a fair test I will repeat the readings. I will also, make sure I keep the same battery pack so that the resistance originally caused by the pack will be the same. I will make sure I extend the length in even amounts of 10cm each time. I’ll make sure the voltage stays the same for both experiments. I’ll be quick with the readings so that temperature doesn’t affect the readings. I’ll also have only one variable at a time so that there is less chance of human error
Results
Single Wire
Length Current Voltage Resistance
10 1.47 2.5 1.7
20 1.14 2.5 2.2
30 0.92 2.5 2.7
40 0.80 2.5 3.1
50 0.70 2.5 3.6
60 0.62 2.5 4.0
70 0.56 2.5 4.5
80 0.49 2.5 5.1
90 0.45 2.5 5.6
100 0.42 2.5 5.8
Length Current Voltage Resistance
10 1.63 1.8 1.1
20 1.39 1.8 1.3
30 1.22 1.8 1.5
40 1.09 1.8 1.7
50 0.99 1.8 1.8
60 0.90 1.8 2.0
70 0.84 1.8 2.1
80 0.78 1.8 2.3
90 0.73 1.8 2.5
100 0.69 1.8 2.6
Conclusion
My evidence for the increase in thickness experiment shows that when the thickness increases the resistance decreases and that when the thickness increases the current also increases. On the resistance/length graph as the thickness of the wire doubles the line on the graph becomes less steep. On the current/length graph as the thickness increases the line gets steeper meaning the current decreases at a faster rate. On the resistance/ length graph the resistance increases in very regular steps, enough to draw an extremely accurate line of best fit for each thickness. On the current/length graph there is a very clear negative curve presented from each thickness showing us that when the length is a small value the change in current is very big compared to when the length is a large value.
The formula I = Q/t supports my results as, when the space for the particles to get through increases, the time taken for them to get through decreases. Hence, as the formula shows, if the value for time taken is less, then the value for the current will be greater.
My conclusion supports my prediction as I said that as the area of the cross-section increases the resistance would decrease. However, in my conclusion I cannot say that material used instead of wire will produce the same results and I don’t know whether, should the wire were to be at a different temperature, my results would be the same. My graph does tell me that the battery also has an inside resistance as, when my length of wire is 0 cms, there is still a resistance in the circuit.
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My evidence for the increase in length experiment shows that when the length increases the resistance also increases and that when the length increases the current decreases. On the resistance/length graph as the length increases the line on the graph becomes steep because the resistance is increasing. On the current/length graph, as the length increases the line curves downwards because the current is steadily decreasing. As shown by the blue pen on my resistance/length graph, as the length doubles so does the resistance. Any resistance up to 1 is just general resistance produced by the circuit; however, after this the resistance is increased by the length getting longer. If you look at the line when the length is 60 cms you can see that with a double thickness wire the resistance is 2 but when it’s a single wire at 60 cm the resistance is 4. This proves that the cross-section halves the resistance doubles.
This conclusion supports my prediction because in my prediction I did say that as the length increases so does the resistance. However, I was wrong in saying that as the length doubles so would the resistance. If you look at the single wire on the length/resistance graph, when the length is at 50 cm the resistance is 3.6. For my theory to be correct, the resistance at 100 cm would have to be 7.2 but it is not – it’s 5.8 which is a lot less, proving that my theory was wrong.
Evaluation
The experiment we used worked well without any serious problems. However, two things that I did notice was that current fluctuated and the wire grew dangerously hot. I don’t think that there were any anomalies – my results all seemed reliable. I think this not only because there was nothing very obviously wrong in my results table but also that all the points on my graph either sat directly on the lines or were extremely close to the line of best fit.
As I was doing the practical experiment I notices that the temperature of the length of wire in the experiment grew so that, if touched, it would burn someone badly. To avoid this next time I would be faster and not leave the wire attached to the electric circuit whilst other things are adjusted with the apparatus. I also think that next time I will use a power pack instead of singly battery cells. Hopefully, by doing this, I would reduce the amount of resistance already in the circuit even before the experiment is started.
I think that the evidence is very reliable and is completely sufficient to support my conclusion. If I was to repeat this experiment I would try to find more evidence to support my conclusion. I would change the material of the wire to see if resistance changes in different materials or whether it is just in length of cross-section that resistance changes. Also, given more time, I would keep increasing the cross-section of the wire by twisting three, and then four, single wires together to see if the trend of resistance continues – which I would expect. Also, as a precaution, I would use longer lengths of wire, not continue extending the length only by 10 cms each time but more like 15-20 cm. This would prevent the wire getting so hot.