In a thick wire the resistance would be less because there is less chance of a collision.
Temperature changes affect the resistance of materials in different ways. In some materials an increase in temperature causes an increase in resistance, whereas in others, an increase in temperature causes a decrease in resistance.
The type of material the wire is made of also affects the resistance. Metals are natural conductors but some metals conduct more easily than others (copper conducts better than iron and nichrome).
Apparatus that I’m going to use.
Crocodile clips – to connect the parts to create a circuit.
An ammeter – to measure the current in a circuit.
A voltmeter – used to measure the voltage.
A power pack – to supply power to the circuit.
A ruler with the length of wire to be tested attached to it – to complete the circuit and determine the length of wire at 10 points along the ruler, starting at 100cm then at 10cm intervals down to a 10cm length.
A variable resistor – used to change the resistance in a circuit, which I won’t need to do.
This apparatus is shown in Figure 1 below.
Figure 1- Circuit diagram
Preliminary work
Before I did the actual experiment to examine the resistance in a wire I decided to do some preliminary work to determine the most suitable wire to use.
I mentioned earlier that the material of the wire would affect the resistance. I performed some tests to see if this was the case.
I calculated the resistance by using Ohms law: -
R = V / I
The results I obtained during the preliminary work are shown in Figure 2 below.
Figure 2: Table showing the ammeter, voltmeter and resistance reading for each wire.
All figures are rounded to 1 decimal place.
After obtaining these results I decided to use a nichrome wire in the actual experiment. Although it has the highest resistance it’s the only wire that didn’t go below 1 ohm at 20 cm. and therefore should be the easiest to obtain measurable results in the shorter lengths of wire.
Hypothesis
Using Ohm’s law I predicted that as the voltage decreases there will be less resistance. I predicted this because if the current had stayed fixed, then reducing the voltage would automatically reduce the resistance in the Ohm’s Law formula.
If there is a high voltage there will be a high resistance. With a low voltage there will be a low resistance.
I also predicted that the resistance would decrease depending on the length of the wire (the longer the wire the higher the resistance).
Method
Before performing the tests I wrote down what I should keep the same in order to make it fair, which were: the type and diameter of the wire (by using a single length of nichrome wire); the length of the wire (by accurate measuring and moving the crocodile clips); and the temperature (by waiting in between taking readings).
I set up the experiment as shown in the circuit diagram (Figure 1) using a 100cm length of nichrome wire (which ensured the same wire diameter and wire type were used for all readings). I then turned on the power and took a reading with a 100cm wire length. After noting the reading I moved the clips by 10cm to make the wire length 90cm. By using a ruler I was able to accurately measure the wire length and ensure the clips were placed in the correct position each time I took a reading.
I then took another reading and repeated this process taking readings at 10cm intervals until I reached a wire length of 10cm.
I chose a maximum length of 100 cm because anything longer would have caused the wire to have a higher resistance which in turn would have caused less current to flow through it.
I made sure that the temperature remained constant by turning off the power pack and leaving a 2-3 minute gap between each reading.
After taking all of the readings I repeated the experiment a further two times and wrote down the readings.
I then calculated the resistance for each reading.
After noting all the calculated resistances I calculated an average value giving me an average resistance for each length of the wire.
Using the average I plotted a graph showing the resistance change due to the length of the wire.
Results
Figure 3 – Table showing the ammeter, voltmeter and resistance of the wire I tested.
Graph showing the average resistance in each length of wire.
Evaluation
On the graph I have drawn a line of best fit in order to estimate the relationship between the length of wire and the average resistance. As you can see, the points do follow the line fairly closely. The points for the shorter lengths are furthest away from the line of best fit. This could suggest that they are more prone to experimental error. On my graph, the points are quite close, but in reality they may be even closer.
At lengths 60 and 70, the points are almost identical. This may be an anomaly, perhaps caused by the wire becoming too hot.
I am quite pleased with my results. They are quite accurate. I can tell this by the readings I obtained (which were very similar) when I repeated the experiment.
They weren’t exactly the same but this could have been for a variety of different reasons. For example, as I’ve already said, the wire may have become too hot which would affect the resistance as the current flows faster with heat and therefore the resistance would have increased.
If I did the experiment again I would leave the power pack turned off for longer in between taking each reading so I could be absolutely sure that heat did not affect the results.
I would also make the wire longer to see if there was any noticeable difference in a wire longer than 100cm.
If this test was repeated by someone else they would obtain results similar to mine. They wouldn’t be exactly the same, however, as it depends how they are reading the scale and whether the equipment is set up correctly etc.
To further test my predictions I would do the experiment on other wires and not just on nichrome. I would use the copper, iron, steel and/or brass wires.
If someone did all of this, their results may lie even closer to the line of best fit on a graph.
Conclusion
From my results you can see that my hypothesis was correct. I found out that as you increased the length of wire, the resistance also increased.
