Year 11 Physics Investigation- What factors affect the resistance of a wire?

Introduction

We are trying to find out if the thickness of a wire affects the resistance of a wire and also how it will do that.

One reason I chose this investigation was because human reaction time is eliminated by not using the parachute method (the parachute experiment is to find out the factors affecting the rate of decent of a parachute), because you have to measure the timings on it by the eye and hand pressing the stop button and there could be some inaccuracies in this. In the test I am doing there is no space for human error because all the measuring is done by equipment and machines so all I have to do is make sure I use them properly and read them with accuracy. The wire resistance experiment is more precise because the equipment I will use to measure all sorts of different factors in the experiment is more precise than in the parachute experiment mainly because everything is still and not moving in the resistance experiment.

We have chosen to do the thickness of the wire because it is easy to control and keep accurate because of the micrometer, which is very precise. In the parachute investigation I would have to measure the distances with a ruler and the micrometers precision is 0.01mm which is a very high precision whereas the ruler has a lower precision of 1mm.

We could have used the material as a variable but when we get a graph of results it will be a bar chart and you can’t get a numerical correlation because one side of the chart is not numbers and seen as we are trying to get a numerical correlation it would be pointless to use material as our input variable.

The temperature is another variable we could have used but it is very hard to control the temperature and we didn’t really know how we could do it so we decided not to use this as our input variable either. We had the choice between length and thickness as our variable randomly because they were both very good to use as input variables.

Diagram:

Apparatus list:

Equipment Reasons why I chose it
Ammeter 0.05 amps precision to measure the amps in the experiment and it is easy to read and fast at measuring.
Voltmeter Precision of 0.2 volts when measuring the voltage, very easy to read and again fast at measuring.
Micrometer 0.01 millimetres precision when measuring the thickness of the wire, which is our input variable so it needs to be very accurate. The alternative to using this would be the ruler and we are not using that because it is a lot less accurate and precise.
Cell The reason we are using this is because it will supply the circuit with enough power to run properly with ease and no hassle whatsoever.
Connecting leads and crocodile clips These allow there to be something to measure. Allows electricity to flow smoothly around the circuit.
Method

Set up the diagram as shown on the first page. Get your 5 wires and measure their thickness using a micrometer. Replace the place in the diagram where the resistor would be found with each of the wires and measure the results on the ammeter and the voltmeter and put the results into a table. Divide the voltage value by the current value to give the resistance of the wire, and add it to the table. Fill in the average resistance column by finding the mean value of resistance for each thickness of wire. The input variable I will be changing is the thickness of the wire. I will measure this using a micrometer. It is important to use a range of at least 5 values for the thickness of wire so that a clear trend can be identified from the results. The outcome variable will be the resistance of the wire, but it cannot be measured directly. To find the resistance of the wire, the voltage reading must be divided by the current reading for each thickness because R=V/I. There are a number of other variables i must control to ensure a fair test. I will talk about these one at a time.

Temperature

Getting all the results in the same lesson ensures that the temperature is reasonably constant and will not affect the reliability of the results. If results were to be gathered on different days, the potential change in temperature would affect the outcome and it would therefore not be a fair test because the investigation is about how thickness of wire affects resistance. High temperature means higher resistance because the atoms vibrate, which means charges in the circuit are unable to flow through as easily than when the electrons are not vibrating.
Material

The wires that are tested will be made out of the same material for every test. Some materials may be more resistant than others it would not be a fair test if we used different materials for each test.

Length

The pieces of constantan wire will be the same length for every test. The wires will already be measured equally for us but I will check that their lengths are equal with a ruler before starting the test. If the wires were different lengths each time, we wouldn’t be able to tell whether the thickness or length of the wire was affecting the resistance because they would both be being changed.

Fair testing

A fair test is important because if there were to be more than one input variable, there would be no way of knowing which input variable was causing the output variable (resistance) to change. Also, having multiple input variables would cause the results to be inaccurate because there would be so many things changing each time it would cause the resistance of the wire to fluctuate. Each thickness of constantan wire will be tested twice, and the 10% rule will be used to make sure the two results are reliable. If the two results are not within 10% of each other, one of them will be repeated until they are.
Safety Precautions

During the experiment, nobody is to touch the wires because it may get hot and burn someone. No drinks or other liquids are to be placed near the circuit during the investigation to prevent serious electrical hazards. Caution should be exercised when handling the wires as the ends are quite sharp and could damage someone’s eyes – it may be sensible to wear safety glasses as an extra precaution.

Preliminary Tests

Wire Thickness (mm) Voltage (V) Current (A) Resistance(Ω)
1 0.21 1.4 0.1 14
3 0.29 1.3 0.2 6.5
5 0.46 1.2 0.4 3

My preliminary tests enable me to see if my technique is okay. Firstly it was too see if my variable was okay; whether or not it was too small to be able to notice the changes in the results made by the equipment I have and the precision they have. Or the results could be too high to measure on the equipment available to us. If this was the case then we would have to alter the input variable but seen as there is a noticeable yet measurable change in our results then there is no need too. As the thickness increases the resistance decreases and this is clear to see so I will have a trend to look at in the proper experiment. There is also a big difference between all the resistance results so there will be plenty of room to notice change in the results I will collect.

All our equipment worked well but there are some improvements that we could make. One is the battery. We could use a power pack instead because the battery could be not working properly or dead and you might not realise and using a power pack will make sure you know that there is a constant supply of current and my results will therefore be more accurate.

I will use a multimeter instead of a voltmeter because the precision of the multimeter is better than the voltmeter, with the voltmeters being 0.2 volts and the multimeter being 0.01 volts so using the multimeter will make my results more precise and accurate.
Results

Thickness (mm) Voltage (v) Current (A) Resistance (Ω)
0.22 1.52 0.13 11.7
0.26 1.52 0.18 8.4
0.32 1.52 0.24 6.3
0.37 1.51 0.35 4.3
0.47 1.49 0.52 2.9

Thickness (mm) Voltage (v) Current (A) Resistance (Ω)
0.22 1.53 0.13 11.8
0.26 1.52 0.18 8.4
0.32 1.52 0.24 6.3
0.37 1.51 0.35 4.3
0.47 1.50 0.51 2.9

Thickness (mm) Resistance Average (Ω)
0.22 11.75
0.26 8.40
0.32 6.30
0.37 4.30
0.47 2.90

Conclusion

I have learned from my results that when the thickness of a wire increases the resistance decreases. When the thickness is 0.25mm the resistance is 9.4Ω and when the thickness is 0.5mm the resistance is 2.6 Ω. When the thickness doubles the resistance divides by 3.6 which is what it is in my results. An electric current flows when electrons move through a conductor. The moving electrons can collide with the atoms of the conductor. This makes it more difficult for the current to flow, and causes resistance. So the thicker the wire the more space for the electrons to pass through the wire without obstruction, and this shown by the drop of resistance as the thickness increases. The smaller thickness of the wire, the more obstructions the electrons will face and therefore the resistance is higher. This is shown in my results so they must be accurate and reliable.

Evaluation

My results were very reliable. I know this because all my results were incredibly close to each other or the same as each other in the repeats. There were no outliers and I didn’t have to use the 10% rule once. I also think my data is very accurate because all my results fit very well onto a line of best fit and my results are not very scattered which also means that they are accurate. I think my method was pretty good and there wasn’t much I could improve on because I made sure I kept my other variables constant and controlled everything in the experiment very well. One thing I would change in the method however is that I would take another 2 repeats of each thickness too make sure my results were more reliable and accurate even though they already are in my opinion. I would also change one thing to do with my equipment in the experiment and that is putting a multimeter where the voltmeter was because a multimeters precision is 0.01 V and a voltmeters is 0.2V so the multimeter is more precise and will give more precise readings meaning my results are more accurate. I followed my method exactly and my technique was very good. For example I made sure I controlled all the variables and made my experiment a fair test. This shows in how precise and accurate my results were. I am very confident in my conclusion that when the thickness of a wire increases the resistance decreases and vice versa. This means that thickness does affect resistance. I am very confident in this because my results show a clear correlation because they accurate, precise and reliable. I am also confident in my conclusion because my technique was very good and the experiment went very well without and problems.