Determining a maximum and minimum diameter for the wire
I decided to use the maximum and minimum values of wire that were available. These were 14SWG and 32SWG. I decided to use all of the available thicknesses as it would give me a more accurate set result.
Determining a material to use for the test wire
I decided to use Tin plated Copper wire. This is because it has the greatest amount of different diameters available. Other available wires included Aluminium and Constantine. There was only 1 diameter of aluminium available and 5 diameters of Constantine. Therefore I chose the Tin plated Copper as it had 9 different diameters. The copper ranges in diameter from 14SWG to 35SWG.
Determining how temperature change effects resistance of a Wire
To test this I used a piece of Ni-chrome Wire of 32 SWG. I applied a voltage across it and a current through it.
The results of this test are shown below.
At 2.01 Amps and 6 Volts the wire began to change colour and glow. At 4.42 Amps and 15 Volts the wire melted. I know that for a wire to glow red hot takes around 800˚C. From this experiment it is necessary to keep the current below 1 Amp in my test as this will have a lower effect on the change in temperature and a large change in temperature can affect the resistance of a wire.
The above table shows how an increase in current through a wire increases the resistance of the wire. This is due to the heating effect the current has on the wire. The table above shows that currents greater than 0.6Amps have a significant heating effect such that the resistance of the wire is changed.
Determining a current to use
From the experiment on the effect of heat I have decided to use a current of 0.6 amps. This is because it is the largest current I can use without it heating up the wire and affecting the resistance. I decided to use the largest current before the heating effect changed the resistance as it will give a larger change in the resistance of the test wires which will make it easier to record and will give smaller uncertainties.
Determining a resistor value to use (if any) to protect the circuit.
I decided to use a variable resistor so that it can easily be changed to give the desired output current.
Determining an Ammeter and Voltmeter to use.
I have decided to use 2 digital multimeters’ to measure the Voltage across the test wire and the current through the wire. I have chosen to use these as the uncertainties are lower than any analogue Voltmeters and Ammeters available for me to use.
Determining a power supply to use
I have decided to use a battery pack power supply as the voltages can be easily varied.
A table showing conversions from SWG to cm.
Instructions
- Set up the circuit shown below. Using 2 multimeters to measure the current through the test wire and the voltage across the test wire. Leave a gap in the circuit for the 1m test wire.
- Measure 1m of tin plated copper for every different diameter to be used in the experiment.
- Put the 1m test wire into the circuit using 2 crocodile clips.
- Put a voltage across the test wire and a current through it. Measure both of these and record the results.
- Put the next diameter of test wire into the circuit and repeat the test. Repeat this for every diameter of wire to be used.
Below is the circuit I will use.
Equipment List
1 metre rule
2 digital multimeters
Variable resistor
4mm leads
2 crocodile clips
Battery Pack
Selection of test wires
Results (Test 1)
Results (Test 2)
Average Resistance
Voltage Uncertainties
Maximum Voltage uncertainties is 5%.
Graph of raw results
All graphs require units on the axes
Resistance of wire versus diameter of wire. The trend line on the graph shows some sort of inverse relationship between the Resistance of a piece of wire and its diameter.
By drawing a graph of Resistance versus I can confirm or deny this relationship
Graph of versus resistance
The graph has been plotted with a trend line added.
Units on axes
The trend line on the graph shows that the relationship between versus resistance is similar to that stated earlier. The line doesn’t quite cut the origin but this appears to be due to uncertainties and rounding errors.
Evaluation
The maximum uncertainty for the voltage was 5% and the uncertainty for the length of the wire was ±5cm or 5%. The uncertainty of the current was ±0.01 Amps or 2%. This gives an overall uncertainty in the experiment of 12%. The gradient of the line should be equal to.
None of my results fit exactly on the line of best fit. However 4 of these can be classed as acceptable as the percentage difference between the points and the line of best fit is lower than the maximum uncertainty I worked out earlier to be 12%.
My experiment has several anomalous results. These are the first, second, third, seventh and eighth results taken. These results are a larger percentage away from the line than my maximum uncertainties suggest they should be.
It is possible that because the final result is so far away from the others on the graph that it has caused the line of best fit to be skewed and it may be that with more results within the specific range the line of best fit may be more accurate and therefore cause the anomalous results to be within the percentage uncertainty.
Improvements
- To improve my experiment I could have used more precise voltmeters and ammeters, ammeters and voltmeters with more precision would have decreased the uncertainties for each measurement and therefore given me more accurate results.
- I could have also used a 2metre rule to measure the pieces of wire as this would not involve putting 2 separate rules together and could have decreased the percentage uncertainties in the measurements. Alternatively I could have used a long tape measure to take measurements larger than 2 metres.
- When measuring the thicker wires they were very difficult to get completely straight. To reduce the uncertainties caused by this I could have taped the wire to the rule at different points to help keep it straight.
- I could have used a larger selection of different diameter wires. This would have produced a graph with more results plotted on it, therefore the line of best fit would have been more accurate.
