For my experiment I have decided that I will see whether the length of wire affects the resistance in a wire and I have also decided to see whether the thickness of the wire will also affect the resistance in a wire.
Prediction
I predict that there will be higher resistance in wires that are longer in length because the path the electrons have to go through is longer. I also believe that as the length doubles the resistance will also double. I also believe that the thicker the wire is the less resistance will be present, this is because the thicker the wire the less the flow of the electrons is impeded.
Preliminary
To determine which type of wire to use we set up a preliminary experiment. The first was to determine what type of wire to use and the second was to determine at what intervals we would use to take results. For example every 3cm or every 5 cm.
In order to do this preliminary experiment we will need.
- 1 x Power Pack (to give varied voltage)
- 1 x Voltmeter
- 1 x Ammeter
- 5 x wires (with crocodile clips)
- varied wires
The apparatus will be set up as shown below.
The varied wires that we will use are silver, constantan, copper and nichrome.
Results
From doing the preliminary experiment we have determined that we should take readings from every 5cm. We have decided this because of the time scale that we are restricted to. The table below shows how long it took to take a reading of a wire of 100cm; at different intervals.
This table shows that it is less time consuming and therefore it will enable us to get a better set of results.
The second preliminary experiment was to determine what type of wire we should use. The three elements that I was looking at were availability, cost and safety.
Nichrome: The nichrome wire was easily accessible and was not expensive. The only problem with the nichrome was that if I went to a low length it heated up quickly which created a safety issue. It is for this reason I will not use the Nichrome wire.
Silver: The silver was not accessible. We were unable to find 100cm of silver wire and it is very expensive. For these reason we will not be using silver wire.
Copper: copper wire is the cheapest wire and is also the safest wire. However many other pupils are using copper wire and the availability will not be sufficient. After conferring with my classmates and my teacher I have decided not to use copper wire
Constantan: constantan wire was easily accessible and it is available in many thicknesses. It is safe as long as the voltage is kept low.
After doing the preliminary experiment I have decided to collect readings every 5 cm use a starting wire of 100cm and use constantan wire.
Fair test & Safety
In order to make the experiment there are certain procedures that I must follow. I must use the same voltmeter, ammeter and constantan wire. This is in case other ammeters or voltmeters are using different settings.
To make the experiment safe we must check all wires and crocodile clips for faults. When we are doing the experiment we must also use a low voltage.
Method
- Collect apparatus: a voltmeter, an ammeter, 7x wires, 1 crocodile clip, and 100 cm constantan wire. (at lengths of 26 standard wire gauge, 28 standard wire gauge and 36 standard wire gauge)
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Set apparatus up as shown:
- Set the power pack on as low a voltage as possible. (So that there is not too high a current passing through the circuit.)
- Place the 100 cm of constantan round the holders. Then connect the crocodile clip.
- Turn on the power pack and record what the ammeter and voltmeter read.
- Record the results, in a pre prepared table.
- After recording all results for the 26swg piece of wire. Wait. Turn off the power pack. Take 28 SWG constantan wire. Turn on your power pack and record what the ammeter and voltmeter say.
- Change the wire to 36 SWG of constantan wire and repeat the experiment.
- Work out the resistance for all the results using Ohm's law. V = I*R
Obtaining evidence
Results for Constantan 26 SWG
Table 1
Table 2
Table 3
For the graph with all 3 tabled results for constantan 26swg see attached sheet 1.
Results for Constantan 28swg
Table 1
Table 2
Table 3
For the graph with all 3 tabled results for constantan 28swg see attached sheet 2.
Results for Constantan 36swg
Table 1
Table 2
Table 3
For the graph with all 3 tabled results for constantan 36swg see attached sheet 3.
Analysis
Analysis of length
“I predict that there will be higher resistance in wires that are longer in length”.
My prediction was correct. As the length of the wire decreases so does the resistance. This is clearly visible on all three of the graphs.
On the graph for constantan 26swg (sheet1) there is a strong negative correlation. The resistance for all three results at 100 cm is between
3.24 Ώ – 3.50 Ώ and at 5cm it is between 0 Ώ and 0.5 Ώ. From 65cm-40cm the results I collected are almost identical. There is hardly any variation in the results and it is shown by the graph.
The graph for constantan 28swg (sheet 2) is by far the best graph because of the closeness of all of the readings taken. There is a slight anomalous result at the 95cm reading. From the results collected in table 1 he resistance rose from 4.49 Ώ to 4.55 Ώ. This did not affect my results too much there was still a clear trend. This is however extremely unlike the graph for constantan 36swg (sheet3). There is clearly a huge error. At 90cm there is an incredibly out of position recording. The voltage for this point was 0.8 V. this is roughly 2.0 Volts away from where ideally it would be and this has caused such a dramatic change in the direction of the plotted points.
“I also believe that as the length doubles the resistance will also double.” My prediction was correct.
An example of this would be taken from table 3 of constantan 28swg. The length is 10cm and the resistance was 0.5 Ώ; the resistance for 20cm was 0.98 Ώ.
0.5 x 2 = 1 …………1 – 0.98 = 0.02
This is almost exactly double. This is only one example of the resistance roughly doubling with length.
Analysis of thickness
In order to analyse the thickness of the wire I will first need to work out the area of the wire. I have got the thicknesses in British Standard Gauge and I have found a site () which has a table with the thickness converted into millimetres. The conversions for the wires thickness’ are as follows:
Constantan 26swg = 0.457mm
Constantan 28swg = 0.376mm
Constantan 36swg = 0.193mm
This however is the diameter of each of the wires; and the formula for the area of a circle is π x r². The radius of a circle is half the diameter. To work out the area of the wire I must first halve the diameter then square it then multiply by pie. Pie (π) is 22 ÷ 7 the number has definite end.
Now I will work out the area for each of the wires.
Constantan 26swg:
0.457 ÷ 2 = 0.2285mm
0.2285² = 0.05221225mm
0.05221225 x π = 0.163946465 mm²
Constantan 28swg:
0.376 ÷ 2 = 0.188mm
0.188² = 0.035344mm
0.035344 x π = 0.11098016 mm²
Constantan 36swg:
0.193 ÷ 2 = 0.0965mm
0.0965² = 0.00931225mm
0.00931225 x π = 0.029240465 mm²
This shows that the Constantan 26swg is thicker than the Constantan 28swg and the Constantan 36swg and by how much in mm².
“I also believe that the thicker the wire is the less resistance will be present.”
This is correct. I have taken the resistance from all 9 tables and put them in a graph (sheet4). I have taken the resistance from 50cm for all of them. The graph clearly shows the huge difference in resistance. As you can see the Constantan 36swg is more resistant than the 26swg and 28swg Constantan wire. The area of the Constantan
Evaluation
