Planning Experimental Procedures
Planning Experimental Procedures
Introduction
In this experiment I will make a circuit using different materials of wires. To alter the length of the wire to be tested I will use crocodile clips. Voltage will be measured by using a voltmeter. Amps will be measured using an ammeter. Then the resistance is to be calculated.
Key Factors Identified
One variable should be carried out at a time, to make it a fair test.
I am going to investigate what factors affect the resistance of a wire. Here are the main factors, which affect the resistance of a wire and some reasons as to why they affect the resistance of a wire:
The material of the wire (What the wire is made out of)
The length of the wire
The thickness of the wire (The diameter of the wire)
Temperature of wires
Contact resistance
The material of the wire
The material of the wire is important because different metals have different properties. Metals, as wires are different because copper is very good at conducting electricity, if you had very large lengths of copper wire then you would be able to see the resistance change. Electrons find it easier to pass through some materials then others. I am going to use nichrome, copper, manganin and Constantan.
The material of the wire when cut should be clearly labelled to prevent it from being mistaken as another material.
The length of the wire
The length will make a difference because when you have a long wire the electrons have to squeeze together to be able to pass through the wire than they do to be able to pass through a short wire. The longer the wire the longer the current has to travel so each electron is more likely to collide with the other electrons, slowing them down, causing heat to be produced.
When cutting the wire, use a ruler and be as accurate as possible.
The diameter of the wire
The diameter is a variable because the wider the wire, the more electrons can pass through. More on the diameter of wire will be explained in the scientific theory.
The thicker the wire, the easier it is for the ions to pass through it. If it is too thick then there won't be enough resistance to take recordings of.
I will be using 24 SWG, which is 0.55 mm in diameter.
Temperature
The higher the temperature, the higher the resistance because heat speeds up conduction and therefore increases the rate of electrons flowing through the wire.
We cannot change the temperature so we will leave it at room temperature, which is 24?c.
Contact Resistance
Contact resistance is important. The resistance is also dependant on how much the components and wires etc. are making contact. Also the material of the crocodile clips is a variable. I assume the crocodile clips are made out of steel. Steel has a low resistivity rate.
Fair Test Described
To make my experiment as fair as possible I will change one variable at a time. For example I can not have one experiment using 5 cm of manganin 24 SWG at 0?c, and another experiment using 5 cm of manganin 34 SWG at room temperature (24?c). The data from this experiment is useless to me because although the material of wire and length is the same, the SWG and temperature is different. I will change one variable at a time. For example I will use 5 cm of manganin 24 SWG at room temperature, 10 cm of manganin 24 SWG at room temperature and 15 cm of manganin 24 SWG at room temperature. This is will be a fair test because I will be changing one variable at a time. And also changing one variable at a time will help me compare my data instead of having 2 variables different. I am going to control each of the variables. I will control variable one which is the material of wire by carefully reading the labels on the wires when choosing them so that I am picking up the wire which I am supposed to. I will control variable 2, which is the length of the wire by cutting it accurately. I will use a ruler and as I cut the wire I will cut it at 90 degrees so that each of the wires have the same diameter. I will control variable 3, which is the diameter of the wire by cutting the wire at 90 degrees as I have just mentioned for variable 2. I will control variable 4 by using a thermometer to keep the room temperature constant. As I carry out my experiment the wires will get hot and this will effect the results. A way of preventing this would be to do this experiment in a fridge. If I drilled a whole either side of the fridge and had my tested wire through there hooked up to the rest of the circuit then the temperature would be constant because when the wire did begin to heat up. The heat would then be immediately lost to the environment because the fridge is cool.
There is not much that I can do about variable 5 because it is about the contact of each of the components in the circuit. I cannot measure how much the components are in contact with each other because I have no device to do so.
Scientific Knowledge
I am going to investigate which materials of wire have the highest resistance and I will combine it with the investigation about which lengths puts up the greatest resistance.
Resistance is a property that restricts the flow of electric current through it. Current is a flow of electrical charged particles that goes around a conducting circuit, this is caused by the potential difference. The current at any point in a circuit is the amount of charge flowing per second. It is measured in amperes using A or Amps as its symbol. It carries electrical energy from a power supply, this could be a battery of a power pack to the components of the circuit, where it is converted into other forms of energy, heat light or motion. Resistance is measured in ohms using the Greek letter omega. In this experiment I will incorporate Ohms Law in my calculations. This law states the current flowing in a metallic conduction maintained at a constant temperature, directly proportional to the potential difference (voltage) between its ends.
I will be using Nichrome 24 SWG wire. Nichrome (Ni) is made up of nickel and chromium, and other materials include iron, magnesium, silicon and carbon but in small amounts. Nichrome has a high melting point and is resistant to corrosion.
Copper (Cu) is one of the most widely used metals. It is a transition metal and has a high melting point
Manganin contains manganese, copper and nickel. It is mainly used in the form of wire for accurate electrical measurements because its electrical conductivity does not vary appreciably with temperature.
24 SWG is equal to 0.55 mm in diameter.
From doing my research into resistance of wire I have found that...
As the length increases
the resistance increases.
The graph on the left shows us this.
As the diameter increases
the resistance decreases.
The graph on the left shows us this.
The diagram on the right is a water
circuit; the pump is pumping water
around the circuit. As the water
passes through the wide pipe (Y) it
flows quicker than it does through
narrow pipe (X). This is because
water can flow through wider pipes.
Electrons pass around any circuit from the negative terminal to the power pack or battery to the positive terminal.
The rate at which the water is flowing is the current in an circuit how fast are the electrons moving. Resistance is what restricts the movement of the charge through the wire. The length of a pipe and its the cross-section, all prevent the flow of the water, and are associated to how electric current is impaired as it flows through a wire. Things like making the wire longer and thinner make the resistance go up since it is harder to push charge through the wire. Sometimes, some materials can be cooled down to very temperatures where they have effectively zero resistance, but in everyday encounters, effect doesn't really have much bearing.
The reason for resistance in wire is because of the composition of the atoms such as copper, aluminium, of which a particular wire is made of and the arrangement of the atoms of these metals. When an electron passes through the wire, the electrons hit these atoms while making the journey from one end to the other giving opposition or resistance to the electrons.
When volt electrons move along the wires they hit atoms which creates heat through friction of the electrons and atoms.
Free electrons are attracted towards positive protons in the nucleus. ...
This is a preview of the whole essay
The reason for resistance in wire is because of the composition of the atoms such as copper, aluminium, of which a particular wire is made of and the arrangement of the atoms of these metals. When an electron passes through the wire, the electrons hit these atoms while making the journey from one end to the other giving opposition or resistance to the electrons.
When volt electrons move along the wires they hit atoms which creates heat through friction of the electrons and atoms.
Free electrons are attracted towards positive protons in the nucleus. The more protons there are the greater the attraction, the greater the resistance.
Below is a diagram showing that if the length of the wire is longer then it takes more time for the electricity to pass through it because it bumps into atoms in the wire through which they pass. Atoms of different elements prevent the electrons to different extents.
Shorter Wire Longer Wire
When an electric current passes through thin Nichrome, Constantan or manganin wire the electrons cannot flow easily, the diagram below shows the difference between a thin wire and a thick one.
Thin wire
Thick wire
Plan
I am going to be experimenting with 10 different lengths of wire, I will carry out each experiment three times.
. Collect apparatus: a voltmeter, an ammeter, wires, crocodile clips, thermometer, 5,10,15, 20,25,30,35,40,45 and 50 cm of nichrome, Constantan, manganin and copper wires and a power pack. The power point will supply 4 volts direct current constantly around the current.
2. Set apparatus up as shown:
3. Experiment with the Nichrome first, test each length of the wire and record down the results from digital ammeter 1, analogue ammeter 2 and digital voltmeter 1.
4. Turn off the two digital metres and disconnect all the wires
5. Reconnect all wires and turn on the meters.
6. Record the meter readings again until you have 3 sets of recordings for each wire.
Suitable number and range of observations planned
I intend to measure the resistance of 10 different wire lengths. I will start from 5 cm and I will increase this number by adding 5 each time until I have measured the resistance for 50 cm of wire. The lengths that I choose to measure will be sequential so that when I am analysing the data I will be able to look at the proportions, and also to help me quantatize. I will use 2 different ammeters (analogue and digital). This is to make my final results more accurate. And to be even more precise I will carry the experiment out 3 times to give me an even more accurate average to get rid of the effect of any anomalous results.
Detailed Scientific Knowledge used to Plan
Whilst carrying out the experiment the wires that are being tested will become very hot. The longer the wire used the hotter the wire will become. Because I am using 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 cms of wire I have considered health and safety. If I was to be adventurous and use 1 m, 2 m and 3 m's etc. then the wires would become very hot because there is further for the electrons to travel, they would clash which would cause heat energy to form, this could cause a fire risk. And also if I were to use long lengths then it would be expensive. A way of preventing the heating effect would be to conduct this experiment in a fridge. If I drilled a whole either side of the fridge and had my tested wire through there hooked up to the rest of the circuit then the temperature would be constant because when the wire did begin to heat up. The heat would then be immediately lost through because the fridge is cool. I would like to carry out my experiment this way but I lack the vital resources, which I need for this theory to work.
Precision
When doing this experiment I wanted to be as accurate as possible to collect the best set of readings that I can, to achieve this,
* When I measure the wires to test their resistance I will use a ruler and try to be correct in measuring, then I will ask a member of my group to double check the length of the wire to see if I am correct in measuring.
* Once the wires have been cut to save confusion I will label them with their SWG, length and material of wire.
* I will try 2 different ammeters, analogue and digital. I will do this to be as accurate as possible. By using 2 different ammeters I will be exact. After I have read both of the metres, I will find out the amp average by adding them together and dividing by 2 and so decreasing the effects of anomalous results.
* Once I have read the digital ammeter, analogue ammeter and the digital voltmeter, I will switch off all the meters and disconnected all the wires from each other. Then connect the circuit up again and switch on all of the meters, so that I can get another reading. I will carry this out 3 times to get 3 sets of results, so that I can find out the amp average and volt average, to be as accurate as possible.
* I will use a variable resistor to keep to current low to avoid heating effects. I need to keep the experiment safe. I will avoid fire hazards.
Prediction justified by Scientific Theory
From the scientific knowledge that I have
gathered, I can predict that, the longer the
wire the longer the electrons have to stay
squashed together, and so the longer they
take to pass through the wire and higher the
resistance. On the right is a sketch graph of
what I predict. I predict that if the resistance
for 10 cm is 0.5 ohms, the resistance for 20cm
is 1.00 ohms and the resistance for 40cm is
2.00 ohms. I predict that as the length doubles, the ohms will as well. I might not be accurate on the numbers, but I am just predicting the trend.
I predict that when I try the copper wire it will be very hard to collect results because the readings from 5cm-50cm will not have a big difference. Copper has a very low resistance, so there will be a large current.
I predict that the nichrome, Constantan and manganin wires will all have a higher resistance than the copper wire. I can say this because I know that the electrons have to squeeze together more in order to be able to pass through nichrome wire than they do in order to pass through that copper wire.
I predict that the higher the temperature of the wire, the faster the rate of electrons flowing through it because heat speeds up conduction.
I predict that if there is less contact between each of the wires then fewer electrons pass through the wire therefore more resistance.
When analysing my data I hope to find a quantitative pattern. I predict that as the length in wire doubles the resistance will hopefully double. There will be some parts of the data that are not quantitative, this could be because of my lack of precision etc.
Secondary source
Candidate number 7015 has given me her data so that I can compare it to mine. I trust her to have carried out this experiment fairly and accurately.
I will put the data gained from the other candidate into a graph, which can help me compare my results to hers. I will be looking at a secondary source to show me how accurate I have been with my careful planning.
I used Focus Educational Software to give me more background information on resistance. I was able to do the experiment on the computer using the software. When I came to testing copper wire, I had realised that if I were to do this experiment then using copper would be a waste of time because the resistance is so low that I would have to use large amounts of it to see any difference.
Obtaining Evidence
Systematic and Accurate Observations made
I obtained a good set of results in my opinion because I was as accurate as I could be. I tried my hardest to stick to the precision that I have mentioned in the previous section. I repeated my results 3 times. My results do make sense at a glance because as the length increases the resistance does.
I attempted to investigate the resistance of copper wire. The resistance was so small that if I were to see a difference in resistance then I would have to use very large amounts of copper wire. If I did use large amounts of copper wire then there would be a fire risk, and also copper wire is very expensive.
My Results for Nichrome 24 SWG
Length (CM)
Manual Current Average (Amps)
Digital Current Average (Amps)
Average Current
(Amps)
Potential Difference Average (Volts)
Resistance
(Ohms) ?
5
0.62
0.58
0.6
0.16
0.26
0
0.58
0.56
0.57
0.28
0.49
5
0.54
0.53
0.535
0.41
0.76
20
0.5
0.48
0.49
0.57
1.16
25
0.5
0.48
0.49
0.63
1.29
30
0.48
0.45
0.465
0.76
1.63
35
0.48
0.44
0.46
0.81
1.76
40
0.46
0.43
0.445
0.87
1.95
45
0.42
0.41
0.415
0.95
2.29
50
0.42
0.4
0.41
.04
2.54
Secondary Information for Nichrome 24 SWG
Length
(CM)
Average Current
(Amps)
Potential Difference Average (Volts)
Resistance
(Ohms) ?
5
0.7
0.15
0.21
0
0.6
0.3
0.5
5
0.55
0.4
0.72
20
0.5
0.6
.12
25
0.49
0.6
.22
30
0.45
0.75
.66
35
0.46
0.81
.76
40
0.44
0.85
.93
45
0.42
2.38
50
0.41
.04
2.54
My Results for Manganin 24 SWG
Length (CM)
Manual Current Average (Amps)
Digital Current Average (Amps)
Average Current
(Amps)
Potential Difference Average (Volts)
Resistance
(Ohms) ?
5
0.51
0.46
0.485
0.046
0.094
0
0.49
0.44
0.465
0.09
0.19
5
0.46
0.42
0.44
0.12
0.27
20
0.44
0.41
0.425
0.17
0.14
25
0.42
0.41
0.415
0.2
0.48
30
0.42
0.4
0.41
0.21
0.51
35
0.42
0.42
0.42
0.27
0.64
40
0.42
0.4
0.41
0.31
0.75
45
0.42
0.39
0.405
0.36
0.88
50
0.4
0.38
0.39
0.37
0.94
Secondary Information for Manganin 24 SWG
Length (CM)
Average Current
(Amps)
Potential Difference
Average(Volts)
Resistance
(Ohms) ?
5
0.48
0.045
0.094
0
0.46
0.09
0.19
5
0.44
0.12
0.27
20
0.43
0.17
0.14
25
0.42
0.2
0.4
30
0.41
0.21
0.51
35
0.42
0.27
0.64
40
0.41
0.31
0.76
45
0.4
0.36
0.9
50
0.35
0.35
My Results for Constantan 24 SWG
Length (CM)
Manual Current Average (Amps)
Digital Current Average (Amps)
Average Current
(Amps)
Potential Difference Average (Volts)
Resistance
(Ohms) ?
5
0.6
0.58
0.59
0.06
0.1
0
0.58
0.54
0.56
0.12
0.21
5
0.53
0.53
0.53
0.16
0.3
20
0.54
0.53
0.535
0.21
0.39
25
0.53
0.52
0.525
0.26
0.49
30
0.52
0.5
0.51
0.3
0.58
35
0.51
0.5
0.505
0.36
0.71
40
0.49
0.49
0.49
0.44
0.89
45
0.51
0.5
0.505
0.46
0.91
50
0.49
0.48
0.485
0.49
1.01
Secondary Results for Constantan 24 SWG
Length (CM)
Average Current
(Amps)
Potential Difference Average (Volts)
Resistance (Ohms) ?
5
0.6
0.06
0.1
0
0.5
0.1
0.2
5
0.55
0.15
0.27
20
0.53
0.2
0.37
25
0.54
0.25
0.46
30
0.5
0.4
0.8
35
0.5
0.3
0.6
40
0.49
0.44
0.89
45
0.5
0.45
0.9
50
0.48
0.49
.02
Here is a step by step plan of how I recorded my results,
. I recorded the readings from the analogue ammeter 3 times.
2. I found the analogue average, by adding the 3 results and dividing by 3.
3. I recorded the readings from the digital ammeter 3 times.
4. I found the digital average, by adding the 3 results and dividing by 3.
5. I added the digital and analogue ammeter together and divided by 2 to find the amp average.
6. I recorded the volt meter readings 3 times
7. I found the average of volts.
8. I divided the amp average by the volt average to give me the resistance in Ohms.
9. I swapped my results with another group so that I could later compare the results in my write up.
There aren't many anomalous results. I have circled the anomalous results.
I followed this step plan for recording results for 24 SWG of Manganin, Constantan, and Nichrome.
The secondary data only has the average numbers because I do not need to have every single recording of the other person's data, I have enough information because I have their averages.
Precision
I attempted to be as accurate as possible as I said in my previous precision. I was being accurate by...
* When I measured the wires to test their resistance I used a ruler to be correct in measuring, then I asked a member of my group to double check the length of the wire to see if I was correct in measuring.
* Once the wires had been cut to save confusion I labelled them with their SWG, length and material of wire.
* I used 2 different ammeters, analogue and digital. I did this to be as accurate as possible. By using 2 different ammeters I was exact. After I had read both of the metres, I found out the amp average by adding them together and dividing by 2, I did this to decrease the effects of anomalous results. I kneeled down onto one knee and I accurately read the meter by meeting my eye level with the needle for the analogue meters, I did this to avoid parallax error.
* Once I had read the digital ammeter, analogue ammeter and the digital voltmeter, I switched off all the meters and disconnected all the wires from each other. Then I connect up the circuit up again and switch on all of the meters, I did this 3 times to get 3 sets of results, so that I could find out the amp average and volt average, to be as accurate as possible.
* I used a variable resistor to keep to current low to avoid heating effects. I kept the experiment safe, the wire did heat up but not enough to cause a fire.
I think that the results that I obtained where a good set because I was fair, accurate and I calculated the averages.
Reliable Evidence Obtained
The sets of results, which I gathered, are in my opinion as accurate as I could get them. This is because I picked the best equipment that was available to me and I used them properly and accurately. I have circled the anomalous results, there is not that many, this proves that my precision was extremely accurate. I averaged of all my results before I worked out the resistance. I thought that this was the best way to use my results to be accurate. I received data from candidate number 7015, I trust her and know her well. I believe that she has carried her experiment out as best as she could.
Appropriate Number and range of observations made
I chose to use 5, 15, 15, 20 25, 30, 35, 40, 45 and 50 cm's of wire. These numbers have a 5 cm interval I could have chose to have 10 cm intervals but I thought that using 5 would be more accurate. If I chose to have random intervals for example, 5, 8, 9.9, 40 cm's of wire then my volt and amp readings would be no use to me because there would be no use in analysing the data. If I didn't have suitable intervals between my lengths then I would not be able to quantatize.
Analysing Evidence
Numerical Methods used to process evidence
I had to get the amp and volt readings to find out the resistance. To work out the resistance I used the formula,
r=v?i
I will give an example of how I worked out my averages and applied the formula to my work.
If you look at column 2 and 3 of the table below, you will see the average current results. To get a final average of the amps I added these together and divided it by the number of items which is 2. Here is the calculation-
0.62+0.58=1.2
.2?2=0.6
Therefore my final average for amps is 0.6 amps.
This is where I need to apply the formula, I have the average amp data and the average volts, I need to divide the two to get the resistance,
r=v?i
r=0.16?0.6
r= 0.2666666666667
r= 0.26 (2 d.p.)
Length (CM)
Manual Current Average (Amps)
Digital Current Average (Amps)
Average Current (Amps)
Potential Difference
Average (Volts)
Resistance
(Ohms) ?
5
0.62
0.58
0.6
0.16
0.26
I used this formula to work out all of the resistances. I got another member of the class to check my calculations to double check it. If I wanted to work out the volts or amps using the formula then I would rearrange it.
If I wanted to work out the volts using the resistance and amps then I would make v the subject,
r=v?i (?i)
r?i=v (swap them around)
v=r?i
I have also made I, the amps the subject of the formula...
r=v?i (?i)
r?i=v (?r)
i=v?r (swap them around)
I have put all of my results into graphs-I have 2 graphs.
. My results for constantan, manganin and nichrome 24 SWG
2. Secondary results for constantan, manganin and nichrome 24 SWG.
I plotted the averages of resistance on the first graph, the second graph has my secondary data on it. To analyse this data I will find the equation for each of the lines.
To find out an equation of any line I need to use the formula,
y=mx+c
x represents the gradient of the line,
c represents where the line of best fit hits the y intercept,
y represents the value on the y axis
x represents the value on the x axis
I had a total of 6 lines of best fit, this is because, 3 of the lines where from my own results and the other 3 lines where from a secondary source (another group).
Below is a table of the gradients of each of the lines.
Material
Gradient- My Results
Gradient- Secondary Results
Nichrome
0.45
0.7
Constantan
0.3
0.65
Manganin
0.7
0.4
The gradient of a line tells me how steep the line is. The higher the gradient the steeper the line.
I have found out where each of the 6 lines hit the y axis.
Material
Y Intercept- My Results
Y Intercept- Secondary Results
Nichrome
0.02
0.07
Constantan
-0.02
-0.05
Manganin
-0.02
-0.05
Now that I have the gradient and y intercept of each of the lines I can now put them into an equation.
Material
Equation- My Results
Equation- Secondary Results
Nichrome
y=0.45x+0.02
y=0.7x+0.07
Constantan
y=0.3x-0.02
y=0.65x-0.05
Manganin
y=0.7x-0.02
y=0.4x-0.05
These equations mean that if I want to find out the resistance for nichrome 24 SWG for example then I would choose the length that I have and put that number as x,
If the length (x) is 100cm then I would put this into the equation which is,
y=0.45x+0.02
y=0.45?100+0.02
y=45+0.02
y=45.02
45.02? is the resistance that I would get if I had 100 cm of nichrome.
Conclusion Drawn from Processed Evidence
Both graphs have a positive correlation, this means that the plotted points are near to a straight line which has the equation of y=x. Because I have a positive correlation this means that the x axis is directly proportional to the y axis. As you can see from the gradients and graphs, the secondary results and my own are very similar, this proves that I was fairly accurate because another group had very similar results to me. Nichrome wire has a very steep slope compared to manganin and constantan. This shows that manganin has higher resistance then the other 2 metals. Manganin and constantan are very similar in resistance because the gradients are similar and the y intercepts are almost identical. There is a slight difference between the gradients of my data and the secondary data. I was not expecting them both to be identical because although we had the same plan the equipment we used was different.
If you look back at the previous page you can see the table which has the equations for the line of best fit, for my own results and the secondary. Overall, Nichrome wire has the highest resistance, manganin and Constantan wire are very similar in resistance.
Relate to Scientific Knowledge and Prediction
Below are tables, which have the numbers for each of the A, B and C points for my data.
Nichrome
Length
Resistance (actual results)
Previous Resistance?2 (my prediction)
Point A
0
0.64
Point B
20
.8
0.64?2=1.28
Point C
40
.95
.8?2=3.6
manganin
Length
Resistance (actual results)
Previous Resistance?2 (my prediction)
Point A
0
0.18
Point B
20
0.38
0.18?2=0.36
Point C
40
0.76
0.38?2=0.76
Constantan
Length
Resistance (actual results)
Previous Resistance?2 (my prediction)
Point A
0
0.18
Point B
20
0.4
0.18?2=0.36
Point C
40
0.82
0.4?2=0.8
Earlier in my investigation I made a quantitative prediction that as the length doubled, the resistance would. I found these A, B and C points by looking at the graph which represented my data and then looked along the x axis to find 10, 20 and 40 cm. And then by drawing a vertical line going upwards until it reached the line of best fits. I read off the line horizontally to get the ? reading. I picked the lengths, 10, 20 and 40 cm's because 10 doubled is 20 and 20 doubled is 40 cm. I picked these lengths so that I could easily find a quantitative pattern. I predicted that as the length in wire doubled, the resistance would also double. For Nichrome wire at point A, which is at 10 cm, the resistance is 0.64, I expect this to double to give me the resistance for point B which is 20 cm long. 0.64?2=1.28. The actual result that I got was 1.8. 1.8 and 1.28 are not that far apart, I could say that I was correct in predicting this. But I have definitely proven my prediction correct for the manganin and Constantan wire. Point A manganin, 10 cm, the resistance is 0.18?. Point B manganin, 20 cm, the resistance is 0.38?, the resistance has nearly doubled. Constantan, point A, 10 cm, the resistance is 0.18?, point B, 20 cm is the resistance of 0.4. This has also nearly doubled. Point C, 40 cm Constantan the resistance is 0.82. This has also nearly doubled. For most of the wires I can clearly say that the resistance doubles as the wire does. My prediction was correct even though the numbers where far out. I predicted that the 'doubling trend' would occur, and it did.
In section one, I gathered scientific knowledge so that I could make a prediction. In my scientific knowledge I found that as the length increases, the resistance increases, because when the wire is lengthened, the journey is considerably longer and the resistance is increased. I also researched into other areas as well as the length of wire. I am not going to mention them again here because I did not investigate into them. In my investigation I mainly focused on the length of the wire.
Explain conclusions using theory
The reason to why the resistance increased as the length did was because the electrons have much further to travel. When volt electrons moved along the wires they hit atoms which created heat through friction of the electrons and atoms. The free electrons were attracted towards positive protons in the nucleus. The more protons that there where the greater the attraction, therefore greater the resistance.
It took more time for the electricity to pass through the longer wires because it bumped into atoms in the wire through which it passed
Prediction supported by results
I made a number of predictions in section one, only one of them applied to the investigation that I was doing. This was the prediction linked with the length of wire. It was the only variable that I experimented with. I predicted that, the longer the wire the longer the electrons have to stay squashed together, and so the longer they take to pass through the wire and higher the resistance. I drew a sketch graph, the actual graph that I constructed was similar to the predicted one. They both had positive correlation. I also predicted that if the resistance for 10 cm is 0.5 ohms, the resistance for 20cm is 1.00 ohms and the resistance for 40cm is 2.00 ohms. I predicted that as the length doubles, the ohms will as well. I was not accurate on the numbers, but the trend was correct. As the length doubled so did the resistance in ohms. My results have definitely shown that the resistance doubles as does the length. Overall my predictions where accurate because they were based on my scientific knowledge. I predicted that Nichrome, Constantan and manganin wires will all have a higher resistance than the copper wire, I was correct in predicting this because when I experimented with the copper wire it did not record many ohms.
Evaluating Evidence
Comment of Accuracy of Observations
I think that the experiment went according to plan. I tried hard to keep to my precision. My final results are very accurate because they are very similar to the secondary results. The way in which I did my graphs was wrong. I should have ended up with three different resistance calculations instead of one. If I did have three resistance calculations then I could have plotted three crosses and looked at how far apart each set was. If a set was close together then I would know that I am accurate, but if the range of the plots were far apart then I know that I have collected appalling results!
Anomalous Results Recognised
Manganin 24 SWG from my results has one anonymous result which is for 20 cm.
I can successfully say that I have proven my prediction to be correct.
There were a few anonymous results on the final graphs, these are considered to be normal because every experiment has anonymous results. Although these stood out, I still came out with a line of best fit, which suited my prediction. The temperature played an important role because I may have taken a particular set of results quickly while the wire was still warm. I might have misread the meters, or I could have made an error when working out the resistance. I have circled the anomalous results which you can find in the tables in section 2.
Comment on Suitability of Procedure
There was only one thing, which really affected this investigation-the heating effect. The more I used the wires, the hotter they became. The higher the temperature of wire, the higher the resistance because heat speeds up conduction and therefore increases the rate of electrons flowing through the wire. I would have liked to conducted this experiment in a cool place, i.e. in a refrigerator. If I had a fridge available to met then I would have used it. If the experiment were done in a fridge then the heat emitted from the wires would have been lost to the environment (the fridge). As the length of the wire increased, so did the resistance. I believe that this was actually because of the length of the wire-electrons have further to go. I do not think that the resistance increased because of the heating effect.
Suggest improvement to the test was carried out or why no improvement needed
The only improvement needed here is to do with the heating effect, I would have like to have carried out this experiment in the fridge, If I had the chance to. but if I could do the whole experiment again then I would choose to carry out each part of the experiment out 5 times and not 3, so that there would be less anomalous results.
And of course I would like to have done this experiment in cooler conditions.
Comment in detail on reliability of evidence and results-discusses how well variables have been controlled or not
I believe that I carried this investigation out as thoroughly and as accurate as I could do it, because I had a critical precision list which I kept close to. To change the length of the wire, which was the variable that I choose to investigate, I started off with a 55 cm long wire of the chosen materials, which could have been Constantan Nichrome or manganin. I first measured 5 cm along that piece of wire and put the crocodile clip at the 5 cm point, that I could find out what it's resistance was. In order to control this variable, first of all I measured 5 cm of the wire and the so did another member of my group to double check it. I also labelled each of the wires as soon as they been cut to avoid confusion. I believe that I controlled the variables quiet well. The results are reliable because they are similar to the secondary results and also they match my scientific knowledge. The two different ammeters and the averaging process make my results reliable. I used two different ammeters, digital and analogue so that I had a reading for each meter which I then made and amp average of to reduce the effect of any anomalous results.
Detailed comment on whether evidence supports a definite conclusion
The evidence supports a definite conclusion which is as the length increases so does the resistance. I know this because if you look back to section 2, at the table of results there is an obvious trend, which supports my conclusion. I can definitely conclude that as the length of the wire increases do does the resistance.
Propose improvements which would provide additional evidence
To find out how accurate my results are, I could find out the resistance for a wire which is 2.5, 7.5, 12.5, 17.5, 22.5, 27.5, 32.5, 37.5, 42.7 and 47.5 cm long. And then I could plot the resistance on my results for these onto the graph which is in the obtaining evidence section, and see how far away the results is from my line of best fit. If the results were quiet close to the line of best fit then I would know that I have accurately worked out the line of best fit and also that my results are first set of results which go up in 5's are accurate. I think that going up in 2.5 cm's is a suitable range because it is half of the previous range that I had which was 5 cm.
Suggest how you could extend your enquiry into other areas
There are many way of extending this experiment...
I could have used different SWG wires as well as 24 SWG. I could have found out why the resistance changes as I increase/decrease the SWG. I could have had a different amount of voltage (DC) going around the circuit, I could investigate what happens as I increase/decrease the voltage. I could use other materials other than copper, manganin, Constantan and Nichrome. I could have used gold, which has a very small resistance because it is a good conductor. Instead of changing the length by increasing it by 5 each time I could repeat the same experiment but going up in 2.5's instead of 5's. But if I did have another chance to repeat this experiment then I would conduct this experiment in a fridge so that the heat made from the clashing electrons will immediately be lost before they can have any effect on the electrons.
I could have researched into contact resistance. I could have found out how much the resistance is changed if there is more/less contact around the circuit. This diagram is an example of contact resistance. In the experiment I used crocodile clips, but if used a razor blade or something similar amp and volt reading could be different, and that would make the resistance different.
This diagram show the grey crocodile clips representing the crocodile clips, which have a larger surface area contacting the actual wire, and the larger the surface area, the larger the resistance. However if the conductors with small surface areas were used i.e. the razor sharp blades, then the resistance could have been less.
The resistively of the metal of the crocodile clip is another factor to investigate into.
Science Coursework-Physics
Chandni Ladva