Investigation on the Resistance of Nichrome wire

GCSE Science

Lucy Kennington C2

Planning

Variables

Voltage
Current
Length of wire
Apparatus used in the circuit
Temperature of room
Thickness of wire
Temperature of wire
Material that the wire is made from

Investigating how changing the length of Nichrome wire affects the resistance

Apparatus

1000mm Nichrome wire
2 leads
2 Crocodile Clips
Multimeter (Battery operated)
1000mm Ruler
Thermometer
Sellotape

Preliminary experiments

I carried out a preliminary experiment to find out which apparatus would be best suited to find the resistance of Nichrome wire, to see the other factors that could affect the experiment and also to see if I could improve any of the steps in the method.

I began by setting up two circuits, the first with a multimeter and the second with a power pack, I wanted to see which one would be more accurate for my investigation. Using a multimeter is more accurate because it keeps the current going through the circuit low which keeps the temperature of the wire just about the same, this means if the wire is not heated and so the particles of atoms and electrons will not collide as frequently which therefore will not convert as much kinetic energy into heat which could affect the results. The multimeter will have the same current because of the fuse, the fuse only lets up to 0.25A flow through any circuit, this is a low current so it will not give the wire a noticeable heating affect although there is very little temperature change, but it would not affect my investigation.

If I used the power pack to find the resistance of the wire I would have to wait for the wire to cool down in between each reading for consistency, this is because as soon as the power pack is turned on the wire had already began to get hot so the heating affect works very quickly. I know this because I could feel or measure with a thermometer the difference in temperature of the wire to when it was not connected to the power pack. If I did that it would not be as accurate as using the multimeter because the wire is hot. The resistance changes and makes it more difficult for the electrons to travel along the wire, this means the electrons are colliding more frequently.

To test the resistance of the wire is the same throughout, I set up a circuit containing two leads, two crocodile clips, multimeter and Nichrome wire attached to a ruler. I then put the crocodile clips onto the wire at intervals of 100mm going from 0mm to 100mm all the way up to 1000mm. This shows that the wire’s thickness could be the same throughout because the flow of electrons and atoms colliding is the same because it gives off the same resistance.

I will use 100mm intervals because the meter ruler easily measures them, give a good range and give me a noticeable difference. If I only increased the distance by 50mm, that would give me results like, 0.6ohms, 0.7ohms and 0.8ohms. If this happened in my real experiment that would not be very reliable because 0.7 ohms could be anything from 0.65ohms to 0.74ohms and the 0.8ohms result could be anything from 0.75ohms to 0.84ohms, this would mean that my results only had a 0.01ohms increase so there would hardly be any noticeable change in resistance. Also in my preliminary experiment I used the multimeter, two crocodile clips and two leads to find the resistance of the leads and crocodile clips. It gave me a reading of 00.3ohms. I needed to do this because it could affect my graph of results when the crocodile clips are at 0mm it would still give a reading of 00.3ohms.

I have also chosen to take 3 repeats at each length and then take an average. I have chosen this so that if I have any anomalous results they will not show when I plot the averages on the graph.

In my main experiment instead of using an ammeter and voltmeter I have chosen to use an multimeter, I have done this so that I am going to use the multimeter for my experiment because it is easier to use and it does not significantly heat the wire. The multimeter gives a direct measurement of resistance so therefore I think the multimeter will be more reliable and accurate.

Method

To do my experiment I will…

Set up the apparatus as shown in the diagram on page 1.

Attach the Nichrome wire to a 1000mm ruler with sellotape. (This will make my measuring accurate because I will be able to see where to put the crocodile clips and it will hold the wire in one place.) I need to keep the wire straight because if it were bent the length of the wire would have increased affecting the investigation.

Start measuring the resistance by starting at 0mm-0mm and increase by 100mm each time e.g. 0mm-100mm. (I will do this because from my preliminary experiments I found that increasing the length by 100mm each time gave me a noticeable change in resistance).

Switch on the Multimeter (which is connected to the Nichrome wire via the crocodile clips). Record the reading I get from the Multimeter and switch off the Multimeter. (This will save the battery, which will give me more accurate results.)

Increase the length by 100mm until I reach 1000mm. This will give ...

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Start measuring the resistance by starting at 0mm-0mm and increase by 100mm each time e.g. 0mm-100mm. (I will do this because from my preliminary experiments I found that increasing the length by 100mm each time gave me a noticeable change in resistance).

Switch on the Multimeter (which is connected to the Nichrome wire via the crocodile clips). Record the reading I get from the Multimeter and switch off the Multimeter. (This will save the battery, which will give me more accurate results.)

Increase the length by 100mm until I reach 1000mm. This will give me a wide range of results to draw a graph.

Repeat the whole experiment two more times making sure I use the same pieces of apparatus so nothing changes to make my experiment fair.

Take an average of the three sets of results (so that any anomalous results they will not show when I plot the averages on the graph).

Draw a graph and conclude the result that I have found.

How I will ensure my measurements are as accurate as possible

I will make sure my measurements of length are as accurate as possible by sellotaping down the Nichrome wire flat to a ruler. This will make my experiment accurate because it will ensure that I can accurately measure the length that I am going to increase it by. The length by which I increase the crocodile clips must be accurate and precise because the investigation is about finding what affect wire length has on resistance.

How I will ensure my investigation is as fair possible

In my experiment I used a multimeter so the voltage in the circuit stayed the same at 9V. This means that throughout all of my experiment the voltage will be the same so that it will be fair.

The voltage in the circuit will stay the same and so will the current. This is because the battery, which is 9V, is controlled by the multimeter. The current is low which is good because this will not significantly heat the wire, so the results would be accurate. I will have to keep the voltage low to minimise resistance. “This is due to kinetic theory, the more voltage, the hotter the wire, the spaces in the wire are less due to the particles moving more and there is more chance of a collision.”(1)

The length of the wire will go up in 100mm intervals and will be measured with a ruler so that it is accurate. For each experiment the same bit of Nichrome wire will be sellotaped to the same ruler to make sure I use the same apparatus. This will make my experiment more reliable.

In the circuit will be two leads with crocodile clips, a multimeter and the Nichrome wire. I could measure the resistance of the leads and crocodile clips, and I could compensate for the resistance of the leads and clips in my results. The graphed points should give a line that goes through the origin. Where the line crosses the y-axis this gives the resistance of the leads and clips.

To make sure the heating effect does not affect the wire I will make sure I complete my three experiments within 15minutes on the same day. The three experiments only take 15 minutes each time to complete and if they are done at the same time they would give more accurate results than if they were done at different times. I will also be using a thermometer to measure in degrees the temperature of the room.

The thickness of the wire is 0.45mm. I can also tell this by measuring lengths of 100mm each time and testing the resistance is the same for each length of the wire I used. This is fair because if the wire were different thickness’ it would give me inaccurate results. Although the longer the length the higher the resistance, if the wire is thick its resistance is lower because its just like a resistor and works in parallel and lets the current through easily. I think that if the wire width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.

I cannot measure the temperature of the wire but the current going through the circuit is not high enough to give a significant heating affect. This will keep my experiment fair because the wire will stay the same temperature, which will not affect its resistance. I think that if the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. “This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons.”(1) This increase in collisions means that there will be an increase in resistance.

The material used is Nichrome wire. This will be the same piece of wire for each experiment so it is accurate. I think that the material of the wire will affect the amount of free electrons, which are able to flow through that wire. This is because the number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. “If the material has a high number of atoms there will be high numbers of electrons causing a lower resistance because of the increase in the number of electrons.”(1) Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.

Predictions

I predict that the longer the length of the wire the higher its resistance, if the length increases then the resistance will also increase in proportion to the length. This is provided that the thickness of the wire is kept constant.

I also predict that as the cross-sectional area of the wire doubles, the resistance will half.

If you subtract the resistance of the two leads and the two crocodile clips from the resistance measured during the experiment, I found that then the graph would go through the origin.

Justifications

The reason for my prediction is because the longer the Nichrome wire, the more atoms, which means a greater chance of electrons colliding with the atoms. The number of collisions will slow the flow of electrons down (because the electrons loose some of their energy) and increase the resistance. “Free electrons are created, which carry a negative charge, to jump along the lines of atoms in the Nichrome wire. Resistance is when these electrons, which flow towards the positive, collide with other atoms; they transfer some of their kinetic energy.”(1) This transfer on collision is what causes resistance. “As electrons pass through the wire, the electrons hit the atoms of the wire whilst making the journey from one end to the other, giving opposition or resistance to the electrons.”(1) When this happens it also creates heat via friction of the electrons and atoms. When the wire is lengthened, the journey is longer and the resistance changes in proportion.

As the cross-sectional area of the wire doubles, the resistance will half. There would be twice as many ions and twice as many electrons bumping into them, but also twice as many electrons getting through twice as many gaps. If there are twice as many electrons getting through, there is twice the current, the resistance must have halved. The thinner the wire is the less channels of electrons in the wire for current to flow, so the energy is not spread out as much, so the resistance will be higher: We see that if the area of the wire doubles, so does the number of possible routes for the current to flow down, therefore the energy is twice as spread out, so resistance might halve.

I think the graph will be like the shape I have drawn it because I predict the longer the wire the higher the resistance and because I think the resistance of wire will go up by the same amount each time. I think the graph will be straight in a diagonal line going to the right. The graph line does not go through the origin because even if I were to place the crocodile clips on the wire at 0mm there would still be a resistance because of the resistance of the leads. The graph would go through the origin if I took away the resistance of the leads and the crocodile clips, this would not give an accurate drawing of the graph though because when the crocodile clips are touching and connected in the circuit with the multimeter there will always be some resistance due to the leads.

Bibliography

(1) = Internet resources

Table of Experiment Results

Averages used to plot results

Conclusion

The longer the length of Nichrome wire, the higher the resistance.

From my graph I have shown that my prediction was correct, as the line of best fit is a straight line, this proves that the resistance of the wire is proportional to the length of the wire. The length of the wire also affects the resistance of the wire, because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion.

The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions, which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also be increased.

I have come to this conclusion because at 0mm-100mm the resistance of the wire is 1.0 ohm if I look at 0mm-600mm the resistance is 4.7ohms.

The shape of my graph is in a straight line. The rate of change is the same as it goes up. I know this because the line of best fit is straight and goes up by about the same amount each time and can join most my points up apart from four, which does not fit (this could be down to an error in the measurement of the wire or a temperature rise). Although by taking more than one result then calculating the average increased the reliability of my results and meant that in my graph I had no major anomalies.

I got these results because if the resistance of wire is 1.0ohm whichever part of the wire you pick where the distance between the crocodile clips is 100mm, it should go up by the same amount each time if you increase the length from the start by 100mm. This is why I think that it goes up in a straight line, because the amount of resistance goes up the same each time. Also “if you have a longer piece of wire there are more atoms and electrons, which can collide to create resistance than in a shorter piece of wire, where there are less atoms and electrons”(1). This is because if you double the length of wire there would be double the amount of electrons and atoms colliding causing resistance. That is why the longer the length of Nichrome wire, the bigger the amount of resistance.

I predicted that the longer the wire the more resistance so my prediction was right and I support my theory. I also predicted that the line would be a straight line and it is, therefore my conclusion supports my prediction. I have not deducted the resistances of the leads because if I did not measure it, the graph line does not go through the origin because of this resistance being included. Where the line crosses the y-axis is the resistance of the clips and leads.

If the wires diameter is increased the resistance will decrease. This is due to the increase in space for the electrons to travel through. “Because of this increased space between the atoms, there should be fewer collision. If the cross-sectional area of the wire were greater, the resistance would be less because more current will be able to flow through the wire.”(1)

Temperature has an affect on the experiment as the resistance increases with temperature. If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance.

The type of material will affect the amount of free electrons, which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. “If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase in the number of electrons.”(1) Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.

The reason that the length is proportional to the resistance is to do with free electrons. The free electrons constantly flow around the circuit, as fast as they can. The ions in the circuit though, get in their way, and the electrons and ions collide causing resistance. This is what causes resistance. “By increasing the length of the wire, we are adding more ions to the circuit therefore increasing the chance that they will collide.”(1)

Evaluation

Method

I managed to set up the apparatus as accurately as possible. I used all the same apparatus for each experiment, I did this so that it was fair and made my results accurate.

During my experiment I have noticed several modifications I could make to improve on my investigation if I was to repeat it. The first modification I would make would be to use pointers instead of crocodile clips I would do this because pointers could be placed more accurately. I found it difficult to attach the crocodile clips onto the wire. I found this difficult because I had sellotaped the wire down to the ruler to keep it in place yet this did make making accurate measurements hard.

As well as making these modifications I would also improve my Investigation by testing the same wire but different widths of that wire. I would do this to expand on my Investigation.

My results were quite accurate apart from four, which I found, did not match. It did not match because the others went up by 0.7ohms but four is not the same because it went up by 0.6ohms or 0.8ohms. This is not really a big difference but it does mean that the experiment was not as accurate as it could have been. My anomalies could be down to many things but I think the crocodile clips might not have been put on straight instead they could have been placed on a tilt, this would mean that the distances in between the clips were incorrect.

All of the averages of the three experiment were either totally accurate or just 0.1ohm out. They were all very close which means they are accurate. The only ones that have a bigger difference of 0.2ohms between the are experiment three for the 0mm to 600mm which is 4.8ohms and the others were 4.6ohms and the experiment one for the 0mm to 900mm, which is 6.9ohms and the others are 6.7ohms. These were not anything to panic about because they averaged out correctly and gave no major anomalies. I think my results are still reliable.

To also improve on my results I would use a digital voltmeter instead of an analogue meter. I would do this because “a digital voltmeter is a lot more accurate than an analogue because if the needle in the analogue voltmeter is bent then the readings given off will be false whereas a digital voltmeter does not rely on a needle or any other manual movements” (1).

Graph

On my graph the points I have plotted are all joined apart from four. This means my line of best fit is accurate and that I have no major anomalies. Therefore my conclusion is correct because the graph should go up by almost the same each time. I spotted anomalies when I was looking at my results table because all of the resistances go up by 0.7ohms but four goes up by either 0.6ohms or 0.8ohms.

I think I got those anomalies because of a wrong measurement when I was attaching the crocodile clip to the wire. I probably just made the increasing gap bigger than it should have been because the resistance between the two points were more than normal 0.7ohms.

If I had time the additional experiments which I would have carried out to be sure of my graph results would be longer length of Nichrome wire, to see if the graph would carry on in a straight line and increase by the same resistance each time and the resistance of the clips and leads would have been less significant.

I do not think there is another way to investigate the variable I did apart from changing the apparatus and using a power pack, digital voltmeter and ammeter instead of using a multimeter.

Things, which could affect the end result of my investigation, need investigating. Things that could affect my final results would be rusty old crocodile clips so I would have to test them to make sure they gave the correct resistance. I could do this by attaching two crocodile clips together in a circuit with a multimeter and if the resistance were different from 0.3ohms I would know that they are not giving me the correct resistance. I know this because in my preliminary experiment I did the same but with clean crocodile clips and they gave me a resistance of 0.3ohms. If I were using a power pack I would also need to investigate the heating affect. I would have to use a thermometer to check the temperature of the wire.