investigating resistance of a wire

Prediction

I predict that as the length of the wire increases so will the resistance. I think this will be quantitative and as the length of the wire doubles so will the resistance as there will be twice as many collisions and therefore twice as much resistance. I expect this to work the other way too. If there is half the length of the wire there will be only half the amount of resistance as there will be much less electrons and atoms so much less collision.

        I also feel that the thicker the wire is (the lower the SWG) the greater the level of resistance as all in all the wire will have a greater surface area and once again that will mean there will be more collision. However I do not think this will be quantitative.

        As for which type of wire will have the greatest resistance, I am not able to predict this as I have no great deal of knowledge on either metal. However in my conclusion I will attempt to look into why my outcome has occurred.

        

Apparatus List

Here is a list of the apparatus I will be using, at the bottom of the page is a scientific drawing of all the equipment that there would be a use of drawing.

• A power supply (In my case a battery cell)
• An ammeter
• A voltmeter
• A wooden board
• Two crocodile clips with joining wires
• A Constantan wire with a SWG of 24
• A Constantan wire with a SWG of 30
• A Nichrome wire with a SWG of 24

Safety and Fair Tests

To make sure there are no unnecessary risks in my experiment I have devised several basic rules which I must follow to ensure the safety of me and everyone around me when I am doing the tests.

1. I will handle the power supply carefully and only when I need to.
2. I will only use a low voltage so that the wire does not overheat or even burn
3. I will e careful when I need to handle the wire as it may be hot, although if my preliminary test was a success this should not be a problem.
4. I will use a minimum thickness of 30SWG for my wires else if they are any thinner there is a chance they will melt

To make sure that my test is not biased in any way I will

• Keep the power supply the same
• Keep using the same equipment throughout the test
• Keep the surrounding temperature as constant as possible.

I have kept all these factors the same as if I use a different power supply or different equipment they may be slightly out. Although there is a risk with any equipment I use that it may not be accurate, if I use the same equipment and power supply during all the tests then a pattern should still emerge.

I am also going to

• Ensure that I have accurately measured the length of all my wires.

I will fasten the metre stick to my board with sticky tape so that the metre stick will not move and make my 5cm differences bigger or smaller.

Method

I set up my circuit as shown at the bottom of the page and made a table to record my results in. I looked at my metre ruler to find the 40cm length of the wire and I recorded the voltage and current of Wire A. Then I moved the crocodile clips 5cm down the wire and took yet another recording. I continued along my wire taking readings every 5cm along the wire up to 90cm

After I had finished Wire A I moved onto Wire B and then Wire C, being careful to make sure my meter ruler had not slipped out of place.

        

To make sure that make sure that my results are as reliable as possible I then repeated the readings for all three wires  another two times.

Information

I have used several sources of information to help me plan and predict my test.

First and foremost I got the majority of my information from the work I did in class and homework’s.

I also used several sources of the Internet, for other help, I searched on  for ‘GCSE resistance’ and I found the website

This website gave me a great deal of help in deciding which key factors I wanted to investigate, and in realising that I could not use a smaller SWG than 30 or my wire would melt.

Obviously in using this website it has affected my planning as it limited me in the thickness of my wires and it led me to choose which factors I was going to investigate which clearly set out the path for my entire investigation.

My results.

Wire A is my Constantan wire with a SWG of 24

Wire B is my Constantan wire with a SWG of 30

Wire C is my Nichrome wire with a SWG of 30

Pattern in my results.

From looking at my results I have noticed that as the length of the wire increases so does the resistance and it is quantitative. As the length of the wire doubles so does the resistance. However I can only prove this happened on two of my calculations, as only 40 and 45 doubled (80 and 90) are still in my range. Obviously they did not double exactly, but they did up to the decimal place.  This happened on all three of my wires. Another pattern is that my Nichrome wire had much higher resistance than the two constantan wires.

Conclusion

I have discovered that the resistance of a wire is dependant on the length of it like I had predicted. I also found that the Nichrome wire is a lot more resistant than the Constantan, I will attempt to explain why later on in my conclusion.

        The one thing I have found that does not influence resistance by any great amount, is the thickness/SWG of the wires. I have compared the results of both my constantan wires and the results are never different by anything more than 0.5

        I think the reason that Nichrome is more resistant than Constantan is because it has more atoms that Constantan so there will be more room for resistance to occur.

 

Evaluation

I do not seem to have any odd results in my table or graph for my constantan wires (A and B) as you can see my results follow a smooth line of increase. However on wire C (my nichrome wire) there were two results, at 55cm and 70cm which did not follow the line of best fit.

        I do not know why these results occurred, as I can not make any connection between 55cm and 70cm, I only have to assume that seeing as the results were not way out from the trend, that I experienced a problem either with the equipment or I recorded the information wrong.

        To improve my experiment there were several things I could have done. First of all I would next time use two Nichrome wires and use a different range so that I know for sure that the results are quantitative. I would also have the metre stick below the wooden board so that my results were more accurate, although I think they are pretty accurate anyway.  

        I managed to make a firm conclusion based on my results as they were pretty reliable and not to extreme. However I feel I should have used different wires to Constantan and Nichrome as I am not very familiar with the properties so I could not make a very clear prediction or conclusion.