Width is another thing which affects the resistance of a wire. If a wire has a large diameter there is plenty of room for the electrons to flow through meaning less collisions and not as much energy loss. However, in a thin wire there is not as much room therefore there are lots of collisions and a lot of energy is lost. To conclude that there would be a high resistance in the thin wire and a low resistance in the thick wire. Also with the corridor you can have the variable, changing the width of the corridor would make it easier to get through seeing as you wouldn’t bump into as many people and would be able to get to the destination a lot quicker.
To summarise that a hot, thin, long, Insulator has the highest resistance.
In this experiment I am using the length as a variable.
Resistance is the power of a substance to resist the flow of an electrical current through it. I know Ohms law V = IR. However, this it is important to remember at all times that this equation is only valid if the temperature of the room is the same (normal room temperature) for all the experiments.
I can then re-arrange this formula in order to work out the resistance when knowing the current and voltage in a circuit.
Resistance (Ω - Ohms) = Voltage (V)
Current (A or I)
From this I go on to make my prediction. I predict; ‘the longer the wire the greater the resistance’. I think this because if the wire is longer then the electrons will take a lot longer to push through all of the atoms. The relationship between the wire length and the resistance should be directly proportional. I think this because in a wire twice the length of another there would be double the amount of atoms causing the resistance.
I can now make a quantitive prediction, predicting the likely results I am going to achieve from doing this investigation. “The Phillip Haris Catalogue 2003” is where the wire was purchased to do this experiment. They say that 1 metre of the wire should have a resistance of 7.0Ω. As long as its diameter is constant, resistance in a conductor should be proportional to the length of the conductor. Knowing that 0 metres has a resistance of 0Ω I work out what the resistance should be for 0.2m, 0.4m, 0.6m and 0.8m should be.
To make sure this experiment is a fair test I will have to look at all the variables and know which ones I am going to keep constant.
I am going to keep the temperature constant – room temperature, (although it may be different when the wire is heating up from the charge). I will keep the voltage constant, 5 volts, and I will keep the thickness of the wire constant. The Length will use the Length as the variable and the resistance will change with it.
Here is a list of the apparatus I will use for my experiment:
Mains cell – power supply which consists of the constant 5 volts
2 x Crocodile Clips – needed to connect to the circuit
Ammeter – to read the current
Voltmeter – To read the voltage
Connecting wires – connecting my circuit together
Metre ruler - Measure distances of wire
Wire - To experiment with
Below is a diagram of what my circuit will look like:
To start my experiment I will get all the equipment together and create a simple circuit including the power pack, ammeter and voltmeter. I will then link these up using the wires and crocodile clips. Once I have it set up and I have a table to write the results in I am ready to go. I will turn on the power making sure it’s set to 5 volts. When I turn on the power I have to make sure that I only leave it on for a couple of seconds otherwise the heat in the wire will rise, which will make it an unfair test plus Ohms law will not work – it needs constant room temperature, as already mentioned. I am going to have to read the measurements of the meters very quickly in order to avoid this problem. I will attach the crocodile clips onto the end of each wire so I can clip them on to the wire. I will keep one clip on 0m at all times and move the other one up and down to vary the length of the wire. When taking measurements I will use the parallax method. Using this method will get you accurate results without having to use electrical or digital equipment. I will line up the pointer with the reflection in order to get an accurate reading. Preliminary work – the diameter of the wire was checked with a micrometer and found to be 0.28m along its length.
In order to make my results reliable I am going to repeat each test three times this will give me a good accurate set of results which I can compare with my predicted results. It also is a good idea to repeat the test because I may have set the experiment up wrong which would lead to an anonymous result.
I will have a range of evidence seeing as I am doing each test three times.
Once I have obtained the evidence I need I will show it in graphs and compare my results to see if they are similar to my predicted results and see if there is any anonymous results or not, and what the reason could be for these.
It is vital that I make sure this way of obtaining my results will be a safe procedure. In order to do this I will do a quick check to make sure all of the apparatus is ok, no split wires or broken crocodile clips. Another vital thing before turning on the power is to make sure all the apparatus and surface area we are using is dry. Another thing I will keep an eye on is the voltage. I want to make sure it is kept at 5 volts and it doesn’t change. I need to use the equipment in a safe manor and all times and make sure I don’t leave the power running too long.
Below is a table of my results I gained through the doing this experiment. I have worked out the resistance to two decimal places using Ohms law; Voltage divided by current equals resistance.
Looking at the table above it shows all the results I obtained through doing this investigation. The majority of the results are the same and they are more or less as I predicted. The one result that stands out to me and looks anonymous is length 0.4m, test 3 voltage – 4.1 volts, in red. This was slightly different to the other results. There is an explanation to this. It could either be I read the measurement wrong, or seeing as it was the third test it was more than likely that the wire got too hot.
I wanted to find the average for each different length of the wire because it will probably be the most accurate result. Seeing as I did each test three times to get the most accurate results I could.
As you Can see from the graph above as the length of the wire increases so does the resistance, just as I predicted. The graph shows a positive correlation although towards the end of the line you can see it goes slightly higher. I think this is because I didn’t leave quite enough time in between for the wire to cool down this means that the temperature was higher on the last tests this would then increase the resistance even more. At all times the wire needs to be at room temperature other wise Ohms law does not work and
Looking back at my results and predictions I was in fact correct in saying, ‘the longer the wire, the greater the resistance’. This is because as I already mentioned with the longer wire the electrons have further to travel and more atoms to push themselves this makes the resistance higher. Where as with the shorter wire there is less to travel and it didn’t take quite as long to get a reading of the volt and ammeter. I think i achieved some very good results and it helped by doing each test three times making them more accurate.
I didn’t find any problems setting up the equipment up and all went to plan. The tests all went well and the reliability over all was quite good. Although theee are a couple of changes i would make if i were to go through with the same experiment again. Firstly i would leave more time in between each test. This would allow time for the wire to cool down, leaving the temperature constant throughout the experiment. Looking at my graph of average results you can see that heat has affected the resistance seeing as the whole graph is a positive corelation and goes up in equal amounts up until 0.8m – 1.0m where the resistance increase because there are more atoms to pass. I would also check for the three tests that the crocodile clip is always clipped on the same length because i think that could have easily changed and i wouldn’t have noticed, seeing as i did this experiment in a bit of a hurry because there was a lot to be done. If i were to do the investigation again i would also check the room temperature and try to do each tests on the same temperature, i know it is hard to do this but i think it would be nice to see if my results would vary or not.
If i had time i would have liked to extend my investigation. I would do this by using the width of the wire as a variable. I would keep to testing three times though because that worked well, and accurate results were gained. After that i would go on to test how reistance is affected by my other theories on different variables. I have enjoyed doing this investigation and have learnt a lot and have proved my prediction.
