So we should think of a metal as consisting of ions rather than atoms. Therefore the further the current has to travel, the resistance should increase, using this theory I can predict that doubling the wire should double the resistance, again, in a fair test where the temperature does not change.
Temperature will effect my results due to when metals are heated the expand(get bigger, since heating causes vibrations in the metal, this would cause the positive ions to move around in the wire, this would cause more resistance, and therefore decreasing the temperature less resistance.
The type of wire should definitely effect my results. If I used copper wire, there would be low resistance, due to coppers lack of positive ions, in comparison to if I used lead, I would find that high resistance would be shown, as lead has many more positive ions to attract the electrons that copper does.
I will investigate the length of the wire and how that will effect the resistance of the wire constantan at 28 SWG(standard wire gauge). I will keep all the other factors measured above the same. I will repeat the experiment three times, I will measure 1m of constantan wire and record the voltage and amps, and therefore the resistance, every ten centimetres starting at 10 cm and finishing at 100 cm.
Prediction
I think that as the length of the wire increases so to will the resistance of it. I also think that the rate that resistance of the wire increases will be directly proportional to the length. With electricity, the property that changes electrical energy into heat energy, I can consider electrical current to be resistance. A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure. All metals are conductors. With electricity, the property that transforms electrical energy into heat energy, in opposing electrical current, is resistance. A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure. All metals are conductors and have an arrangement in similar form to this
As a result of the structure that can conduct(all atoms are conductive), the outer electrons can move about freely, even in a solid. When there is a p.d (potential difference) across a material that conducts, all of the free electrons arrange themselves in lines to move in the same direction. This forms an electric current. Resistance occurs when charged particles that make up the current hit other particles in the material. As the resistance of a material increases, so to does the force required to push the same amount of current. In fact resistance, in ohms(R) is equal to the electromotive force or p.d, in volts (V) divided by the current, in amperes (I) – Ohm’s law: R=V÷I.
So in conclusion I believe that the longer the wire is the greater the resistance due to the more positive ions in the wire, this will create the heat and will cause more volts to be pushed through the circuit. This will cause greater resistance. So resistance is directly proportional to length of wire, When the wires length increases so does the resistance.
Preliminary Results
I first took some preliminary results to determine what sort of results I should be achieving in the actual experiement.
Method
- I set up a series circuit containing: battery pack(set at two volts for all experiments); ammeter; voltmeter; reastat; two crocodile clips(to attach to the wire every 10 cm(this was what I am investigating).
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To keep this experiment as accurate as possible we need to make sure, firstly, that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when we do this.
- I then placed a crocodile clip at 100 cm and moved the other crocodile clip at 10 cm intervals, starting at 90 then down to 0 cm, this was to eradicate any errors in length/width of wire, I noted the current and voltage, this was averaged to form 1 result.
- I placed the current, amps and length reading on a results table.
- I used the formula R=V/I (R-Resistance, V-Voltage, I-Current). This gave me the value of resistance for the lengths. I placed this on the results table also.
I have devised a plan due to observing my preliminary results I will need quite a large range to show any significant change in resistance. This is why I will use a 90 cm range(from 10cm to 100 cm).
Diagram
Results Tables
Where the resistance values are in ohms and found using the equation Resistance=Voltage divided by Current.
Conclusion
I found that as the length of the wire increases so does the resistance. So resistance is directly proportional to length, as one increases so must the other. I can say this since the line of best fit on my graph is very straight, I have no anomalies so none of my results can be mistake. I can show how length effects resistance in a diagram:
The diagram above shows that the negative current passes through the wire.
My prediction supports my conclusion. In my conclusion I said that resistance would be directly proportional to resistance, this is true since it is backed up in my results, which I repeated three times and therefore any major and even minor errors were eradicated. This is because as the length of the wire increased the electrons that made up the current, had to travel through more of the fixed particles in the wire causing more collisions and therefore a higher resistance.
Evaluation
I believe my experiment and therefore results to be very accurate. All of my results lie close to the line of best fit, this is due to repeating the experiment 3 times, thus eradicating any anomalies. I had no anomalies. They support the definition of conclusion, my prediction that resistance is directly proportional to length.
Since all my lines lie close or on to the line of best fit some errors must of occurred- any small errors in my experiment were encountered in the measuring of the wire. This is because it is not very practical to hold a piece of wire straight, whilst holding it next to a ruler and then trying to accurately fix crocodile clips to the right part on the wire. Calculative errors would have been hard to come by since in a simple calculation errors would been made obvious. Since I had no anomalous results a) I must have had a good method b) I must of carried my method out correctly.