Method
First I will connect the circuit as shown in the diagram below, remembering that the voltmeter should be connected last. I will also make sure that the ammeter and voltmeter works properly. If the readings on the meters are shown by having a minus sign, then I will have to switch the wires on the voltmeter around. I will then take the remaining wires and connect them to the power supply. Then I will get a piece of wire, measure it to 30cm in length and then connect two crocodile clips to either side. I will then take the reading for the volts and amps. I will then switch off the power supply and wait 5 seconds before turning it on again. Then I will take the next reading. I will do this for the other 4 wires and repeat each wire 3 times. This would give me accurate results. Then I will work out the average of each wire for volts and amps. To do this I will add the 3 readings for each wire and divide it by 3. After I will find the resistance for each wire, by dividing the volts by the amps.
Variables:
In this investigation, many variables can be used and changed. These variables are the way to achieve different observations. Here are most of the variables that would affect my findings:
- The material the wire is made from is one of the most important variables in this investigation. A suitable material must be chosen to achieve accurate results. As most metals conduct electricity differently I have to choose a wire that will give the most precise results.
- The amount of current in the circuit is just as important as the amount of potential difference. If the current was made larger and the potential difference was kept the same then the resistance should be lower. If the current was made smaller and the potential difference was kept the same, the resistance would become larger; therefore the amount of current used should stay the same throughout the investigation.
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The length of the wire can drastically affect my results for instance, If there were two wires, one longer then the other, then the longer wire should still have the same amount of current flowing through it, but more wire to cover. So the longer wire would have more resistance. Therefore the length of the wire should stay the same during each individual investigation.
- The diameter of the wire can drastically affect my results for instance, if there were two wires. One wider then the other, then the wider wire should still have the same amount of current flowing through it but more wire to cover. So the wider wire would have more resistance. Therefore the diameter of the wire should stay the same during each individual investigation.
- The affect of heat on a wire is another variable that may affect my investigation. Although this is a minor variable, it is still quite important. For example the resistance will increase if the temperature rises. Therefore the temperature should stay constant throughout my investigation.
Fair testing:
In order to keep this investigation to run fairly and accurately you would make sure the following things are taken in concern:
- The ammeter should stay on the same setting throughout the investigation and the same ammeter should be used, because different ammeters give different readings.
- Also the voltmeter should stay on the same setting throughout the investigation and the same voltmeter should be used because different voltmeters give different readings.
- When the power pack is being used, the same amount of voltage must be used each time. As different amounts of voltage will give different results.
- When the wire is attached to the ruler there should not be any tangles in the wire. As this will affect the length of the wire. This would make the potential difference larger then it should be and this would result to a larger resistance.
- The crocodile clips must also be put down on the correct number because a 1cm difference could mean quite a bit to the end result.
Safety:
When dealing with electricity everything must be carried out properly and risks cannot be taken. Water should never be put on electric components unless they are specifically made so that they can go in water. The power pack unit should never be turned to maximum power unless the component can take it. Otherwise it could result in the component exploding.
Equipment:
Evaluating and Analysing
Analysing
As you can see from the graph, it has proved my prediction which states the thicker the wire the lower the resistance and the thinner the wire, the higher the resistance. You can see this from my prediction as it shows that wire 4 – 0.19mm wide had a resistance of 5.74 ohms whereas wire 1 – 0.56mm wide had a resistance of 0.61 ohms. I can also conclude that, as the cross-sectional area of the wire doubles; the resistance halves (provided the length of the wire stays constant). The only trend on the graph is that the thicker the wire gets the smaller the resistance and that the thinner the wire gets the larger the resistance. You can see this from the curve which is produced by plotting the points.
Evaluation
I think that I carried out the method accurately so I got accurate results. I think that three repeats were sufficient. I feel that there were a few inaccurate results but not inaccurate enough to call an anomaly. The method was quite accurate but I felt that some of the wires were too thick and short and thin and long so the readings on the ammeter and voltmeter where not what they where meant to be. Some of the wires may have had different resistances, which may have affected the results. The results of this experiment would be difficult to improve on because they are reasonably accurate, and there were no anomalous results. If I were to do this experiment again I would take a much wider range of readings and more readings so that a more accurate average can be taken. I would also take the reading from the ammeter more than once so I could get an average. This would make the experiment more accurate. I would also use a longer length of wire. I could have also used a higher voltage and used a thicker longer wire. The clips could be attached more carefully, and a more accurate ammeter could have been used to make sure that the current is always exactly the same. Also a better voltmeter would have given better resistance results. The wires and clips used would also have an effect on the resistance and the wires could be insulated better to reduce heat loss. To be more accurate with my results I would place the meter rule directly under the wire, so therefore it would be measured easier and therefore making the lengths more precise. Instead of connecting the voltmeter to the main circuit, I would connect it to the wire that is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well.
