SAFETY
Safety is an important factor in this test in that if used in the incorrect way then electricity can kill. SO:
- I will not touch sockets and the power supply unit (PSU) with wet hands.
- I will use a low voltage – too high a voltage will melt the wire and damage equipment.
FAIR TEST
To make the test fair I will only change one variable, that being the length of the wire. I will use the same length of wire each time and same components. I am going to put the PSU on 6 volts – a safe voltage, relating to safety, from preliminary, 8 volts was too high and began to melt the wire on some tests and will use 0.25mm nichrome wire. I have a range of 10 measurements – from 10cm to 100cm at regular 10cm intervals, 10 is an easy number to take averages with and will give me enough data to obtain a fairly accurate result; I will test each length of wire 3 times and take an average.
EQUIPMENT & DIAGRAM
CHANGES FROM TRIAL EXPERIMENT
While trialling the experiment I felt that the following changes needed to be made:
-
Measure at 10 regular intervals instead of the original 5 – it will ensure that I will get a better average.
- Use sellotape to stick wire to ruler – stop wire become twisted and keep it straight on the ruler.
- For the shorter lengths of wire, the power pack must only be on for a matter of seconds, due to the lack of wire needing to get through, the particles will build up and melt the wire.
METHOD
- Measure a piece of 0.25mm nichrome wire to 100cm
- Connect all components together using crocodile clips
- Attach the wire to the ruler, using Sellotape.
- Switch the power unit onto 6 volts and onto a direct current, I only want the current to be flowing one way and not alternating.
- Measure 10cm on the ruler, turn the P.S.U. on and take the reading on the ammeter and voltmeter. I will do the same for 20cm, 30cm, 40cm etc. Before repeating the process again, twice for all 10 measurements.
-
Use the formula, RESISTANCE = VOLTAGE
CURRENT
to find the resistance for each measurement before taking an
average of the 3 resistances.
GRAPH
ANALYSIS
From my graph and table of results I feel that my results were relatively accurate.
Having looked at my graph, I can say that the wire if 100cm, the resistance was greatest, this is exactly what I said in my prediction. Therefore, I can say that the more wire there is, the more resistance there is. I think that the wire measuring 100cm had the greatest resistance because of a number of factors:
- When the wire increased in length, the more current was required, therefore decreasing the current speed and increasing the resistance.
- When electrons were in the circuit, they were forever losing energy. While going through a longer wire and longer circuit then the electrons will lose energy and more will have to be sent, creating yet more resistance.
As you can see, there are a couple of points that prevent the graph being a smooth line, notably, at 30cm and 60cm. The reason of this could be due to the wire not being measured out properly or possibly by misreading the ammeter and voltmeter.
My prediction was therefore correct, saying that the longest wire would have the greatest resistance.
EVALUATION
In conclusion to the investigation, I can say that, in my opinion I had insufficient data in order to analyse and get an accurate graph towards my aim. If I tested again, I would maybe do 25 tests instead of 3, giving me an accurate answer and hopefully a more exact straight line on my graph.
My results may also have been inaccurate due to the possible misreading of the ammeter and voltmeter, at the shorter lengths of wire we needed to switch the circuit on and off very quickly – to prevent the wire from melting.
If I did the investigation again, I wouldn’t be able to use a resistor, which would defeat the point of the experiment. I’m not sure how I’d tackle this problem. I could also have used a digital voltmeter instead of an analogue one because the analogue one would be a lot less accurate than a digital one. I feel the analogue one is less accurate because I would have had to read the meter manually with my whereas a digital one would have given a much more detailed reading. I could also change a variable, which would see the problem from a different perspective; I could look at the thickness of the wire or the voltage at which the power pack is set. This would give me more data to work with, on top of the set of results in this experiment.
In conclusion, I feel this experiment was quite successful although more tests mean a more accurate result.
