When a voltage, or electric potential, is applied to opposite ends of a circuit, it causes current to flow through the circuit. As the current flows, it encounters a certain amount of resistance from the conductor and any resistors in the circuit. Each material has a characteristic resistance. For example, wood is a bad conductor because it offers high resistance to the current; copper is a better conductor because it offers less resistance. In any electric circuit, the current in the entire circuit is equal to the voltage across that circuit divided by the resistance of the circuit. Resistors are often made to have a specific value of resistance so that the characteristics of the circuit can be accurately calculated.
Preliminary work.
When length of the wire is more, it's like a long line of people standing trying to stop a person running through them. The more it is, the harder it is for the person to run through them.
If the temperature increases, the wire gets hot and this also adds to resistance. This is because in heat, the particles of wire start to move about and this makes the movement of electrons through them difficult.
Material is very important, some are better. The best conductor is silver but the least reactive is gold. Reactivity is more important in long time so gold is more used in important systems. Copper is the material which is widely used because it is both a good conductor and does not react easily.
When thickness increases, the current increases as well; as a result of resistance going down. This is because there's more space available for electrons; so they would be able to flow more easily.
I started my experiment by choosing which material I will use. I chose all 4 available materials and measured the current flow. I used the same voltage (0.5 V) during the preliminary experiment. But to check how resistance would be affected I used different thicknesses 28 and 32.
Materials (thickness 28)
Materials (thickness 32)
Later on I selected copper and nichrome to work out which of them would be useful to find suitable material. Because copper had the highest current and lowest resistance, but nichrome had the lowest current and the highest resistance. Both materials I choose with same thickness 32 and voltage was 0.5 V.
Length of copper (thickness 32)
Length of nichrome (thickness 32)
From my preliminary results I can see that copper is good conductor of electricity and huge amount of current are passing through. Also resistance was extremely low, because a lot of current was passing. On the other hand nichrome is bad conductor of electricity and current is really small. Therefore resistance is high. In my real experiment I decided to use nichrome instead of copper because I want to keep current low and have high resistance to make the graph look better.
Aim.
In this experiment, I want to examine the effects of different lengths of the wire on the current, to examine how much the resistance is changed when we increase or decrease the length.
Method.
I started my experiment by building the circuit:
I had to cut the nichrome wires different length from 10 cm to 80 cm. I took current readings from the ammeter. I used constant voltage 1 V in the first result table and 2 V in the second result table. During the experiment I measured current twice for each length of wire. That was necessary to get the most accurate results.
Safety.
In my experiment some safety precaution were needed. First of all during the experiment I had to use heat proof mat, because other wise metallic wire would get to hot and burn the table. Secondly I have to wear goggles during the procedure, to protect my eyes from dangerous fire sparks. Thirdly I need to wear lab coat to prevent my skin burning from hot metallic wire.
Fair test.
To make sure I did a fair test, I kept everything constant except the length of wire. The range of length of the wire was every 10cm up to 80 cm as you can see from the table. Temperature was kept constant by waiting for the wire to become cool again; (voltage was kept constant as well at a value of 1 volt in the first results table and 2 volts in the second results table). The measurements of current were taken twice and they were similar to each other. That proves that it was fir test.
As you can realize from the drawing of the circuit up there, we used the voltmeter to have an eye on our voltage and to alter the ammeter to know the current for the different lengths. Heat proof mat was placed under the wire because in the short lengths there was risk of wire being burnt.
Apparatus list.
I used following apparatus:
Nichrome (an alloy of Nickel and chrome) wire thickness 32
Ruler
Ammeter
Voltmeter
Connecting wires
Crocodiles clip
Power pack
Heat proof mat [for safety]
Prediction.
I predict that if length of the wire gets bigger the current decreases and the resistance increases.
Results.
The following is the table of my results.
I measured length of nichrome (thickness 32) in both results tables.
Analysis.
What we can see from this table and the graph of the results [ attached in the end of course work ], is that as the length of wire increases, the current decreases, or the other way round, if we decrease the length, the current goes high. This matches our predictions. Also, there are the resistance graphs I got from our results; it shows that as the length of the wire increases, the resistance increases as well, this also matches our predictions. Both of my graphs are straight lines and also from the direction of the straight line I can see that length of the wire is proportional to the resistance. The graphs look nearly the same and it shows that if the voltage increases (in the 1st graph voltage is 1 V and in the 2nd graph voltage is 2 V) the current proportionally increases.
Evaluation.
My results were satisfactory and results are quite accurate. One of the most important things was to maintain the normal resistance of the wire, because when the wire gets hot, its resistance goes up and eventually the current decreases. This would have affects on our next results. Therefore I waited a little while before I toke the next result.
To find out whether my prediction is correct or not I would have to get more results. I need to measure bigger range for the length of wire, because it will give me clearer and more acceptable results.
Our data is accurate and supports our conclusion, for instance, the duplicate results (for test1 and test2) are very close.
The method was of my experiment was simple and to improve my method I can do the following things. We could get more trusted results if we had used a better wire that would not get hot fast or become burned; such a wire won't affect our fair test because of it's getting hot or etc due to it's low quality. The noting of the current would be much more accurate if there would be some kind of memory in the ammeter, to save the results itself without us needing to keep an eye on it every time which causes small mistakes, data logging equipment in this case can be very useful.
Considering that we only had the very basic equipment to carry out this experiment, it was not bad. However it could have been better if I would have used a more accurate way to measure the length of the wire and a constant account of the temperature of the wire would help as well. This would help me to see when the temperature of the wire is back to normal again.
For this purpose I should have used a computer which detects the temperature of the wire and if the wire would get hot computer would show it.
I really liked this experiment.
The results are acceptable, there are almost no faults, we tried to measure everything accurate and it worked. One of the main things we took into view was to maintain the normal resistance of the wire, because when the wire gets hot, its resistivity goes high and eventually the current decreases which would affect our next results. So we waited each time for the wire too cool down.
The range is acceptable for an experiment like this, although it would be better if we would also measure bigger range for the length of wire. It would give us a clearer and more acceptable view showing whether our predictions are always correct or not.
Our data is accurate and supports our conclusion, for instance, the duplicate results (for test1 and test2) are very close.
The method of course, was an amateur one. There can me many improvements. We could get more trusted results if we had used a better wire that would not get hot fast or become burned; such a wire won't affect our fair test because of it's getting hot or etc due to it's low quality. The noting of the current would be much more accurate if there would be some kind of memory in the ammeter, to save the results itself without us needing to keep an eye on it every time which causes small mistakes, data logging equipment in this case can be very useful.
Considering that we only had the very basic equipment to carry out this experiment, it was not bad. However it could have been better if I would have used a more accurate way to measure the length of the wire and a constant account of the temperature of the wire would help as well. This would help me to see when the temperature of the wire is back to normal again.
For this purpose I should have used a computer which detects the temperature of the wire and if the wire would get hot computer would show it.
References from: Encarta Reference Library 2002