Method
I will measure the resistance by using the formula R=V/I. This is Ohms Law and will hopefully ensure relatively accurate results. I will have a normal circuit, but the Ammeter will be in series and the Voltmeter will be in parallel. The circuit will look as follows:
(PTO)
Safety
I must make the area safe in order to conduct the experiment safely:
- I must be sure to conduct the experiment well away from sinks, or any source of water.
- I must be sure to have dry hands whilst conducting the experiment.
- I must not use over 6V or under 10cm of wire to ensure there are no over heating problems.
Apparatus
In order to conduct my experiment properly I will need the following apparatus:
- A length of wire 1m long
- A meter rule
- 2 multi-meters
- Some leads
- Some crocodile clips
- A power pack
Fair test
In order to make this experiment fair, I will have to:
- Make sure that the piece of wire that I use is the same piece the whole way through the experiment. Also ensure that that piece of wire is made of the same metal. The reason that this is important is that, copper for example has a very low resistance compared to other metals such as nichrome.
- When a metal resists, heat is produced. Due to this the wire may expand, thus making it more difficult, or easy for the current to pass through it. It is because of this that I have decided that I will leave the wire for 2 minutes after each test to let it get back to its original temperature before starting again.
- The area of the cross-section will also affect the resistance of the wire because the wider the area, the more wire there is for the current to pass through. This is another reason why I shall need to use the same wire all the way through.
- I must also ensure that the reading on the power pack is constant, as a change in the voltage would ruin the experiment. I must also make sure that the power pack is set on DC mode, or direct current. The reason for this is that alternating current would confuse the readings on the multi-meters.
Variables
We have been instructed only to vary the length of the wire, rather than anything else. From my rough trials I have decided to keep the voltage low in order to ensure that the wire does not get damaged, thus hindering the rest of the experiment.
Results
I gathered these three sets of results; I decided to gather three sets to ensure that I have got an accurate enough average for each one.
All the calculations in the tables on the page prior to this one are given to two decimal places.
As you can see from my tables, my prediction was correct, and as the wire gets shorter, the resistance becomes less.
I will now plot graphs for the table showing averages. These graphs will hopefully provide further insight in to the experiment and its outcomes.
Conclusion
I conclude that as the length of the wire is increases, so does the resistance opposing the current flowing through the wire. I will also say that the predictions that I made were correct, and my results support that fact.
Resistance can be defined as the ease with which current passes through a substance. Electrical current is the flow of charge. In all metal conductors, current is the flow of electrons around a circuit, however in a circuit, these electrons flow in an opposing direction to that of the “conventional current.”
As I mentioned in my prediction, in a substance, there is a constant vibration of all the atoms inside. The more of these vibrations there are, the more difficult it is for electrons to pass through it. From background knowledge that I have, I know that as a current is passed through a substance, particularly metal, it heats up. The increased vibrating of atoms causes this heating up, and thus, also causes more resistance in the wire. Hence from this I have drawn that the greater the number of vibrations in a substance, the greater the resistance.
Graph 1 shows quite clearly that as the length of the wire increases, so to does the resistance, and these outcomes are proportional to each other, whilst showing a positive correlation.
Evaluation
From the evidence that I have gathered throughout this experiment, I am able to conclude that there is definitely a positive correlation between the length of the wire and the resistance that that wire has. I collected a sufficient amount of information and results to ensure that my final average of results was accurate. I did not have any extremely anomalous results. My investigation, can however be found inadequate in some areas. This is due to a variety of things: I left a 2-minute gap between each experiment, in order to let the wire cool down before the next experiment, however, I neglected to compensate for the fact that as the resistance of the wire got higher, so to did the heat of the wire, which in turn meant that I needed to allow the wire more time in which to cool down. In order to rectify this mistake, I would need to measure the temperature of the wire before the experiment, and then ensure that I allow it to return to that temperature before each new test. There is however a disadvantage to this, as it wastes valuable time waiting for the wire to cool, and our time was limited. I could extend my work further by investigating other factors that would affect the resistance of a piece of wire, such as it cross-sectional area, and I could also experiment with different types of metals. It would be interesting to compare these results with those from a metal such as nichrome, which has a very high resistance. I could also use the notion of particle vibration in my other two investigations, which would give me a definite answer as to weather my theory about particle vibration is correct.
