As the title suggests, what I intend to do in this experiment is find out what factors will affect the resistance of a wire. For example, if the length of a wire is shortened, then will the resistance increase or decrease. Fair test: In order to make this experiment a fair test, to obtain reasonable results, only one thing can be changed. All the other factors/variables would have to remain exactly the same. For example, if the length of the wire were being decreased at a reasonable measurement range then that would be the only thing that should be changed.
The type and thickness and voltage should not changed, otherwise that could affect the results obtained. Safety As in every scientific experiment, safety precautions must be followed. The safety measures to be taken here are as follows:
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Remember to keep voltage the same throughout the experiment to make it a fair test. Prediction: I predict that as the length of the wire decreases, the resistance will decrease. Therefore as the wire length increases, the opposite will happen and the resistance will increase because the resistance has more atoms to collide with. The reason I predict this is because long wires have more friction, resistance is increased; the less the current will flow. If the thickness of the wire is changed, then I predict that the thicker the wire, then the resistance will decrease and the thinner the wire then the higher the resistance will be.
The reason being that thick wires have more space for the resistance to pass through; more current can flow through because it is a better conductor. Measurements: The ranges of measurements I will be using in this investigation are as follows: The length of the wire will be shortened every 10cm. The reason being that I can get enough readings to plot the graph and the results should be close enough to compare to one another. When I test the different thickness, I will be testing each of them at 1 meter. N. B: When the wire reaches a length or 30cm or below, the wire could overheat and jump off the readings, causing some peculiar results.
Ohm’s Law: The ohm’s law tells us that ‘The resistance of a wire is the same, whatever current is flowing through it, provided that the temperature remains constant. ‘ Ohm’s law was worked out by George Ohm, a German scientist, who said that Resistance = Voltage divided by current. So Ohm’s law gives us a way of working out the relationship between Voltage and current, and the concept of resistance. Ohm’s also showed the resistance on a current- voltage graph, to show how the current affects the voltage produced over a component. Usually the horizontal axis of the graph is the current and the vertical axis is the voltage.
For a particular current, you should be able to read what voltage should be produced. Also, if you know what voltage was applied to a component, it will tell you what current will pass through it. The gradient of a current- voltage graph can tell the resistance of the component. If the graph is a straight line, then the resistance is the same for any current. A straight line has a constant gradient. If the graph is curved, then the resistance changes depending on current is being used. If the gradient gets steeper, with more current, then the resistance has also increased. (Reference- science encyclopaedia).
As the above results tables show, as the wire decreases in length the resistance decreases too and the longer the wire, the longer the wire, the lower the resistance. Therefore my prediction was correct. The reason the resistance is lower is because it has less space to move through when the wire is shortened. The resistance was calculated by dividing the voltage by the current. The table shows the various lengths of the same wire (34 constantan) and their resistance.
If observed carefully, you will find that there is not much difference between each one. The difference, ranges from 0. 5 to 1. 5. Therefore as you will see in the graph, the resistance is constant. In order to obtain accurate results, as a group, we used a digital ammeter to measure the current. The current is more or less constant, however when the wire reaches to the length of 30cm and below, the readings jump off the scale. This could be because the wire has overheated and therefore the peculiar readings. For example, when the length was 20cm the ammeter reading was 2.
6 A when the previous reading (30cm) was 1. 075. That is a huge jump compared to the differences between the other readings. Table three shows the results of the different thickness of wire. 26, which is the thickest wire has the lowest resistance and 32, which is the thinnest wire, has the highest resistance, just as my prediction suggests. The results do seem accurate, however at first I did think that the reading of the 32 constantan copper wire was a bit high. Then I remembered an important fact about copper. It is an extremely good conductor, which is why when experimenting the wire got hot very quickly.
ANALYSING From this experiment I have found out that there are different factors that affect the resistance of a wire. The factors that I have investigated are the length and thickness of a wire. In the experiment, as the wire got shorter, the resistance decreased, and if the wire were increased then the resistance would increase too. If the thickness of a wire were to be changed then the thicker the wire, the less resistance and the thinner the wire the more resistance it will have. I have also found out that the resistance is calculated by dividing the voltage by the current.
This calculation was used in my experiment and showed that the resistance is roughly constant. If some odd results were obtained, it was because at a low voltage the power packs are inaccurate and at a high current, we might gain a heating effect. Ohm’s law can be proved by the graph due to the fact that the graph has a straight line; therefore it has a constant gradient, meaning a constant resistance whatever current is passing through it, providing the temperature is constant. If the graph were a curved, then that would mean that the resistance was changing.
If that were the case the resistance could be found for any point by taking the pair of values (V, I) from the graph and sticking them in the formula R= V/I. (Information obtained from physics revision guide. ) That would be disobeying Ohm’s law. In my opinion, the resistance of the 32- copper wire seemed odd since the thinnest wire is supposed to have the highest resistance. However a good conductor, which is what copper is, will allow current to flow through it easily. Therefore that’s why the ammeter reading for the copper wire, which measures the current, was very high, compared to the reading of the other types of wire.
A nichrome wire would have more resistance than a copper wire of the same size, because less current flows through it, making it not such a good conductor. We can also conclude that the thickest wire, type 26, had the highest resistance because less current could flow through it. EVALUATING: This investigation was conducted following the method above. By following those steps, I managed to obtain more than enough readings to plot a graph with and I managed to obtain accurate results, until the wire reached 30cm (TABLE 1). However my previous readings were fairly accurate, which were more enough for me to plot a graph with.
I had seven readings when only 6 are needed to plot a graph. The results of the first experiment my group conducted, (TABLE 2) were much more accurate than the second one (TABLE 1). The resistance was very constant, however we did not complete the experiment. We planned to carry it on the next lesson, but it would not have been a fair test because we used a different power pack and the voltage was not the same. We found out that we were getting odd results to our previous ones; therefore we had to start the whole thing again.
We made sure we finished that experiment and even had time to conduct another: an investigation to find out whether the thickness of a wire would affect the resistance. Since I only had to investigate five different wires, obtaining five results, this investigation was easier to conduct because there were fewer to do and I knew exactly what I was doing. It took me less time to set up the circuit and it was definitely a fair test. However when it came to the 32-copper wire the resistance was very high. I expected it to be high because it was one of the thinnest wires, however not that high.
I suspect I either recorded the wrong reading or because at low voltage the power pack was inaccurate and at high current there was a heating effect. However, as I mentioned in the analysing section, there was a simpler explanation. From previous work, I remembered copper is a very good conductor, therefore the high current reading. In future if I conduct another similar experiment to this one there are some improvements that could be made: I could compare my results with other people to see if they got the same or near enough results.
That way I would know whether I was on the right tracks. If I am stuck on connecting the circuit, I could draw a diagram first and follow that. I should finish every experiment the same day; so that I get more accurate results and can compare the results to the results of another experiment, on the same subject and would not have waste time having to start the same experiment again. I could have done some further research and find out what and if there are any other factors that affect the resistance of a wire and then I could have conducted an experiment.