Electricity and Magnetism - Sample Essay
Factors/Fair test For working out the resistance due to with the factors that may cause a change in the resistance or, the gauge of the wire, at what length we measure the resistance form and also the temperate at what the wire is at. To keep this test fair the only variable that we will change is the gauge of the wire, as this is the thing that we are trying to find out about, we will not change the length as we know that resistance changes with length, so we must keep the length the same for all the tests on thickness.
We also need to try to keep the temperature the same as this also affect the resistance, however this will be a bit tricky as when you run a current through a wire the wire heat up, therefore we will have to run the current for a very short amount of time so the wire does not heat. For the length the factors that may affect the resistance are the length of the wire, the thickness and the heat. To keep this a fair test we will only change the length of the wire, we will keep the gauge the same as the thickness affects the resistance of the wire.
We will also keep the temperature the same however again the temperatures will he harder to control. For working out resistance due to temperature the factors the will affect the resistance are the temperature, the thickness of wire and the length of the wire. To keep this a fair test we will only change the temperature, we will keep the length and thickness the same as these both affect the resistance. A factor that affects all of this is what type of wire we use, as Nicrome has a much greater resistance than silver. For all of the tests we will use Nichrome as it will be affected more by the variables.
Prediction I predicted that as the length of the wire increases the resistance would increase, this is because electrons have to travel further. This is because inside the conductor the battery sets up and electric field (E) and E=Voltage/Distance. So if the wire is longer the electric field is weaker if the voltage stays the same. The field will put a force on the electrons and accelerate them. So if the wire is longer, the field is weaker, there is less force on the electrons and the flow of current is less. This means resistance in greater.
As well as this I think that if we increased the temperature of the wire, that this would increase its resistance because as anything gets hotter the atoms inside would have more kinetic energy. Therefore as a wire increases in temperature the structure of it becomes more chaotic meaning that the transfer of electrons more difficult, increasing resistance. if the atoms are moving faster the atomic separation can change so instead of electrons been close there further apart, meaning again that the transfer of electrons is harder, meaning the resistance is harder.
Also I predicted that if we increased the thickness of the wire then the resistance would decrease. This is because if the wire is thicker there are more atoms at a cross section of the wire. This means that there are more atoms for an electron to ‘jump’ to. So if the cross section is bigger then there are more electrons at any given cross section. This in turn means that if there is a higher current in the thicker wire, the higher current means a lower resistance. Apparatus We used a lot of apparatus for measuring the resistance for length and width, these include:
1. Power Pack 2. Wires 3. Length of wire with different gauges 4. A voltmeter 5. Ammeter For measuring the temperature we needed: 1. Bunsen Burner 2. Heat Proof mat 3. Wires 4. Thermometer 5. Clamp Stand 6. Clamp (2) I took this photo during after the experiment 1. Tripod 2. Sand Tray 3. Coiled Wire 4. Wire Cutters My Experiment At the start of our experiment we started with preliminary work, this consisted of us investigating what would be best for our main body of experiments on resistance due to the temperature of the wire.
At first we tried using a wire that was coated in a protective vanish so it wouldn’t matter if they touched. However this wire didn’t have high resistance. We submerged the wire in distilled water so the water would not act as a conductor. Although when we did the experiment we found that the wire had little resistance that an increase in temperature by 80a?? c, the resistance did not increase or decrease substantially. Next we did the same experiment with Nichrome, a higher resistance wire, however this had no protective vanish, meaning that we to take care not to allow the wire to touch.
We repeated the experiment and this time we had a more resistant wire, we found that as we got close to 100a?? c the resistance increased, this mean that when we did this experiment for real we knew we would have to find an alternative way of acquiring higher temperatures because we needed higher temperatures. Then we decided on using sand tray to heat the wire in, this is because they will heat to higher temperatures, this is because it allowed us to heat it to hotter than a Bunsen flame without evaporating. We also knew to start the experiment at 100a??c as that was where the resistance started to increase. -Investigation For the investigation for length and width, we used a 28, 36 gauge.
We started with the 28 gauge and I measured the resistance from 40 to 160cm (every 10 cm). I repeated the experiment twice so we could eliminate any outliers, also this would allow us to work out a mean, and add range bars to our graphs. We then did the same for the 36 gauge, as well as repeating it twice. Then we worked out the resistance by using R=V/I, and the average of these results.
We then used these results for a scatter graph, drawing a line of best fit showing marked outliers, and added range bars every 20cm. For the temperature investigation we used a coil of wire, this was made from Nicrome. This is because it has a high resistance. Then we buried the wire in the sand tray so the hot sand would encase the wire, allowing the wire to be heated. We then connected the coil to a Micro-ammeter than we set to show the resistance, not amps. After this we heated the sand with 2 Bunsen burners to 100a?? c, as one did not heat it quickly enough.