Resistance investigation - Sample Essay
When cooled to extremely low temperatures, some conductors have zero resistance. Currents continue to flow in these substances, called superconductors, after removal of the applied electromotive force. The reason that the length is proportional to the resistance is to do with free electrons. The free electrons constantly flow around the circuit, as fast as they can. The ions in the circuit though, get in their way, and the electrons and ions collide causing resistance. This is what causes resistance. By increasing the length of the wire, we are adding more ions to the circuit therefore increasing the chance that they will collide.
Analysis and relation to preliminary experiment According to my research, the resistance of a wire generally increases as the temperature of the wire increases. This means that if the heat of the wire does increase, than the results we be inaccurate and therefore the experiment will have to be repeated. That is why it is essential to keep the wire at a constant. It also tells us that the resistance of a wire is directly proportional to its length and that the resistance depends on the material of the conductor.
That is why it is we are going to repeat the experiment – to see which reading was most accurate to my scientific prediction. To decrease the chances of getting anomalous results I am going to use a micrometer screw gauge, to work out an accurate measurement of the constantan’s thickness. The micrometer screw gauge. The method of measurement is: 1. Work out the value of a division on the spindle scale. 2. Using the ratchet, close the jaws of the instrument full. The zero on the spindle scale should coincide with the horizontal reference line. If not, note the zone error. 3.
Using the ratchet, close the jaws on the object to be measured until it is gripped. 4. Note the reading of the highest visible mark on the sleeve (in this case 6. 5mm). 5. Note the division on the spindle scale, which coincides with the horizontal reference line (in this case 0. 41). 6. Add the two readings and add or subtract the zero error to get the correct reading (in this case 6. 91). All experimental measurements are subject to some errors, other than those caused by carelessness (like misreading the scale). The most common errors, which occur, are parallax errors, zero error and reading errors.
When starting a reading, therefore, a number of significant figures should be quoted which give an estimate of the accuracy of the readings. I will take 10 readings, and I will repeat the experiment 3 times giving me a range of results, I will investigate the length starting with 20cm and increase by 20cm and finally finishing with 200cm. I will then compare the 3 results against on another, and this will help us see any anomalous readings. Hopefully, I shall find that the difference between the first and last readings should be proportional according, to my scientific knowledge.
I am going to plot 2 graphs and I will pick the best results and plot that on graph paper, then I am going to work out the average resistance of the three results and plot that on another sheet of graph paper. I am not plotting it on computer because it would be harder to draw the line of best fit and explain anomalous results. Main experiment So, I can now move on to the actual experiment, I am going to use the same apparatus I used in the preliminary experiment, which are: Electric Wires 2 Crocodile clips Metallic conductive wire: constantan (cut at 200 cm) 1 Voltmeter 1 Ammeter 1 Power pack 2 metre rulers.
Cello tape and a Micrometer screw gauge. But this time, I am going to measure the thickness of the wire at 10 places on the wire, using the micrometer screw gauge. I used wire A, a constantan wire of approximately 0. 3mm in diameter. I suggested that we do it at every 20 centimetres. I used the method on page 11 and the readings I got were as below: Length of wire (Cm) Measurement (mm) The Method First, I had to get the apparatus. I then placed the equipment on a dry surface, as we were using electricity.
I set up the apparatus in the same way set in the preliminary experiment, (In series) as below: I then made sure that the voltage was set to 4 volts. I took account of the safety regulations and I started the experiment. I started to measure at 20 cm, and increased by 20cm after each reading until I got 10 readings, from 20 cm to 200cm. Then, I repeated this experiment 2 more times I recorded all my readings on a table. Obtaining Evidence/Results The results I found were as below: Experiment 1 Length (Cm) Thickness of wire (mm) Voltage (V) Current (C) Resistance (? )
Experiment 2 Length (Cm) Thickness of wire (mm) Voltage (V) Current (C) Resistance (? ) 2Experiment 3 Length (Cm) Thickness of wire (mm) Voltage (V) Current (C)Resistance (? ) I used the formula: Resistance = P. D across the wire (V) Current through the wire (A) Where in symbol form it is: R = V I Where R is resistance, V is voltage and I is current. Seeing that I have finished the experiment, I have to move on to plotting the graphs, but first I have to work out the average resistance of the three results tables on page 14.
All readings are accurate to 3 significant figures. Length (Cm) Thickness of wire (mm) Resistance in Ex 1 Resistance in Ex 2 Resistance in Ex 3 Total resistance Average resistance (3s. f) 2 I am now ready to plot two graphs; I have decided to plot the resistance in experiment 3, and the average resistance.
These are highlighted on the table above. Analysing Evidence I have drawn two graphs on the previous pages these consist of the normal readings and the average readings, I have drawn them using the axis: Length of constantan wire on the x-axis in centimetres. Resistance on the y-axis in ohms. I have made these graphs, large because it would then be more accurate, this will help me make note of any anomalous readings and patterns.
To get an idea of what the graphs are supposed to look like, I have drawn a line of best fit. This will show which readings are reliable and which are not. From the graphs, I can see that the resistance of the wire is proportional to the length of the wire. I know this because the Line of Best Fit is a straight line showing that if the length of the wire is increased then the resistance of the wire will also increase. Although, there are minor mistakes in my graphs, my prediction still satisfies the results, because I stated that when the length increases, then the resistance would also increase in proportion to the length.
I said this because the longer the wire is, the more atoms there are and so the more likely the electrons are going to collide with the atoms. I also stated that if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. To explain the minorities of anomalous readings, I can say that it was due to many factors. The reason why I had these anomalous readings was frankly due to the fact that there were some variables, which did not remain constant.
For example, it seemed to me that the voltage did not stay the same, because when I recorded the voltage in the experiment, I found that it did not remain constant, this may have happened because we were using lots of short wires connected together. Another example is the fact that the crocodile clips were not put exactly on the point needed, I know this because when I placed the crocodile clip at 120cm and 140cm I found that it measured the same voltage and same current. The thickness did not stay constant either, as we know from using the micrometer screw gauge, the wire’s thickness varied from allocated places on the wire from 0.30mm to 0. 32mm.
This would have made the resistance decrease. This is because of the increase in the space for the electrons to travel through and due to this increased space between the atoms, there were be fewer collisions. I also know that if the wire were not stretched along the ruler then the thickness of the wire would have made the resistance decrease. Conclusion In my prediction I said that: if the length increases then the resistance will also increase in proportion to the length.
From my graph I have shown that my prediction was correct, as the Line of Best Fit is a straight line proving that the resistance of the wire is proportional to the length of the wire. The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion. The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions, which will increase the resistance of the wire.
If a length of a wire contains a certain number of atoms, when that length is increased the number of atoms will also increase. This is shown in my diagrams below: Wire A Less ions Wire B More ions In this diagram the wire A is half the length of the wire B and so has half the number of atoms, this means that the electrons will collide with the atoms half the amount of times. Also if the length of the wire was trebled or quadrupled then the resistance would also treble or quadruple. Evaluation From my results table and graph I can see that my results that I collected are very reliable.
I know this because my results table only show a couple of minor anomalous results this shows that the one minor reading had made the average results change. Also on the graph I can see that 2 of the averages plotted are anomalous because all the averages lie along the same straight line, but only the 2 circled show further away from the line than others. During my experiment I have noticed several modifications I could make to improve on the Investigation if I was to repeat it, once more. The first of these modifications would be in the circuit that I would use. To be more accurate with my results I would use the following:
Power supply of 4 volts. A digital ammeter, a device that also measures voltage and resistance. A needle instead of a crocodile clip. * A wider ranges of wires not just the constantan, as this would give me varied readings. Instead of connecting the voltmeter to the main circuit I would connect it to the wire, which is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well. To also improve on my results I would use a digital instrument to read the voltage, current and resistance, instead of the analogue instruments.
I would do this because a digital instrument is a lot more accurate than an analogue because if the needle in the analogue voltmeter, for example, is bent then the readings given off will be false whereas a digital voltmeter does not rely on a needle or any other manual movements and the reading error can be made very easily along with the parallax error, on which we have to avoid. The next modification I would make would be to use pointers instead of crocodile clips or maybe even a needle, I would do this because pointers or needles would be more accurate.
The pointers/needles would be more accurate because the tips have a much smaller area on its tip than the crocodile clips giving a more accurate measurement of the length of wire. As well as making these modifications I would also improve my Investigation by testing the same wire but different widths of that wire. I would do this to expand on my Investigation.