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However, if the reading on the ammeter or voltmeter was not taken quickly, the temperature may have risen, and therefore the resistance of the wire would have increased too. This would mean that the results would not be totally accurate, as the experiments would not be fair. 2. There may have been some problems with the equipment that would help explain possible anomalies other than human error. For example, the wire used may not be pure, and the equipment was not totally accurate, due to frequent use, and the fact that it was built and maintained to a poor standard.
3. As different lengths of wire needed to be used, I cut separate lengths of Constantan wire, instead of using the same section of wire and varying the points at which the crocodile was connected. It is probable that each separate section of wire had different amounts of impurities in them, and therefore the readings will not be entirely accurate. 4. Some of the anomalies will have been caused by human error in the measuring of the wire. This is because it is not very practical to hold a piece of wire straight and cut it perfectly at the designated length.
The crocodile clips will also have not been placed exactly at the specific length, and so the actual length of the wire in the circuits will vary from the length recorded. 5. The crocodile clips used were partially rusted in places, and that would have prevented them from forming a good connection with the wire. They were not connected securely as they were old and much used so that the clips could be easily moved to alter the length. Although there were many chances for an error to occur, there are none that obviously stand out.
I do not feel, however, that the use of a thin wire in this experiment was a suitable choice, as the wire was never truly straight. It would be better to use a less malleable metal material, such as a bar, or in fact just to use the rheostat, as it is a long piece of coiled wire that can be connected at different lengths to change the resistance of the circuit. Experiment Two: Investigation into how varying the cross-sectional area of a wire will affect its resistance. Fair Test: In order to ensure that the experiment is as fair as possible, only one factor will be varied: the cross-sectional area of the wire.
The other factors will be kept constant as shown below: The length of the wire will be kept constant at 40cm, as this factor has been explored in the experiment investigating length. I will be using Constantan wire throughout, as there were a larger variety of thicknesses available to me with this material. The temperature of the wires at the start must be the same so as to guarantee that a fair test is carried out. The temperature must be kept at room temperature, so that the electrons in the wire are not given differing amount of energy. Method: Safety: Precautions must be taken so that no water gets near any of the electrical appliances.
It is imperative that you do not touch or place loose wires onto the wire that is being tested as it becomes hot during the experiment. Leave the wire after the experiment for a brief period in order to let the wire cool before touching. Apparatus: Varying cross-sectional areas of Constantan wire (as designated in plan) to be tested, all 40cm in length Rheostat Power supply Voltmeter Ammeter 2 connecting wires with crocodile clips 4 connecting wires A 1 metre ruler Scissors The following circuit was used in the experiment investigating the cross-sectional area: Plan: 1.
Connect circuit as shown in diagram above 2. Insert first cross-sectional area of wire to be tested into the circuit, in this case: 22 SWG. 3. Turn on the power supply and quickly take readings from both the ammeter and the voltmeter. 4. Repeat until all the following thickness’ have been tested and have had readings taken: a. 22 SWG b. 26 SWG c. 28 SWG d. 32 SWG e. 34 SWG As already mentioned in the experiment investigating length, the power supply used was built so that 6 amps was the maximum current allowed to pass through the circuit, and again I chose to set the power pack on 4 volts.
The whole experiment must be repeated 3 times for accuracy, and then an average of these will be taken and used in the results table and graph. To make sure that the experiment is as accurate as possible, the wire being tested must be held straight, so that it does not come into contact with anything but the crocodile clips, and so that there are no bends in the wire. This is to ensure that it does not short circuit or affect the resistance, so as to make certain that the readings are not jeopardized.
The readings must also be taken quickly after completion of the circuit, so that the current passing through the wire does not affect the temperature, and possibly resulting in an increase in the resistance that will provide confusing results. Upon testing the experiment I have come to the conclusion that the plan will produce accurate readings and very few errors. With it, I was able to obtain these results: Results: Thickness of wire (SWG) Average Voltage (V) (Volts) Average Current (I) (Amps) Resistance (R) (to 2d. p)
The standard wire gauge (SWG) can be used to find out the radius. From this we can use the formula below to work out the cross-sectional area in mmi?? : ?ri?? Thickness of wire (SWG) Radius of wire (to 2d. p) (mm) Cross-sectional area (to 2d. p) (mmi?? ) 1/cross-sectional area (reciprocal) (to 2. Observations: Again, as in the first experiment, I noticed that the readings on the voltmeter and ammeter flickered between numbers, and so I took the first number as the most accurate measurement due to the effects of temperature change.
At the beginning of the experiment I was also going to test a Constantan wire of 30 SWG, but when testing this wire it provided me with the same results as that of 32 SWG. This probably meant one of the wires was marked incorrectly, so I only used one of them and marked it as 32 SWG as this followed the curve of my graph. Anomalies: The graph implies that my reading for the resistance of the 28 SWG wire was incorrect, as it differs about 0. 85 ? from my line of best fit. This is probably because the wires were mixed up (as this had already occurred), as the result for this wire fits in with my line of best fit for a thickness of about 31 SWG.
Conclusions: In view of my results and the graph I was able to construct from them, I have made the following conclusions: a. As predicted, when the cross-sectional area of the wire increased, the resistance also increased. b. The graph shows a strong trend forming a curved line, showing that the cross-sectional area of a conductor is inversely proportional to the resistance (as shown in the graph recording the reciprocal of the cross-sectional area): as the cross-sectional area doubles, the resistance will halve.
From my analysis, I can say that my prediction was correct. This can be proved by carefully studying both electricity and electrical conductors. Electricity is the flow of energy from one place to another. Metal electrical conductors enable energy to be passed through them by containing a ‘sea’ of freely mobile electrons, which carry the energy. When the electrons in the conductor are given enough energy, they are able to move from one end of the conductor to another, and therefore create a current.
There is only a certain amount of space for the electrons to move in the conductor, and so collisions may occur between the electrons and any other immobile particles contained in the conductor. If the width (cross-sectional area) of the conductor, in this case a wire, is doubled, the electrons have double the amount of space, and so the probability of a collision between the electrons and any immobile or impurities in the wire is halved. This means that half the amount of electrical energy is being converted into heat energy by collisions, and so the resistance is also halved.
Evaluation: There were a few mistakes in my experiment, mainly caused by carelessness in the storage of the materials used: 1. I included a rheostat in my circuit, but I did not adjust it for each reading (to control the current) as I believed that leaving the circuit connected for a long period of time would considerably alter the temperature of the wire, as collisions occurred and electrical energy was converted into heat, so the current readings vary slightly, which I believe will produce varying temperatures, but none so dramatically as to render my results totally inaccurate.
2. However, I attempted to take the readings for the ammeter and voltmeter quickly so that any temperature change would be very slight and would not affect the results. 3. There were some problems with the equipment I used throughout this experiment. The apparatus was not totally accurate as it was built and maintained to a poor standard due to lack of funds, for example the crocodile clips were coated in rust, and so the contact between it and the wire was not perfect. The wires were labelled incorrectly so the results were confusing.
4. Some of the anomalies will have been caused by human error in the measuring of the wire. This is because it is not very practical to hold a piece of wire straight and cut it perfectly at the designated length. The crocodile clips will also have not been placed exactly at the specific length, and so the actual length of the wire in the circuits will vary from the length recorded. Although there were a few mistakes in this experiment, on the whole I do believe that they provided me with a good basis for my conclusions.