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To investigate the affect of wire width on electric current and resistance.

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COURSE WORK PIECE 1: RESISTANCE HARRY HUDSON 10U 25/5/02 AIM: To investigate the affect of wire width on electric current and resistance. INTRODUCTION: What is electricity? Electricity is the phenomena resulting from the existence of charge. The units of charge are: one electron (negative charge) and one proton (positive charge). All normal atoms contain both of these particles, as well as neutrons (neutral charge). All solid metals contain atoms arranged in a regular structure. One or two electrons per atom are weakly attracted as they are further from the nucleus and are held in by a weaker force, and thus may move away from the atom and "wander" through the metal. The loss, or gain moveable electrons means the material has positive or negative charge. The main units used to measure electrical quantity are: ampere (unit of current), the coulomb (unit of charge), and the volt (measurement of electromotive force). What is current? Current is the term used to denote a flow of electric charge. This is known as ELECTRODYNAMICS, as we witness charge in motion. Electrons may flow through any material known as a conductor (all metals). The reason for this is the `free' electrons moving within the metals structure. In order for current to exist in a conductor, there must be an electromotive force (emf), or potential difference in charge at the two ends of the conductor; (the magnitude of potential difference (p.d) is measured in Volts). An emf such as, a battery with a positive and negative terminal supplies direct current, (flow in one constant direction). This is known as DC. In the presence of an emf these `free' electrons are attracted to the positive charge; thus creating a movement, or `flow' of electrons known as current. The reason for the movement of the electrons toward the positive charge is that `opposites attract'. What this means is that opposite charges are attracted to one another, in order to balance their charge so that they may become neutral. ...read more.


The coil of wire was unwound, and measured against the meter ruler accurately to ensure that he length of wire tested is as accurate as possible. For the 20cm, and 100cm tests of the same thickness, and material, the same wire was used to ensure as little variation in the wire as possible. The readings were taken as soon as the circuit was switched on, to ensure that the initial result was taken, and not the result after the circuit had heated up. We also tested the circuit before the length or wire was put in place to ensure that the circuit wasn't affected by any other variables. Results of preliminary test: Length (cm) Material Thickness Voltage (V) Amps (A) Resistance (Ohms) 100.0cm Copper Thin 1.37 1.82 0.753 20.0cm Thin 0.520 2.32 0.224 100.0cm Medium 0.820 2.28 0.360 20.0cm Medium 0.260 2.58 0.101 100.0cm Thick 0.540 2.56 0.211 20.0cm Thick 0.140 2.72 0.0515 100.0cm Constantan Thin 3.62 0.220 16.5 20.0cm Thin 2.80 0.810 3.46 100.0cm Medium 3.41 0.400 8.53 20.0cm Medium 2.27 1.24 1.83 100.0cm Thick 3.13 0.630 4.97 20.0cm Thick 1.67 1.68 0.994 All measurements given to three significant figures What is learnt? : This preliminary test is successful in showing us which values we should set the dependant variables at, and generally how to conduct the test successfully. We firstly see that the resistance of constantan is much greater than that of copper. Therefore a much smaller percentage of the total resistance is created by the other wires and equipment in the circuit. The resistance measured for constantan is therefore much more accurate. We can see this in the results, using the idea that length and resistance are proportional to judge accuracy. We also see that the thicker the wire the less resistance. It is undesirable to make the resistance low, as it will mean a greater percentage of each results will be error due to the other variables in the circuit. ...read more.


For example, my measurement of the ammeter of voltmeter may be inaccurate; the wire may not return to the same temperature in the cooling time allowed; the lengths of wire may not be totally precise. This is reflected in the variation, however slight in the repeated tests. In an ideal situation the repeated tests would show identical results for each test. If I were to repeat this experiment with greater time and facilities I would make the following changes to the procedure, to improve the accuracy of the experiment. To improve the accuracy of the wire measurement I would use pointers instead of crocodile clips, as they take up less area, this meaning the length of wire is more accurate. I would set up a computerized system to maintain temperature in the wire, and to measure more accurately the voltage and current in the wire when the system is at the same temperature. Low resistance equipment would be used so that a much smaller percentage of the resistance result is due to the equipment. To make the experiment more wide-ranging and valid to the hypothesis the following improvements could be made: another investigation could be carried out on different diameters of wire to see the proportionality in different diameters of wire; a different material could be used, which will have a different level of resistance and again test proportionality; a greater range of results may be taken to see if proportionality is maintained across such large ranges. I could also develop the investigation by looking at the other variables, and making other hypotheses from the scientific knowledge, thus extending my investigation and allowing the conclusion to be greater validated. These could include looking further at the affects of temperature and diameter by looking at many more diameters of wire, and the affects of different temperatures. Also, with a lower resistance equipment system, some other lower resistance materials may be investigated. These would all provide a more developed and accurate investigation, yet the experiment conducted was relevant to investigating the topic, and the hypothesis was successfully proven in the time given. ...read more.

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