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Introduction

GCSE Physics- Ohm's Law coursework Aim: I have chosen to investigate how the resistance of a wire is affected by the length of the wire. What is resistance? Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighboring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat. How is it measured? The resistance of a length of wire is calculated by measuring the current present in the circuit (in series) and the voltage across the wire (in parallel). These measurements are then applied to this formula: V = I ´ R where V = Voltage, I = Current and R = Resistance This can be rearranged to: R = V I Ohm's Law It is also relevant to know of Ohm's Law, which states that the current through a metallic conductor (e.g.

Middle

was decided that 3V would be used in the proper experiment, as it provided more accurate results from 10cm up to 100cm and the higher voltage provided no additional ease of measurement. Furthermore, it was also decided to allow the wire to cool between experiments as considerable heat was noticed at lower lengths and, as mentioned above, an increase in temperature results in an increase in resistance. By allowing the wire to cool between experiments a fair test could be assured. Safety: In order to perform a safe experiment, a low voltage of 3V was chosen so that overheating was minimized. Furthermore, lengths lower than 10cm were not tried, which also helped to avoid overheating. Results Wire 1, Set 1: Length (cm) Voltage (V) Current (A) Resistance (W) (to 2 d.p.) 10 0.66 1.22 0.54 20 0.84 0.89 0.94 30 0.97 0.70 1.39 40 1.06 0.57 1.86 50 1.16 0.50 2.32 60 1.22 0.44 2.77 70 1.25 0.38 3.29 80 1.27 0.35 3.63 90 1.31 0.29 4.52 100 1.33 0.29 4.59 Wire 1, Set 2: Length (cm) Voltage (V) Current (A) Resistance (W) (to 2 d.p.) 10 0.51 1.02 0.50 20 0.79 0.79 0.97 30 0.91 0.65 1.40 40 1.02 0.55 1.85 50 1.08 0.48 2.25 60 1.15 0.42 2.74 70 1.19 0.37 3.22 80 1.22 0.33 3.70 90 1.26 0.30 4.20 100 1.27 0.28 4.54 Having completed two sets of results for one wire, it was noticed that

Conclusion

Generally speaking, wire 1 would appear to contain the most accurate results due to the fact that all of its points bar one sit on the line of best fit for that wire. The only one that does not is the point at 90cm, which was exactly at the point that the black mark (mentioned previously) was found to be. Wire 2, on the other hand, had three main anomalous results: at 50, 80 and 90cm. They are by no means that far off but in an experiment such as this, which is generally a very accurate one anyway, such anomalous results should not be quite so common. Possible explanations for these anomalies are that the length of wire for that particular measurement was not correct. At 50 and 80cm it is possible that the length was shorter, causing a lower resistance, and at 90cm it is possible that it was longer, causing a higher resistance. The solution to this is to measure the lengths more carefully and ensure that the wire is pulled tight against the metre rule. For a particular result, one or more of the connections could have been faulty, causing extra resistance at the connections. A solution to this would be to, before each experiment, connect the connections together without the wire in place and measure the resistance then. If it is higher than it should be then the connections could be cleaned. Overall I think that the experiment was successful and I was very pleased with my results and with my early prediction.