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# To find out how the resistance changes as the length of the wire changes.

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Introduction

Coursework: Resistance of a Wire Aim To find out how the resistance changes as the length of the wire changes Equipment > Constantan Wire 1m > Power Pack - 4V > Digital Ammeter > Digital Voltmeter > 3 x Crocodile clips > 3 x Crocodile/plugs > Metre rule. Variables The independent variable is the length of the wire. This will be measured with a metre rule and the range of the length will be 10cm to 100cm increasing by 10cm each time. The dependant variable is the resistance. The resistance will be measured by dividing the average result for the voltage by the average result for the current - Resistance = Voltage/Current The control variables are the thickness, temperature and the type of wire. Method Measure three lots of the same of the same length of constantan wire Connect up the circuit; as shown in the diagram below, ammeter in series, voltmeter in parallel to the component (wire). Record the results for each length from the ammeter and voltmeter and take the average. Using the results, work out the resistance - R=V/I Make sure the power supply is switched off when not in use. Obtaining Results I will use my equipment to obtain my results by using the ammeter to measure the current and the voltmeter to measure the voltage. ...read more.

Middle

As they move they bump into the metal ions. The metal ions are surrounded by a "cloud" or "sea" of electrons. Because of the structure of a metal they behave as conductors. The metal atoms release their outer electrons to form an electron cloud throughout the structure. The power pack is supplying the energy to the electrons to make them move, so they are gaining kinetic energy. The collisions occur between the free moving electrons and the positive ions of the conductor that are vibrating about their mean position - but they are not free to move around the metal. This causes the electrons to lose kinetic energy whilst the ions vibrate more vigorously. The more energy that is spent forcing the electrons through, the greater the resistance of the material. Results Current (A) Voltage (V) Resistance (?) Length (cm) 1 2 3 Average 1 2 3 Average 1 2 3 Average 10 0.95 0.94 0.96 0.95 0.30 0.30 0.31 0.30 0.32 0.32 0.32 0.32 20 0.67 0.68 0.64 0.66 0.44 0.42 0.42 0.42 0.66 0.62 0.61 0.64 30 0.43 0.47 0.48 0.46 0.45 0.48 0.50 0.48 1.05 1.02 1.04 1.04 40 0.40 0.41 0.42 0.41 0.55 0.56 0.57 0.56 1.38 1.37 1.36 1.37 50 0.32 0.30 0.32 0.31 0.62 0.58 0.61 0.60 1.94 1.93 2.03 1.94 60 0.30 0.31 0.30 0.30 0.64 0.64 0.65 0.64 2.13 2.06 2.10 2.13 70 0.28 ...read more.

Conclusion

Results Wire Current (A) Voltage (V) Resistance (?) Nichrome 0.94 1.98 2.1 Constantan 0.32 2.35 7.3 Conclusions From my results I have found that the best type of wire to use is Constantan because it gives more resistance. The thickness of the wire that we used was fine and as we had a choice of three; 24s.w.g, 26s.w.g and 32s.w.g so we chose the middle one as it won't get too hot but it won't be too thin. 24s.wg is the thickest wire. The heat on the outside didn't affect the constantan wire so by using this wire in my actual investigation I won't need to use a water bath for the experiment and I get the best resistance. The measurement of resistance will definitely be made by taking the results from the ammeter and the voltmeter in conjunction with Ohms law: "The current flowing through a metal wire is proportional to the potential difference (P.D) across it (providing the temperature remains constant)". From doing this experiment I found that a rheostat wasn't needed as we were repeating the readings from doing three experiments for each length of wire. In the experiment, we took the length of wire as 1 metre and we found that this gave us a good reading and so we are going to use a large range of lengths - 10 cm to 100cm. ...read more.

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