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# Investigating the factors affecting the resistance in a wire

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Introduction

G.C.S.E. Physics Investigation - Factors affecting the resistance in a wire Contents Page 1. Aim.............................................................................................................. 3 2. Introduction................................................................................................. 3 2.1 Resistance 2.2 Ohm's Law 2.3 Standard Wire Gauge 2.4 Factors 3. Method........................................................................................................ 5 3.1 Equipment 3.2 Circuit diagram 3.3 Procedure 3.4 Fair test 3.5 Safety precautions 4. Preliminary work......................................................................................... 7 4.1 Summary 4.2 Parameters 4.3 Experiments 4.4 Conclusions 5. Final Experiment and Results............................................................... 7 5.1 Tables 5.1.1 Preliminary experiments 5.1.2 Final experiment 5.2 Graphs 5.2.1 Preliminary experiments 5.2.2 Final experiment 6. Conclusion................................................................................................ 14 7. Evaluation................................................................................................. 14 1. AIM Our task was to investigate at least one of the factors affecting the resistance in a wire. 2. INTRODUCTION 2.1 Resistance Electricity is conducted by means of free electrons. The free electrons are given energy and therefore move and collide with neighbouring free electrons and so on, transferring their energy along the length of the conductor, in this case a wire. The number of free electrons depends on the material. For example, gold has more free electrons than iron and as a result, it is a better conductor (it has less resistance). The flow of free electrons is called electric current. The resistance of a material is a measure of its opposition to the current. In a wire, this opposition to the current is caused by fixed atoms of metal as well as impurities which the free electrons collide with, converting some of their energy into heat in the process. Resistance is the result of energy loss as heat. It is measured in ohms (?) and can be recorded using an ohmmeter. An object of uniform cross-section will have a resistance proportional to its resistivity and length but inversely proportional to its cross-sectional area. ...read more.

Middle

3.2 Circuit diagram 3.3 Procedure The equipment was set up as shown in the circuit diagram, with the relevant test wire fixed to a metre rule. We pulled the test wire tight so that the current flowed through the exact length of wire that was intended. Firstly, we attached the crocodile clips to the wire, one at the 0 cm position on the metre rule and the other at the length we were testing. Next, we turned on the power supply and recorded the current off the ammeter and the potential difference off the voltmeter as shown on the diagram. This had to be done swiftly because the wires we were testing could warp if we left the power supply on for too long, potentially corrupting our results. After the power supply was turned off the second crocodile clip was moved to the next position. These steps were repeated for each length. We also repeated the entire investigation three times to achieve a greater accuracy. 3.4 Fair test If our investigation was to be successful we needed to make sure that we were not corrupting our results in any way. Therefore, when we were testing our parameters and their effect on the resistance in a wire we ensured that all other factors that affect the resistance remained constant. 3.5 Safety precautions When carrying out experiments, there can be a number of safety hazards. Our main concern was electrocution (see Figure 6). To avoid receiving electric shocks we only used wires that had insulation and were not bare. We also ensured that we were not in the near vicinity of any water sources and that the power supply was turned off before we handled the wires. ...read more.

Conclusion

In addition to this, the wires available were not necessarily of uniform cross-sectional area which could have increased or decreased the resistance. We were unable to control this parameter. Furthermore there were a small number of outliers (Table 4, reading at 80cms) which were most likely due to human error during the measurements. The value obtained for the current was too high, possibly due to inaccuracy of the ammeter. However as we took an average of three readings, this outlier will not have affected our final results. Finally, the room temperature could easily have affected the resistance as it may have changed during the day. Although we completed the entire investigation in one day, there was a noticeable increase in temperature over the time period, which could have increased the resistance in the wires. However measurements with one material would have been completed within approximately 30 minutes, a time period over which the temperature is unlikely to have changed significantly. Therefore I am confident in our conclusion that the length of the wire increases the resistance. I am also confident that denser materials have higher resistance, but the exact values of this increase can only be estimated under more controlled conditions. If we were to repeat these experiments we would undertake them in a controlled temperature environment in a sealed room. Furthermore, it would be advisable to take more repeat readings in the future. If we look at Table 4, we can see the benefits of taking repeat experiments in order to eliminate outliers and arrive at reliable average results. ?? ?? ?? ?? Factors affecting the resistance in a wire Michael Middleton, 10LT 14 Michael Middleton, 10LT 2 ...read more.

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