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# An investigation intoThe resistance of a wire

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Introduction

An investigation into The resistance of a wire Physics Coursework Ben Smith, 10S Aim: To discover if a relationship exists between the length and resistance of a wire. Prediction: I believe that I will discover that the resistance of a wire increases proportionally with the length. I think that this is due to the way resistance occurs in a typical wire. Resistance is the result of negatively charged electrons (the actual current) colliding with the positively charged ions that make up the wire. The collisions cause the energy in the electron to be lost, and when they occur on a larger scale there is a noticeable difference between the start and end voltage of a circuit. As the length of the wire increases, so must the number of particles. As the number of particles increases, so will the number of collisions, and therefore the amount of resistance encountered. George Ohm discovered that the voltage of a circuit is directly proportional to the current flowing through the circuit, meaning that if you triple one, you triple the other. He then came up with a rule for working out the resistance of a circuit (rearranged from his original equation): Resistance = Current / Voltage This is the formula I will use to calculate the resistance of the wire. A wire, showing collisions occurring If you double the length of the wire, I believe you will double the resistance. ...read more.

Middle

As a result of potentially dangerous incidents with lesser wires, I added the safety point concerning time: the longer any wire is left with current running through it, the hotter it gets. Measurements I am going to test the chosen wire at voltages between 2 and 9 volts, the safe maximum for my chosen gauge. This should give a range of results to compare. The lengths I believe will provide the most easily comparable results are 20,40 and 80 cm, 25, 50 and 100 cm, and 30 and 60cm. You will notice that the series are multiples of one another: this allows me to test my hypothesis (of direct proportionality) several times. I have decided not to carry out replicates because there are not enough variables to warrant them. If I follow my plan correctly, human error is unlikely and should be obvious, giving a chance to repeat the reading. Carrying out the experiment: Method: I followed the plan I originally decided upon, including the modifications I made as a result of the pilot experiment. I used the chosen NiChrome 34gauge wire, at the voltages and measurements discussed above. Results: Here is a chart showing the data I collected. It will allow me to calculate the resistance (using Ohm's law) later. Length of wire (in centimetres) Voltages tested (V) ...read more.

Conclusion

This may be due to the fact that I started my experiment at 100cm, before moving along to shorter lengths, and as I progressed I become more competent at taking readings. Alternatively, this may be due to the state of the wire, a factor I didn't take into account. However, these variances didn't affect my results. My final results are also very close to those from the Standardised Table of Results, but are slightly higher, indicating a marginally higher overall resistance (present across the readings). There are numerous ways in which this overhead occurred - perhaps due to equipment or method used - but my theory of a directly-proportional increase still remains correct, because all my readings have this gain. Consequently, my readings are still accurate, and my prediction correct. I had no anomalous (or "freak") results and all my results showed strong positive correlation, as expected. My results were very close to the official figures showing how accurately I carried out the experiment, which in turn gave me very reliable figures. Overall, the evidence I gathered was of sufficient accuracy and reliability to allow me to prove my hypothesis and draw a successful conclusion. If I wished to improve the experiment, I could attempt to improve the accuracy with which I measure the current, perhaps using more accurate equipment. I do not need to increase the number of measurements - the range I had was sufficient. ...read more.

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