The reason we are performing this experiment is because we want to see if ‘The Length of the Wire’ has an affect on the resistance of the wire. Length will be the variable in this experiment.
Prediction
I predict that as the length of the wire is increased the resistance will increase and as the length is decreased the resistance will do the same. I believe this because I know that if the electrons in a current have further to travel then the resistance will increase. I also believe that as the resistance increases the voltage must increase because there needs to be more power pushing the electrons through.
Planned Method
For this experiment the length of wire will have to be altered for each individual test. The first I will do is link up an Ammeter, a power supply and a variable resistor in a series circuit using connecting wires. In between, I will connect a 1 metre ruler with a long piece of wire taped on to it, with crocodile clips joint to the wire on both sides, however, one clip will be moved along the wire whilst one stays at 0cm. Parallel to the circuit, I will connect a Voltmeter using connecting wires. I determine that I will make the length of the wire increase by 10cm each time. This figure is chosen because it is a rounded number and would be small enough to record the difference in resistance, and large enough for there to be a considerable change in resistance. I will use a variable resistor to control the current in the circuit. I have decided that I will record 11 results ranging from 0cm to 100cm, so that this would result in a wide range of resistances.
Fair Test
The power supply used in the circuit stayed the same throughout as if I changed the cell, and one was older than the other, then one would have had a lower voltage than the younger cell. Also the wires used to connect the components into a circuit stayed the same. The same type of Ammeter and Voltmeter were used in order to fully control the experiment. The length of wire being tested was measured accurately against a ruler and clipped tightly into the circuit. The experiment was repeated for each different length so as I got accurate and fairly reliable results.
Safety and Risk Assessment
Care was needed during this experiment because the mains power supply was needed and wet hands touching the sockets would result in an electric shock. The equipment was very expensive and had to be dealt with carefully. I had to make sure the wires were connected correctly so as no equipment would be damaged or ‘blown up’.
Proposed Results Table
Obtaining Evidence
I have not made any changes to my planned method as everything ran smoothly during my experiment. However, due to time wasted in setting up equipment and putting it away again, I had to perform my experiment over a 2 day period in order to obtain a full set of reliable results. I kept all the variables constant apart from the length of the wire so as it would be a fair test.
Results
Length Vs. Average Resistance
Conclusion
The table above and my graph shows that as the length of the wire increases, the resistance also increases. My hypothesis is proven to be correct, just as I had predicted. This has happened because if the wire is longer, the more collision the free electrons will have so they will be slowed down and the current will be low, leaving the resistance high. As you move down the x-axis on my graph, the co-ordinates are plotted higher which means the line will be increasing. The results were slightly less accurate; nevertheless, they were accurate enough to produce a good directly proportional straight line graph. I think performing my experiment 3 times helped find more accurate results as I found out the average of the resistance of the wires at each length. Inaccuracy in the results may have been due to the fact that the equipment used may not have been working properly. Also, when measuring the length of wire to be tested, it is possible that I may have slightly misread the length on the ruler by a couple of millimetres because of kinks and twists in the wire making it nearly impossible to get a perfectly straight piece of wire.
