In the preliminary experiment, equipment was set up using a power pack, a metre of wire, attached to other wires using crocodile clips, and a variable resistor. A voltmeter and an ammeter were also in the circuit to measure the results.
Preliminary results:
From the preliminary experiment it was decided that the readings will be taken at 8 different lengths, each 10cm apart, ranging from 30cm to 1m. The variable resistor will also change the voltage through the wire 7 times at each length.
Equipment:
- Power pack
- Ammeter
- Voltmeter
- Variable resistor (rheostat)
- Masking tape
- 2 crocodile clips
- Metre ruler
- 6 wires
- 1m Nichrome wire
Method:
Equipment was set up as in the diagram below.
A power pack was plugged into the main power supply and 4 wires were used to create a circuit with an ammeter, voltmeter, variable resistor, and 2 other wires were used to attach the length of nichrome wire with crocodile clips to the circuit. The length of wire was a metre long and this was verified by the fact that it was attached to the metre ruler at both ends, using masking tape, which also kept the length of wire straight. The power pack was then turned on at 4 volts. The variable resistor was used to increase the voltage by 0.2 volts several times, starting at 0.4 volts until 1.6 volts was reached. Each time the voltage was altered the voltage and current were measured and recorded, and seven readings were eventually taken. A crocodile clip was the moved 10cm along the wire and another five readings at different voltages were taken. This was repeated until there were six results for lengths of wire, ranging from 50cm to 1m long, at 10cm intervals. For each different length of wire, readings taken at 7 different voltages varied by the rheostat from a range of 0.4 volts to 1.6 volts, with a difference of 0.2 volts between each reading. Readings were also taken with the wire at lengths of 40cm and 30cm long, however for these results, the voltage of the power pack was reduced from 4 volts to 2 volts for and the seven readings were taken at a range of 0.2 volts to 0.8 volts, with a difference of 0.1 volts between each reading. These small voltages were chosen in order to prevent the voltage from being too high and melting the wire. Overall, there were eight different results, each with seven readings. To keep the results accurate, the experiment was performed in a single room, on the same day and the resistance was calculated on a graph, so that it was not affected by temperature.
Safety Precautions:
Caution was taken in this experiment, to prevent harm to the surrounding area of the experiment and of those performing the experiment. The voltage through the circuit was kept low in order to prevent the wire from growing too hot and melting. Time was also taken between taking each reading, when the power was turned off to allow the wire to cool down, preventing temperature from affecting the experiment. The fact that the results were also recorded on a graph, also made them accurate. The length of wire was not changed by cutting it, which could be dangerous, but by moving a crocodile clip along the wire. While doing this, the wire was also not just touched, just the ruler and plastic covered part of the crocodile clip.
Obtaining
Overall, a sufficient number of readings were taken, as eight results were taken, each with seven readings, so 56 readings were recorded in all. The results were kept accurate by taking several readings, leaving a couple of minutes inbetween each one so that the temperature of the wire did not increase and affect the results. The results do follow the expected pattern, as length of the wire increases so does the resistance. Unlike some experiments, the results were not repeated 3 times in order to obtain more accurate results, because for each result seven readings were taken at different voltages.
Results:
The results are shown in the following tables and have been plotted on graphs.
Readings taken at 1m length of wire
Readings taken at 90cm length of wire
Readings taken at 80cm length of wire
Readings taken at 70cm length of wire
Readings taken at 60cm length of wire
Readings taken at 50cm length of wire
Readings taken at 40cm length of wire
Readings taken at 30cm length of wire
After the results were plotted on the graphs, the graphs were used to calculate the resistance of the wire at different lengths. These overall results are shown below:
Analysis
The results that were plotted on the voltage/current graphs did not show any anomalous points, therefore, they fairly reliable. The final graph shows the relationship between the length of wire and the resistance of the wire. On this graph there is one point which is slightly anomalous, however there is strong positive correlation between the length of wire and the resistance of the wire. In conclusion, the results show that the hypothesis was correct and resistance increases as the length of the wire increases. The relationship between the two axes is directly proportional. This can be seen as the lines of best fit on the graphs are straight and go through the origin. The relationship should be directly proportional because current is the flow of electrons. Resistance is caused by the flow of electrons being halted as the electrons bump into atoms on the wire. In a shorter piece of wire, there are fewer atoms for the electrons to collide with and so the resistance would be lower.
Evaluation
There was sufficient data obtained to support the conclusion, as the results all provide straight line graphs that are relevant to the experiment. From the results tables and the voltage/current graphs it can be concluded that the results are reliable. This is known because there are no anomalous results, and because the results support the hypothesis and scientific knowledge. When the resistances calculated from these graphs were plotted on a new graph against the length of wire, the results are all close to the line of best fit and are fairly evenly spaced, which indicates that they are also reliable. The point for the resistance calculated for the wire at 40cm long, however, was slightly anomalous. This may be because of a human error in the measurement of the results. It is possible that the wire could have been at a slightly higher temperature, thus increasing the resistance calculated, although, it was attempted to maintain a constant temperature by leaving time for the wire to cool down in between each measurement.
To obtain more reliable results, more sensitive equipment could be used to measure the current and voltage of the wire. The experiment could also take place in an environment with a controlled temperature, to prevent fluctuations in room temperature from affecting the results.
To improve the experiment, it could be repeated, possibly with different voltages and different lengths of wire. This would produce more results so that the experiment is more accurate. The experiment could also be repeated with different types of wire to discover whether the hypothesis, as the length of wire increases, the resistance will also increase, is true for different types of wire.