- How much light is on the wire.
I have chosen to investigate how the length of the wire effects its resistance as it is the simplest of all the above to measure. The other factors will have to be kept constant in order for the experiment to be a fair test. The thickness of the wire will be easy to keep the same throughout as will the material that the wire is made from. However, the temperature of the wire and how much light there is on the wire will be hard to keep constant. Although, it is expected that these two factors will not vary too much during the experiment.
Method for Preliminary Experiment
To investigate how the length of the wire effects its resistance, an experiment will be performed in which a constant current will be flown through different lengths of wire and the voltage will be recorded. A variable resistor will be used to keep the current constant as the lengths change. A voltmeter will be used to record the voltage. The voltmeter that will be used can record the voltage to two decimal places which should produce precise results. The voltages recorded from the experiment can be used to find the resistance of the wire for each length using the formula: R=V/I. The resistance will be calculated to two decimal places as a more precise resistance cannot be calculated without being unreliable from a voltage recorded to two decimal places.
This diagram shows how the preliminary experiment will be set up:
Preliminary experiment
A preliminary experiment was performed to attempt to determine:
- What voltage to set the power pack to.
- What lengths of wire to investigate.
- What amperage to keep the current at.
- A suitable extent and range of evidence to be collected.
- How many times to repeat the experiment.
The circuit was set up as shown above in the method and these results were acquired in the preliminary experiment:
Method for the Main Experiment
The set up of the preliminary experiment was successful so it will be kept the same for the main experiment. The voltage chosen to set the power pack to was 8V as any voltage much higher than this resulted in the wire beginning to melt. I have chosen to use 10 different lengths of wire between 10 and 100cm as these will provide a suitable extent and range of results. The current was chosen to be kept at 0.5A as this is a good number for the calculations of the resistance and the variable resistor can keep the current at this point when the wire is between 5cm and 100cm. Occasionally, anomalous results were received. In order to overcome this problem of recording inaccurate results, The experiment will be repeated until three sets of results are acquired with no anomalies.
Prediction
I predict that increasing the length of the wire will increase its resistance because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion. That is, doubling the wires length will double its resistance. The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is doubled the number of atoms will also double. This means that the length of wire is proportional to its resistance so if you double the length of a wire, you double its resistance.
