The wire will be attached to a meter ruler so the measurements taken will be as accurate as possible. Readings will be taken form the ammeter and voltmeter at 10cm intervals along the wire, starting at zero and finishing at 100cm. This will give me a sufficient range of data to prove or disprove the prediction and meet the aim of the investigation, any less and there would not be enough information to form an accurate conclusion.
At each 10 cm reading the results will be taken three times, and an average will be deduced form this to make the results gained as accurate as possible.
In order to work out the resistance of the wire, the current and voltage will be recorded at each 10cm of wire, this will be done by connected a voltmeter which measures the amount of volts in the circuit and an ammeter which records the current (amps) in the circuit.
The voltmeter is connected in parallel with the nichrome wire so that it gives a true reading of its resistance, which it would not do if it were connected in series. The ammeter however must be connected in series to measure the current flowing through the circuit.
Once these readings are recorded the resistance of the wire will be worked out by using this formula.
V = IR
Therefore
Resistance in Ω = Potential difference (V)
Current (A)
The results will be recorded to 2 decimal places, as this is a reasonable degree of accuracy.
Fair Test
To ensure that the investigation is a fair test the following factors will be considered as they could influence the outcome of the results.
- The type of wire (nichrome) as different types of wires may have slightly different resistances
- The voltage input, as a higher voltage will provide more "push" to the electrons.
- Any other equipment such as the ammeters, voltmeters, battery pack and connecting wires, as changing theses around could throw off the results due to small indifferences.
These factors will be controlled by keeping them constant, and only changing the length of the nichrome wire so that they will not affect its resistance.
In order to ensure the investigation was feasible, a preliminary experiment was carried out in which the resistance of nichrome wire was tested at the beginning, middle, and end of the wire. The results showed that to work out the resistance of the wire, the equation above would be the best method to use, and that the wire should be attached to a ruler to make it easier to measure which helped to finalise the plan.
Results Table
The results of the investigation are in the table on the next page; the initial rough table is attached along with the graph of the results.
The results recorded appear to match the prediction so the investigation will not be repeated.
Analysis and Conclusion
The results obtained show that the prediction was correct; as the length of wire increases, as does the resistance. The graph shows that as the line of best fit passes directly through the origin, the length of the wire is directly proportional to its resistance, as stated in the hypothesis. The pattern shown in the graph clearly matches the predicted sketch graph in the hypothesis, showing that there is a definite relationship between the length of the wire and its resistance.
This pattern occurs because as the electrons flow though the wire they have to "push" against its resistance, when the length of the wire increases the electrons have to "push" harder in order to travel further, meaning its resistance is increased.
Evaluation
The investigation went as planned, the procedure was well carried out, which is proved by the excellent results obtained. As shown by the graph the results match the hypothesis by a fair degree of accuracy, matching the pattern expected.
The quality of the results were good, with no anomalous results found. The evidence gathered was valid as there was nothing that went wrong which could have influenced the experiment in any way, any factors which could were controlled to ensure the experiment was a fair test.
All the evidence collected supports the conclusion, although to be certain the experiment could be repeated to verify that the entire set of results were not anomalous, and be further accurate in the conclusion.
The investigation was relatively easy to carry out, as it did not involve any complex procedures. If the experiment were to be repeated, instead of using ammeters and voltmeters to work out the resistance, it could be improved if a multi-reader was used which could work out the resistance automatically. This would ensure that the results were accurate, and make the investigation less time consuming, and easier.
To obtain more evidence in support of the conclusion, background research could be done into the theory of resistance to ensure that the evidence collected is correct and further experiments could be carried out with more results to see how the pattern develops.
