Other factors, which we need to consider when finding the resistance of a material, length of wire, thickness of wire, and temperature of environment around circuit.
Experiment plan:
In this experiment we will measure the resistance in a circuit, with varying lengths of wire and compare how the length of wire affects the resistance. The experiment should be fairly simple it only needs to involve testing different lengths of one type of wire. There is no range limit to how long the wire should be but it probably won’t exceed one meter due to practicality reasons. In this experiment we will need to use a simple electrical circuit with power from a power pack. To calculate the resistance of the circuit using ohms law, both ammeter and voltmeter will be required (voltage / current = Resistance.) The wire that will be varying in length will needed to be connected to the circuit in series so that the current flows directly through it. Power will need to be supplied through a D.C power pack so that power can be measured accurately to ensure that it is the same each time we repeat the experiment.
This is what my circuit will look like:
There will be a thin piece of copper wire stretched over a meter ruler. This will be the wire that we will vary the length of. A crocodile clip or “slider” attached to the end of a normal wire will be able to slide up and down the wire stretched over the ruler so we can change the length of the wire easily. Resistance recordings will be taken while the current is flowing through 20cm – 90cm of wire. To obtain an average result the experiment will be repeated at least twice for more accurate results and also to account for any anomalies that might be in our results.
I will conduct each experiment using this order of events each time:
- Slide the crocodile clip to 10cm of the meter ruler
- Apply current
- Record readings from voltmeter and ammeter
- Calculate resistance.
The same steps will be taken for 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm and 90cm. I will then repeat the experiment at least one other time so as I can work out an average resistance for each particular measurement. I may decide after my preliminary experiment that I need to take more measurements in order to have more accurate results.
Prediction:
Using my scientific knowledge of resistance of wires plus the research that I have been doing I can predict that the resistance will increase in proportion to the length of the wire, when the wire is 20cm long there will be a low level of resistance. I predict this because I know that if there is a short length of wire there will less length for the current to travel through meaning fewer collisions between the atoms in the wire and the electrons in the current. Also as the electrons in the current pass through the wire they have to squeeze together meaning a loss of energy due to friction between the electrons, if the length of wire that the current is passing through is shorter the electrons will not need to squeeze together for as long a period of time so less energy will be lost. This will also work the same way if the wire is very long, the wire that is 90 cm long will have a much higher resistance due to more collisions between electrons and atoms. I would also predict that the resistance of the circuit would only increase in proportion to the size of the wire. E.g. the length of wire is 40cm, the resistance will be double what it would be if the length of the wire was 20cm. The resistance should be considerably higher at 90cm of wire then it is at just 20cm of wire, theoretically the resistance should be exactly 4.5 times as great at 90 cm then it is at 20. However this may not prove to be exactly true when we take out the experiment because there are also factors such as impurities in the wire that will affect the resistance of the circuit. Unfortunately we cannot do anything about this to make the experiment fairer.
Preliminary experiment:
Before I decide to start my investigating I need to conduct a preliminary experiment, this I where I try out the experiment so as any gaps in the planning or any parts of the plan that I have made that aren’t practical or don’t work can be changed for the fial experiments.
Our preliminary experiment results:
Our preliminary experiment went fairly well although there were a few things that could be improved:
We need to do more measurements so as our results are more accurate.
During our experiment the wire kept coming loose from the ruler making our measurements inaccurate. To improve this we could stick the ends of the wire down to the ruler with tape.
I have also decided that only reading measurements every 10cm is not enough to get the level of accuracy that we need for this experiment, therefore I have decided to take readings every 5cm, making the measurements that I am taking more accurate.
Observation
I decided to repeat the experiment 3 times to make my results as accurate as possible in the time that was allocated I have then worked out the averages from each of the 3 experiments by adding all the results from the 3 tests and dividing the answer by 3, I then used these averages to work out the resistance of the wire (last column). After this I used the resistances that I had worked out and put them into a graph
Analysis
Below is a graph of my results that shows how the resistance of a circuit increases in proportion to the length of a wire:
As you can see the graph is a clear example of showing how resistance rises as length of wire increases. The points on the graph are in fairly good correlation and seem to follow my prediction well. As I predicted the resistance increases in proportion to the length of wire. I also predicted that there would be a distinct pattern that the levels of resistance will follow.
I will now test if that it true.
I predicted that that the resistance of a wire that was 40cm long would be double that of the resistance of a 20cm piece of wire.
The resistance of a wire of 40cm = 12.54
The resistance of a wire of 20cm = 6.5
6.5 x 2 = 13
12.54 is very close to this number thus proving my theory correct
The results and calculations aren’t exactly as perfect as they should be in theory this could be partially due to impurities in the wire.
Evaluation
I think that this experiment was an overall success, the results that I obtained from the experiment showed a clear pattern and they followed my hypothesis almost exactly. If I were to repeat my experiment again I could have measured the natural resistance of my circuit and then taken this into account when calculating the resistance, as this was one of the only factors that has made my results inaccurate. Given more time and better equipment this experiment could have been more accurate but with the given circumstances it went well and there aren’t many things that I could have done to improve it.
