Current (A)
Analysis
The results show that my prediction was correct. The 2V setting produced far too little numbers and some of them were decimal points. The 6V setting numbers were quite high and the current somewhat halved every time the length was reduced by 400mm. This is too much of a change for 400mm so I think the heat energy that was produced affected the results.
Evaluation
My results were quite good because there were no serious anomalies. The accuracy of the preliminary investigation was good. I think that I would need to repeat each experiment to improve the accuracy.
Main Investigation
Resistance is a material's opposition to the flow of electric current. Resistance can be affected by length, width, material used and temperature. I will investigate the effect of length. Resistance is measured in ohms (Ω). The formula to calculate resistance is
R = V Resistance = Voltage
I Current
Plan
I will investigate the effect on resistance when changing the length of a wire by conducting an experiment that will enable me to do so. I will record the voltage and the current each time I change the length of the wire. I will measure the current and voltage using an ammeter and a voltmeter. I am going to repeat this experiment 3 times to ensure that the results are correct. I will then average these results and use them to calculate the resistance. I will use the same equipment throughout the investigation making it a fair test.
Prediction
I predict that the resistance will increase as the length of wire increases. I think this because length affects resistance. As the wire gets longer, there will be more free electrons for the electrical current to pass around. The resistance of a piece of wire (or component) tells us how much it slows the current down. If the free electrons are slowing down the electrical current, the resistance will be higher. For the same voltage, current flows more easily through a low resistance wire than a high resistance one.
This diagram shows the electrical current having to move around the free electrons, causing resistance and slowing down the current altogether.
Equipment List
Power pack
Length of wire
Wires
Crocodile clips
Ammeter
Voltmeter
Method
I will use various lengths of wire starting from 200mm and ascending in 100mm gaps until the wire is1000mm. I won’t do the experiment with a length of wire shorter than 200mm because the wire will get hot and cause irregularities as temperature affects resistance. I will adjust the length of wire using crocodile clips. For each length, I will record the current and voltage. I will repeat this experiment 3 times. I will then draw a graph using the average resistance to display my results to enable me to analyse them easier.
Results
Current
Voltage
I calculated the average resistance by dividing the average voltage by the average current.
Analysis
Evaluation
I think my results are reasonably reliable and accurate but do have a few anomalies. As resistance is proportional to length, the best fit line on my graph should go through zero and the majority, if not all the points on my graph. However, there are 3 points either side of the best fit line. I think that the three points that are above the best fit line have been caused by heat energy raising the temperature and therefore raising the resistance as the wires probably became too hot during the experiments. I think that the three points below the line have possibly been cause by loose crocodile clips. This would have caused the reading to be inaccurate. If the crocodile clips were not connected securely, the voltmeter and ammeter would have read the voltage and current to be lower than the actual voltage and current.
