Type of Material and Diameter:
• I shall get wire from the same reel each time to ensure these factors are kept the same.
Safety:
- Sinks are a hazard; I shall keep the experiment away from them and I will avoid wet damp surfaces because when water and electricity mix, there is a danger of electrocution occurring.
- I shall keep bags and stools out of the way in case someone trips
- I will be cautious over heated resistance wires.
Equipment:
- Resistance wire (material undecided)
Diagram:
Prediction:
I predict that resistance will increase when length is longer because there will be more atoms acting as obstacles for the electrons to get past. Because I am testing the factor of increasing and decreasing the length of resistance wire, I foretell that if the length of a piece of wire is 100cm, the resistance will be twice than it was at 50cm. This is because there will be twice as many atoms acting as obstacles, therefore twice as much resistance as there will be twice as many collisions.
Preliminary Test:
From the preliminary results I have obtained, I have chosen to use wire number 4 for conducting my experiment because it has the largest range of resistance that is 82.3Ω. I have also decided to obtain my results through the power pack voltage of 2V as it gives good results yet will not heat up the wire as much as a power pack voltage of 10V and I will use a wire range of 10cm to 100cm because it also gives good results, whilst still being manageable to conduct the experiment.
Method:
- Collect equipment and set up circuit as shown in the diagram
- Cut wire number 4 to exactly 100cm
- Attach to crocodile clips and switch circuit on
- Obtain results of current and voltage by reading the ammeter and voltmeter and then using the formula shown below to find resistance:
Voltage (V)
Current (A) = Resistance (Ω)
- Repeat steps 2-4 using the following values of length
90cm, 80cm, 70cm, 60cm, 50cm, 40cm, 30cm, 20cm, 10cm
- Repeat the entire experiment twice to find an average result
Results:
Analysis:
From the experiment I have conducted, I have discovered that as I stated in the prediction, that as the length of the wire increases, the resistance of the wire also increases. This is because when the length increases, there are also more particles acting as ‘obstacles’ for the small electrons to get past and so it is increasingly difficult to reach the end of the wire if it is longer as there will be more collisions between the electrons and the atoms.
From my graph;
When a wire length is 30cm, the resistance is 21.0Ω
When a wire length is 60cm, the resistance is 42.5Ω
If 30cm doubled, you would expect to get 42.0Ω
% Error = difference of actual and expected result
expected result x 100
% Error = 0.5
- x 100
% Error = 1.19 %
From my graph;
When a wire length is 40cm, the resistance is 28.0Ω
When a wire length is 80cm, the resistance is 56.5Ω
If 40cm doubled, you would expect to get 56.0Ω
% Error = 0.5
- x 100
% Error = 0.89 %
My percentage errors are very low which means that the experiment I have conducted was very accurate and supports my prediction that when the length of the wire is doubled the resistance doubles as well. They also support the theory of my prediction, that in a 100cm length of wire there are twice as many atoms acting as obstacles than in a 50cm length of wire so therefore resistance is doubled as length is.
Evaluation:
In most cases, my experiment was conducted to a high degree of accuracy. I know this by seeing that my results mostly have a general pattern and the line of best fit is fairly close to my pointes but does not go through them yet there are no extremes; 80cm is my worst result because it is furthest from the line of best fit. The volume, current and resistance are nearly equivalent to each corresponding experiment; although 60cm is my worst voltage result and 10cm is my worst resistance result as they have the largest ranges between them, I go exactly the same current reading for each repeat. Also, I have taken all my results to two decimal places and conducted each experiment twice to find an average, making my experiment as accurate as possible.
Although I have conducted my experiment to the highest degree of accuracy possible within my resources, there are still a number of errors and difficulties I came across.
When measuring the wire with a metre ruler, I found it difficult as the wire was unstable and therefore some wire lengths might not be accurate. To overcome this problem, in future experiments, the wire could be stuck onto the metre ruler.
The voltmeter also fluctuated, which would have affected the results but nothing can be done for this as voltmeters fluctuate in whatever experiment is being conducted.
The wires also heated up during the experiment, which affected the experiment because the atoms in the wire will vibrate more, increasing the amount of collisions. To solve this problem, I could have used a lower voltage such as 1V or cut different wires for each experiment, but this is obviously inappropriate, as it would mean wasting more wire.
Finally, when handling the wire, such as when stretching it out, extra voltage would have been added as humans have internal voltages.
If I conduct this experiment again, I will trial different thicknesses of wire and different materials to increase my knowledge of resistance:
Diameter:
To learn how diameter affects resistance, I shall change the diameter of each wire but I will control the length, material and temperature to make my experiment fair. For this set of experiments I predict that as the diameter increases, the resistance will decrease because there will be more atoms and therefore more gaps and opportunities for the electrons to pass through.
Material:
To learn more about how material affects resistance in wires, I will use a different type of material for each experiment but I shall keep the length, diameter and temperature the same. The outcome will depend on the atomic structure of each material; some will have small atoms with large gaps, whereas others may have large atoms with small gaps, altering how quickly or slowly an electron can pass through, furthermore altering resistance.
Temperature:
When I come to learn more about temperature I shall control the temperature by using a water-bath with temperatures at a range of 30°C to 60°C, but I will keep the length, diameter and material the same throughout this set of experiments to make it fair. I predict the outcome for this experiment will be that as the temperature increases, atoms will be given more energy to vibrate more and so more collisions will occur, increasing resistance.
I could have also used a multimeter in place of the voltmeter and ammeter. This would have made conducting my experiment much easier as the device works the resistance out for you instead of going to the trouble of using to separate devices and making calculations.
It may also have been a better idea to have used a rheostat in place of the bulb because it will not heat up and change the resistance of the wire like a bulb as it is simply a long coil of wire.
