The unit of resistance is Ohms and the symbol is: Ω
The higher the resistance, the lower the current. If there is high resistance, to get the same current a higher voltage will be needed to provide an extra push for the electricity.
Some metals have less resistance than others. Wires are always made out of copper because copper has a low resistance and therefore it is a good conductor. The length and width of a wire also has an effect.
Predictions:
I predict that the longer the piece of wire, the greater the resistance will be.
This is due to the idea of the free moving electrons being resisted by the atoms in the wire. In a longer piece of wire, there would be more atoms for the electrons to collide with and so the resistance would be greater.
The relationship between the wire length and the resistance should be directly proportional.
I think this because, as I have explained above in my preliminary work, the longer the wire the more atoms and so the more likely the electrons are going to collide with the atoms.
An example of this would be in a 20cm wire. The electrons would have to travel double the distance than it has to go through a 10cm wire. This would in turn double the amount of atoms that the electrons would collide with and therefore the resistance would be double.
Fair Test:
To ensure that the investigation is carried out in a fair way and that the results will be accurate and reliable a number of things must be followed. The only variable in the test will be the length of the wire. The wire must be pulled tight against the ruler and taped in place to ensure the length is accurately measured. The surrounding temperature must be constant, or near enough constant, so the experiment should only be done on one day this is because if the temperature of the room is hot enough the free electrons in the wire could pick up energy that would make them move faster and consequently the resistance of the wire could be affected. The experiment should be repeated 3 times and an average taken to make sure that the results are reliable.
Equipment:
The apparatus I will need to carry this investigation out is:
Constantan wire Meter Ruler - to accurately measure the length of the Constantan wire. Multimeter - to accurately measure the resistance in the wire.
Wire clippers - to safely cut the wire to length. Crocodile clips – to connect the Multimeter with the wire.
Method:
1. Gather up listed equipment.
2. Take reel of constantan wire and use meter stick and wire clippers to measure and cut 100cm (1m). Make sure wire is taught and stick to the ruler with tape on both ends.
3. Place one crocodile clip on 0cm and the other on 10cm.
4. Measure the resistance using the Multimeter. Record reading.
5. Keeping the first crocodile clip on 0cm move the other crocodile clip onto 20cm and try to keep a steady hand when holding them in place.
6. Repeat step 5 for 30cm and repeat until you have measured the resistance for 100cm.
Diagram:
The diagram shows what your equipment should look like once you have set it up.
Safety:
Be careful when cutting the wire and make sure your desktop is clean and tidy to avoid confusion. Be careful, as you will be using expensive equipment such as the Multimeter.
Results:
Analysis:
The results from the graph give a clear indication of how the resistance compares to the wire length. There is a very strong positive correlation. This means that when the length of the wire increases, the resistance also increases. The results are also directly proportional, meaning that when one doubles so does the other. An example would be at a wire length of 50 cm, the resistance is 5.1Ohms and at 100 cm it is 9.5Ohms. This is almost double the resistance.
The theory behind this is explained in my prediction. In any given metal wire, there are a number of atoms and free moving electrons. Electricity is the movement of these electrons through the wire. Resistance is caused when the free electrons moving through the wire collide with the atoms making their path through the wire becomes more difficult. This means that if there are more atoms in the way to collide with the free electrons the resistance is increased. In a length of wire there will be a number of atoms, and in a wire twice the length, there will be twice the number of atoms. In turn this will lead to there being double the number of collisions between the electrons and the atoms increasing the resistance by 2. This explains why the results were directly proportional. For example a wire that was 10 cm long may have 500 atoms blocking the electrons. Therefore in a wire 20 cm long, there would be 1000 atoms meaning that the resistance had doubled.
The results that I have obtained support my original prediction. This is because in the prediction I said that as the wire length increased, the resistance should increase. I also said that the link should be directly proportional. The results have shown that this is true in most cases.
The line of best fit clearly shows that the results followed the expected pattern very well. The points are very close if not touching the line. This shows how the results were directly proportional through out, as the gradient remained the same.
Evaluation:
Overall, my experiment worked very well. The method that I used in the practical was efficient and my results were reliable. After studying my results, I realized that there are some anomalous results. My first anomaly is at 10 cm when the resistance recorded was 1.5Ω, the second at 20cm with a 2.5Ω resistance and a third was at 30cm where I recorded a 3.5Ω resistance. These anomalous results didn't alter the increasing pattern in resistance. I think that I got some anomalies because it was hard to keep a steady hand when I connected the Multimeter to the wire, this would therefore mean that the connection would not be directly on the correct measurement.
I think all of my other results were accurate and followed the patterns I predicted previously. In my analysis, I mentioned a theory about the resistance doubling as the length did. This would occur because if the area of the wire doubles, so does the number of possible routes for the current to flow down. Therefore, the energy is twice as spread out, so resistance might half.
The method I chose to use was very suitable. Following the fair test criteria ensured that my results were accurate, and the experiment was completed appropriately. However, minimal changes could have been made in order to improve the reliability of my evidence.
Measuring the lengths of the wire is an inaccuracy the rulers may not be exact. As some were old, some measurements may have been scratched off. It is difficult to get an accurate reading of length by eye, as the wire may not be completely straight.
A factor that perhaps reduced the degree of accuracy was the connection of crocodile clips. They may not have always been connected to the constantan wire securely and at the correct length. This meant they could have been free to move, altering the length of wire and therefore my results wouldn’t be very accurate.
I can prove that my experiment was successful because of the graph I drew, it showed length of wire against resistance.
I don't think that by doing any more results in my experiment would improve the accuracy at all. I took three readings each of the resistance and also worked out an average, which I used to work out the resistance.
The only way to make the results more accurate would be to use a different method. Perhaps I could use a metal bar in place of the wire. This way, I could still investigate the length of wire affecting resistance, but more accurately. A disadvantage of this would be that the attachment of the crocodile clips would be less secure depending on the width and thickness of the wire.
If I had the chance to do the experiment again, I would investigate other factors. Examples of these are temperature, voltage or current. I would see how these additional factors affect the resistance in the wire.
