Electricity in the Home.
Method
For my test, I have chosen to take a range of 5 lengths. I have chosen a range of 5 so that I can plot an accurate graph. I have also chosen to repeat each test 3 times and then make an average for each length. I will do this so if I get any anomalous results then they will not be noticed when I plot the graph. I have chosen the lengths : 0cm , 15cm , 30cm , 45cm and 60cm. I chose these lengths because the ruler can easily measure them and they have a good range. I will use an ammeter and voltmeter and calculate the resistance of the wire. To work out the resistance of the wire I will use the equation below.
R = (rl)/A , where R = resistance
r = resistivity
l = length of wire
Range.
The amount of Voltage I will be using will be 6V
The amount of current I will be using will be 1.1A
Apparatus.
Power Supply.
Ammeter.
Voltmeter.
Wire.
Meter Ruler.
Crocodile Clips.
Connecting Wires.
Variable Factors.
Wire width.
If the width of the wire is made bigger, the resistance will decrease. This is due to an increase in room for the electrons to travel through. Due to this extra space between the atoms, there should be fewer collisions and therefore a lower resistance.
Wire length.
If the wire is made longer then the resistance will also be more because the electrons will have further to travel and so there will be more collisions.
Material.
The type of material will affect how many free electrons are able to flow through the wire. If there are a lot of atoms in the material then there will be a lot of electrons creating a lower resistance. If the atoms in the material are more tightly packed, then the electrons will have more collisions and the resistance will be bigger.
Temperature.
If the wire is gets hot then the atoms in the wire will begin to vibrate because they will now have more energy. This creates more collisions between the electrons and the atoms. More collisions means more resistance.
Diagram.
Obtaining Evidence.
Analysing My Graph.
By looking at my graph on the previous page, you can see how the resistance of the wire is proportional to its length. I know this because the Line of Best Fit is a straight line showing that if the length of the wire is increased then the resistance of the wire will also increase.
I predicted that if the length increases than the resistance will also increase with proportion to the length. From my graph, I have shown that my prediction was correct, because the Line of Best Fit is a straight line proving that the resistance of the wire is proportional to the length of the wire.
The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases. The resistance of a wire depends on the number of collisions the electrons have with the atoms, so if there are more atoms then there will be more collisions, which will increase the resistance of the wire.
Evaluation.
Anomalous Results.
I believe that the reason one of my results was not on the line of best fit was due to ohmic heating in the wire because the current was left running too long. If the wire is gets hot then the atoms in the wire will begin to vibrate because they will now have more energy. This creates more collisions between the electrons and the atoms. More collisions means more resistance.
Conclusion.
The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material , so if there is a larger number of atoms there will be a larger number of collisions that will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased, the number of atoms will also increase, giving a greater resistance.
Improvements.
If I were to do this experiment again then I would ensure that lengths and thicknesses were measured more accurately to make it a better test. Another good method of improving my results would be to do it in a temperature-controlled environment. A good method of doing this would be to have cool air constantly blown over the test in order to keep it at the same heat.
Taking more readings and of a wider range would also help me to gain a better average. These alterations would probably give me better results, and possibly remove my anomalous result.
To expand on my experiment I would test the same wire but different widths of that wire to see if I got the same results then, this would further prove this theory.