1.Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their
increase in energy. This causes more collisions between the electrons and the atoms as
the atoms are moving into the path of the electrons. This increase in collisions means that
there will be an increase in resistance.
2.Material: The type of material will affect the amount of free electrons, which are able to flow through
the wire. If the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.
3.Wire length: If the length of the wire is increased then the resistance will also increase as the
electrons will have a longer distance to travel and so more collisions will occur.
The length increase should be proportional to the resistance increase.
4.Wire width: If the wires width is increased the resistance will decrease. This is because of the
increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.
I predict that if the length increases then the resistance will also increase in proportion to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to
collide with the atoms. So if the length is doubled the resistance should also double.
This can easily be shown in everyday life. If you have a long corridor there is more chance of less people colliding than in a very small corridor.
We will be keeping everything in the experiment the same the whole way through (battery pack, voltmeter, ammeter, wires etc.) however the only thing we will change is the length of wire being tested. This is done so the test is a ‘fair test’ and there is no bias involved.
Once I have preformed my experiment I will use graphs and tables to try and see if my prediction was correct.
Points of Safety
- Always avoid switching on/off the power supply with wet hands.
- Allow the wire to cool in-between experiments.
- Ensure the power supply is switched off before you make any alterations to the circuit.
- In an emergency, use the on/off switch on the power supply its self to break the circuit.
- Do not leave the circuit unattended when the power supply is switched on.
- Do not leave the power supply on for long lengths of time.
Fair Test Points
- Make sure that the voltage coming from the power supply is kept constant throughout the experiment.
- Maintain the same current (0.3A) throughout the experiment.
- Use the same wire to prevent unwanted variations, for example altering width or density.
- Repeat the experiments and find the average to obtain more accurate results.
- Use mounted bulldog clips to give the experiment a secure and static base, and to prevent unwanted movement
- Switch off the power supply and allow the wire to cool in-between experiments, to prevent any initial resistance.
- Use the same equipment, particularly the same ammeter and voltmeter, as others don’t always share the same resistance.
- Make sure all experiments are carried out under the same temperature conditions, for example on the same day, as an increase in temperature, increases resistance.
- Add an extra 1cm onto the length of the wire to ensure that there is 0.5cm on each end for the bulldog clips to sit. This reduces error.
-
Use a current of 0.3A, as this will cause minimal heat and resistance to the wire.
What I will need for this experiment.
A power supply - Battery
Ammeter – to find the Current (Measured in ampere)
Voltmeter – to find the Voltage (Measured in Volts)
Crocodile clips – To attach the sample wire to
Wire – To complete the circuit and move the power around the circuit.
Meter ruler – to measure my lengths of wire.
I will set all this up like this.
The piece of wire being tested will be CONSTANTAN 125g 0.91mm
Once we have carried out our experiment I will place my results in a table and prepare to start analysing it and making graphs and chart.
I will make a table like this to place my results in.
To collect the data for my graph I have chosen to take a range of 10 lengths. I have chosen a range of 10 lengths as to plot an accurate graph I will need at least 5 points to mark on the graph. I have also chosen to take 2 repeats at each length and then take an average. I have chosen this so that if I have any anomalous results they will not show when I plot the averages on the graph. The lengths that I have chosen are as follows: 10cm 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm and 100cm. I have chosen these lengths because
They are easily measured by the meter ruler and give a good range.
I will place my results in a graph. Here is the axis I will use for the graph.
The points on my graph of experiment one are a little scattered, but the line of best fit is a straight line which does go through the origin, which means the resistance is directly proportional to the length. So if the length is 50cm, and resistance is 1ohms, when the length doubles to 100cm, the resistance also roughly doubles to 2.01ohms. There was also a few anomalous points, 0.1ohms and 1.65ohms. I probably did not read the results accurate. My graph proves ohms law, that the voltage is proportional to the current (if temperature is kept constant). This agrees with my original hypothesis that doubling the length of wire ought to make it twice as difficult to push electrons through.
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 in proportion.
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, which 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.
My results are not completely accurate for many reasons:
The temperature of the wire will rise which will affect the resistance. The temperature will increase because when there is a current flowing through a resistance, this will cause the atoms in the wire to vibrate, stopping the flow of electrons therefore the resistance will increase. I could of over came this by putting the wire in a beaker of cold water.
When measuring the lengths of the wire the length might not be accurate as the wire might not be completely straight.
There could have been a different thickness in the length of wire.
Even though of all these problems my results are still accurate enough to support my prediction. If I did this experiment again, I would use newer, with a more sensitive range ammeters and voltmeters, a more accurate way of measuring, and I would take a wider range of readings, and more readings so I could get a more accurate average. I would also investigate other factors such as, temperature, voltage and type of wire, to see how these affect the resistance.
To help me with this investigation I used the following:
Complete Physics by Stephen Dople
Letts GCSE Physics
CGP Physics by Richard Parsons
Encyclopaedia – Britannica 99 CD-Rom