Crocodile clips - to attach the wires being used to the rest of the circuit.
Voltmeter & Ammeter - to measure the resistance.
Wires - to connect the above items and to complete the circuit.
To measure the resistance of the wire I am going to use the equation RESISTANCE=VOLTS/CURRENT I will obtain the voltage and current readings from the voltmeter and ammeter.
Below is a circuit diagram for my preliminary experiment.
POWER SUPPLY
2 VOLTS
AMMETER
VOLTMETER
CROCODILE CLIPS
WIRE
METER RULER
To ensure a fair test I shall keep the power supply at 2 volts and I shall keep the length of the wire at 50 cm.
Preliminary Results
Below is a table of results that I have collected from my preliminary experiment.
From these results, I can see that the resistance is directly proportional in the way that it increases
Main Method
Before I start my main experiment, I have chosen to do a risk assessment that is shown below.
Risk Assessment:
"I will handle the power supply carefully.
"I am going to only use a voltage of 2 volts.
"I will be careful when handling live wires.
Apparatus: Power Supply
Ammeter
Voltmeter
Nickelchrome wire
Meter Ruler
Crocodile Clips
Connecting Wires
I have chosen to use nickelchrome wire because from my preliminary results I found that this wire had the high resistance, because it has a high resistance it will be easier to measure any change.
To collect the data for my graph I have chosen to take a range of 5 lengths. I have chosen a range of 5 as to plot an accurate graph I will need at least 5 points to mark on the graph . I have also chosen to take 3 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: 20cm, 40cm, 60cm, 80cm and 100cm. I have chosen these lengths because they are easily measured by the meter ruler and give a good range.
Below is a circuit diagram of the circuit I am going to use in my main experiment:
POWER SUPPLY
2 VOLTS
AMMETER
VOLTMETER
CROCODILE CLIPS
WIRE
METER RULER
In my main experiment instead of using an ohmmeter I have chosen to use an ammeter and voltmeter, I have done this so that instead of relying on the ohmmeter to give the resistance I will calculate the resistance of the wire; I shall calculate the resistance of the wire using the equation below.
RESISTANCE = VOLTS/CURRENT
I have chosen to use a meter ruler because the lengths that I will be measuring are to big for a smaller ruler and the meter ruler can be accurate to 1mm.
Results
Below is a results table with the results that I collected from my main experiment.
From these results, I have drawn a graph of the length of the wire and the resistance of the wire. I have also drawn a graph of the wire thickness the resistance of the wire as the thickness increases.
Analysis
From the graph for the length I can see that the resistance of the wire is proportional to the length of the wire. 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. From the graph for the thickness, I can see that the resistance of the wire is inversely proportional to the thickness. I know this because the line of best fit is a curve from the top of the graph to start and at the bottom of the graph at the end of the results used. This shows that as the thickness of the wire increases, the resistance of the wire decreases.
Conclusion:
In my prediction, I said that: If the length increases than the resistance will also increase in proportion to the length. From my graphs, I have shown that my prediction was correct, as 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 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 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
Evaluation:
From my results table and graph I can see that my results that I collected are very reliable. I know this because my results table does not show any individual anomalous results this means that I did not have to leave any results out of my averages because they were anomalous. Also on the graph I can see that none of the averages plotted are anomalous because all the averages lie along the same straight line. During my experiment I have noticed several modifications I could make to improve on the Investigation if I was to repeat it: The first of these modifications would be the circuit that I would use. To be more accurate with my results I would use the circuit layout below:
POWER SUPPLY
2 VOLTS
AMMETER
VOLTMETER
WIRE
METRE RULER
Instead of connecting the voltmeter to the main circuit I would connect it to the wire that is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well. To also improve on my results I would use a digital voltmeter instead of an analogue meter. I would do this because a digital voltmeter is a lot more accurate than an analogue because if the needle in the analogue voltmeter is bent then the readings given off will be false whereas a digital voltmeter does not rely on a needle or any other manual movements. The next modification I would make would be to use pointers instead of crocodile clips; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire. As well as making these modifications, I would also improve my Investigation by testing the same wire but different widths of that wire. I would do this to expand on my Investigation.
