be half the number
of collisions between the electrons and the atoms.
The wire below is twice the length of the wire above and so there should be twice the number of atoms
resulting in twice as many collisions and a predicted doubling of the resistance.
Preliminary Method
In this preliminary experiment I will select a wire that will be used in my main experiment when
investing the connecting between the length of the wire and the resistance of the wire.
To ensure a fair test whilst carrying out my preliminary experiments I am going to be very careful
when selecting my independent variables which are the width of the wire and the wire material. I am
going to use a constant voltage of 2 volts and a constant length of 50 cm.
Apparatus: Meter ruler ¡V To measure the wire being tested to ensure a fair test.
Selection of wires ¡V Different materials and widths but the same length.
Crocodile clips ¡V To connect the wire being investigated to the rest of the circuit.
Voltmeter & Ammeter ¡V To measure the resistance.
Wires ¡V 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 which I have collected from my preliminary experiment.
WIRE VOLTS (v) AMPS (A) RESISTANCE (Ohms)
THICK COPPER 0.3 5.13 0.06
MEDIUM COPPER 0.6 4.20 0.14
THIN COPPER 0.9 3.13 0.29
STEEL 0.7 1.20 0.58
MEDIUM CONSTANTIN 1.0 0.41 2.44
THIN CONSTANTIN 2.7 0.49 5.51
From these results I have chosen to use thin constantin for the wire I am going to use in my main
experiment. I have chosen this wire as it has the highest resistance and so it will be easier to notice any
difference in resistance in my main experiment
Main Method
Before I start my main experiment I have chosen to do a risk assessment which is shown below.
Risk Assessment:
„h I will handle the power supply carefully.
„h I am going to only use a voltage of 2 volts.
„h I will be careful when handling live wires.
Apparatus: Power Supply
Ammeter
Voltmeter
Thin Constantin wire
Meter Ruler
Crocodile Clips
Connecting Wires
I have chosen to use thin constantin wire because from my preliminary results I found that this wire had the highest resistance, because it has the highest resistance it will be easier to measure any change in resistance.
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
AMPS
I have chosen to use a meter ruler because the lengths that I will be measuring are to big for a smaller
ruler and also the meter ruler can be accurate to +1mm or ¡V1mm.
Results
Below is a results table with the results that I collected from my main experiment.
LENGTH 200 mm 400 mm 600 mm 800 mm 1000 mm
VOLTS (v) 1.6 1.5 1.6 1.7 1.7 1.7 1.8 1.8 1.8 1.9
1.8 1.8 1.9 1.9
1.9
AMPS (I) 0.608 0.609 0.607 0.351 0.352 0.351 0.237 0.238 0.238 0.184 0.184 0.184 0.148 0.149 0.149
RESISTANCE
(Ohms) 2.6 2.5 2.6 4.8 4.8 4.8 7.6 7.6 7.6 10.3 9.8 9.8 12.8 12.8 12.8
AVERAGE
RESISTANCE
(Ohms)
2.6
4.8
7.6
10.0
12.8
From these results I have drawn a graph of the length of the wire and the resistance of the wire.
Analysis
From the graph on the previous page 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.
Conclusion
In my prediction I said that :
¡§¡K.if the length increases than the resistance will also increase in proportion to the length.¡¨
From my graph 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 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. This is shown in my diagrams below:
Electron
Atom
In this 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
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.
1. I will measure the resistance of 8 different lengths of nickel-chrome wire using the ammeter-voltmeter method.
2. For the first length, which will be 10cm, I will measure the current going through the wire and then I will measure the voltage across the 10cm of wire.
3. I will then find the resistance of the wire using Ohm’s Law, where I will have to divide the obtained voltage by the current reading to get the resistance.
4. I will repeat the above process for all the lengths of wire, ranging from 10cm to 80cm.
5. I will repeat the whole process to prevent any errors. I will take all the readings again staring this time at 80cm and working my way back.
6. Because I will have two measurements for the resistance of each length of wire, I will find the average of these two readings.
7. I will record all the results in a table like the one below.
8. I will use a multimeter as an Ohmmeter just to check the resistance in case of any miscalculation.
SAFETY
I will ensure that none of the wires are frayed and that there is no water near any electric equipment; as in all electrical experiments.
HANDLING RESULTS
I will draw a graph of Resistance against Length of wire with Resistance on the Y-axis and Length on the X-axis,
Resistance (Ω)
If my prediction is right,
The graph should show a
Straight line through the origin.
Length (m)
AT THIS POINT IN MY INVESTIGATION I CARRIED OUT THE EXPERIMENT
METHOD
1. I set up the equipment as shown below.
2. I connected the multimeter in series with a D.C. power supply, setting the value to 4V. The multimeter was better to use because of the larger currents and because the readings are given to 2 decimal places.
3. I connected a one metre length of nickel-chrome wire which was taped a metre ruler to he output from the ammeter.
4. I then connected the voltmeter across the wire I was testing.
5. I connected the negative terminal of the voltmeter to the negative terminal of the power supply, therefore completing the circuit.
6. 10 cm of wire were stepped off by the voltmeter leads and I recorded the readings of voltage and current.
7. I repeated the above process from 10cm to 80cm in steps of 10
8. Because the shorter lengths of wire became quite hot, the readings were taken quickly, but I allowed the wire to cool down before the next reading.
9. I repeated the whole experiment again, this time starting off at the 80cm mark and working my way back to 10cm in steps of 10cm.
10. I then checked my readings with the multimeter we used in the experiment as an Ohmmeter. I recorded the resistances for each length of wire after the wire had been disconnected from the circuit.
