Independent Variable
I will change the length of resistance wire
This will be done so we can see how the length of wire affects the resistance. I will use 52cm-92cms of resistance wire.
Dependant Variable
I will measure:
1. The current flowing through the circuit. The ammeter will measure this in amps.
Controlled Variable
I will keep the same:
1. 3.0v in the voltmeter
2. The thickness of the wire
3. 1cm at each end of the resistance wire for the crocodile clips. This is done so there is exactly Xcm in between therefore keeping the experiment accurate.
Apparatus:
Resistance wire
Power pack
2 crocodile clips
Voltmeter
Ammeter
Wire leads
Meter stick
Variable resistor
Method
1. Measure 92cm of resistance wire using the meter stick for the first trial and coil around a pencil making sure coils do not touch. The coils should not touch because if they did the circuit would short and make the experiment inaccurate.
2. Set up apparatus using the equipment on the previous page. Start with the powerpack, add a wire to the positive side and then connect the ammeter in series. Next, connect that wire to one side of the resistance wire using a crocodile clip. To the other side of the coil add another crocodile clip and connect to the next wire. Add a voltmeter in parallel to the resistance wire. Lastly, add the variable resistor and connect back to powerpack.
3. Get the circuit checked by a teacher
4. Using the power pack get the voltmeter to read 3.0v and record the value in the ammeter
5. Repeat two more times so you are left with three readings (turn of power pack between each reading so the wire can cool down)
6. Repeat steps 1-6 replacing 92cm with 82cm and repeat experiment reducing the amount of resistance wire by 10cm each time until 52cm is reached.
Sample Table
Length of resistance wire (cm)
Voltage
(V)
Current (amps)
Average
(Amps)
Resistance
R=VI
()
1 2 3
50
60
70
80
90
Sample Graph
Safety
1. Make sure the circuit is checked by teacher before you start experiment
2. Keep all chairs and bags under table
3. Do not let wire heat up too much.
Obtaining Evidence
Length of resistance wire (cm)
Voltage
(V)
Current (amps)
Average
(Amps)
Resistance
R=VI
()
1 2 3
50
3.0
0.95
0.95
1.00
0.97
3.1
60
3.0
0.82
0.82
0.82
0.82
3.7
70
3.0
0.70
0.70
0.70
0.70
4.3
80
3.0
0.60
0.60
0.61
0.60
4.8
90
3.0
0.54
0.54
0.54
0.54
5.6
Conclusions
I have found out that the length of resistance wire increases the resistance in the circuit
What trends and patterns can you see in your graph?
In the graph we can see that the straight line passing through the origin agrees with ohms law. We know this because in the graph it is clear to see that when the length of wire increases the value of resistance also increases, this is told by the continuous straight line. If we were to keep reducing the wire by 10cm until there was none left and finding the amount of resistance in the circuit the line of best fit should keep going straight on.
What conclusion can you come to?
The conclusion I can come to is that the length of wire definitely affects the resistance throughout the circuit i.e. the longer the wire the higher the resistance.
We know this because in the results that I obtained, whenever you increase the length of resistance wire by 10cm the value of the previous resistance also increased by either 0.5ohms or above so this is clear evidence that length effects resistance.
Length of resistance wire
(cm)
Resistance
R=VI
()
Difference
()
50 3.1
0.6
0.6
0.5
0.8
60 3.7
70 4.3
80 4.8
90 5.6
Also the total difference in the circuit between 50 and 90cm of wire is 2.5 ohms, which shows that there is a big increase when the length of wire is increased.
What conclusions can you come to?
The conclusion I can come to is that the length of resistance wire affects the value of resistance. This is because of the arrangement of the atoms in the resistance wire. The atoms are arranged so that it is much harder for the free electrons to travel through it. When the length of the wire is longer it is more difficult for the electric current to travel through the wire because there is a much greater distance of resistance wire for the current to travel through and so it takes longer therefore causing a higher resistance.
Does your conclusion support your prediction?
Yes my conclusion supports my prediction because I predicted that the longer the wire the greater the value of resistance and it is clear from my results this happens.
Are your results reliable?
I think my results are quite reliable because in the graph 3 out of the 5 points lie on the line.
There are 2 anomalies but they are only just off the line and I think they might have been caused by either:
1. Inaccurate reading of ammeter
2. Length of wire not accurate
3. Bumps in wire
4. Crocodile clips not in the right place
Could you improve your experiment in anyway?
The experiment could have been improved by using new resistance wire for each length instead of using the same piece each time because when you uncoil the wire it is not completely straight so affecting the results. Also I could have left a more accurate amount of wire for the crocodile clips to go on, as 1cm at each end could have been too long.
Are your results reliable enough to make a firm conclusion and convince others?
I think that my results are reliable enough because in the graph only 2 points lie off the line and they are very close to the line which shows there wasn’t much error so I think they would convince others.
Ashlene Clarke
