Method
First of all I will get a 12V power pack and some wire. Next I will need is an ammeter
and a voltmeter and a variable resistor. I will fist connect the power pack to the mains and
making sure my hands are not wet, so I don't get an electric shock. Next I will connect
one of the wires to the negative end of the power pack and connect the other end of the
wire to a variable resistor. Afterwards I will get a second wire and connect it to the
unconnected terminal of the variable resistor and add a crocodile clip to the unplug end of
the second wire. This crocodile clip is to hold the wire in place and to connect it to the
circuit. From the positive terminal of the power pack a wire will be connected to the
terminal and also the ammeter. The fourth wire is needed to connect the unconnected
terminal of the ammeter and like the second wire a crocodile clip will be added to
connect the wire. Behind each end of the crocodile clipped wires they should be other
wires connected to the voltmeter, making a parallel circuit. This is because in a parallel
circuit the voltage is always the same in each circuit made, whereas if we connected the
voltmeter in a series the voltage measured would vary depending on which side it is
connected. Picture of this set up is on the diagram section.
Once that is done we need to measure each wire (constantan wire) the length of 80
cm because from my preliminary experiment that was carried out 80 cm wasn't very hot
and gave good readings. Below is a table with the results: Length (cm)
100
80
60
40
20
SWG
21
21
21
21
21
V/V
2
2
2
2
2
Current (amps)
0.86
2.00
2.90
3.18
6.27
Temp
Cold
Warm
Hot
Very hot
Extremely hot
When measuring the wire I must always keep the wire length 80-cm because the length of
wire can effect the resistance and give me inaccurate results. When measuring the wire
the wire must be held flat against the meter rule (We use a meter rule because it is long
enough to measure 80 cm and more accurate than longer than this length) to give a fair
result because if this isn't done more metal maybe measured and we won't get accurate
results. The wire will then be cut to 80 cm. This 80-cm wire will be placed in between the
two crocodile clip and clipped to connect it to the circuit. Turn the power on and adjust
the variable resistor. We used a variable resistor for accuracy and it can measure the
voltage very accurately rather than using the power pack because it isn't always accurate,
making this method a fair method. The resistor will be moved left and right until the
voltmeter display 1 and the voltage must be kept the same because the resistance might
vary. The reading on the ammeter is the current and must be recorded three times because
the result will be more accurate and because the ammeter always vary even kept at the
same voltage.
Wires that are tested are made out of constantan and every time a different size of wire
will be used when one is finished recording. The size used will be 21, 24, 28, 30, 34, 36,
40, 42 and 44 SWG and all will be measured to 80 cm. After testing the current of each
wire, each wire's diameter will be measured in order to work out each cross sectional
area. This will be done using a micrometer. A wire say 21 SWG is placed in the gap of
the micrometer and turns the ratchet clamping the wire until no more can be turned. The
point that lines up with the dash is read off at eye level because it is more accurate than
not eye level because a different size could be measured than the real one. I will measure
each size of wire 5 times because in the case where different parts of the wire might be
smaller than other parts, so when measuring 5 times I will measure each time in a
different part of a wire, to get a average and very accurate results.
Another safety precaution is that the wires maybe hot after testing so I will watch
that I do not burn myself.