Investigating the Factors Which Have Impacts on the Resistance of a Wire
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Introduction /Background information:
The electrical resistance of a circuit component or device is defined
as the ratio of the voltage (electric potential energy per unit
charge, measured in joules per coulomb = V) applied to the electric
current (the rate of charge flow past a given point in an electric
circuit, measured in coulombs/second or Amps = A) which flows through
Resistance = Voltage / Current
If the resistance is constant over a considerable range of voltage,
then Ohm's law which states that: The electric current which flows
through many conductors (devices designed to transmit electricity,
heat, etc.) of electricity is directly proportional to the voltage
applied to them; I = V/R, can be used to predict the behavior of the
Whether or not a material obeys Ohm's law, its resistance can be
described in terms of its bulk resistivity (the electrical resistance
of a substance of a standard length and cross section). Thus the
resistance is temperature dependent. This temperature dependence can
be predicted from the fractional change of the resistance in Ohms.
Before starting my experiment I have decided to choose a factor that
will affect the resistance of a wire.
I shall do this by going through all of the factors that affect the
resistance of a wire and reasons why they affect the resistance of a
wire. From this list of factors I shall only pick one factor to
investigate and that will be the length of the copper wire.
- The material of the wire. (What the wire is made out of):
The type of material will affect the amount of free electrons which
are able to flow through the wire. The number of electrons depends on
the amount of electrons in the outer energy shell of the atoms, so if
there are more or larger atoms then there must be more electrons
available. If the material has a high number of atoms there will be
high number of electrons causing a lower resistance because of the
increase in the number of electrons. Also if the atoms in the material
are closely packed then the electrons will have more frequent
collisions and the resistance will increase. In this experiment I am
going to use copper wire which bends easily and is a good conductor of
electricity and heat.
- The length of the wire:
This is because when you have a long wire, the electrons have to
squeeze together for longer to be able to pass through the wire
than they do in order to be able to pass through a short wire. I
predict that the longer the wire, the greater the resistance so if the
length is doubled the resistance should also double. This is because
if the length is doubled the numbers of atoms will also double
resulting in twice the number of collisions slowing the electrons down
and increasing the resistance. My graph should show that the length
is proportional to the resistance
- The thickness of the wire. (The diameter of the wire)
In a thin wire these electrons have to squeeze tightly together in
order to pass through, however in a thick wire these electrons do not
have to squeeze together as much to be able to pass through. So the
more they squeeze together, the higher the resistance.
- 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.
To chose which factor I am going to investigate I am going to consider
how I would measure each factor and which factor would be the best and
easiest to record.
To measure the wire diameter I would use different widths of the same
length and same material of wire e.g. thin, medium and thick copper
wire with thin and thick constantan wire. To record the difference in
widths I would use the same voltage and measure the resistance for
each thickness. Although it would be easy to obtain and record the
data the graphs that I would be able to draw up would not be
interesting. For the temperature of the wire I would not be able to
carry out a fair test because it is extremely difficult to produce and
control the range of temperatures needed without the correct
equipment. If I chose to measure the difference in the resistance in
different materials I would chose a number of different materials and
using the same voltage I would record the resistance given by each
wire of the same length and width. Although once again it would be
simple to record these results the graphs that could be drawn would
not show any connection between the material and the resistance
because of the limited number of materials I could test with the
equipment available. The final factor is the length of the wire. To
measure and record the findings for this factor would be simple and
the results collected could show a connection between the length of
the wire and the resistance given by the wire. This is why I have
chosen to investigate this factor.
Resistance is a force which opposes the flow of an electric current
around a circuit so that energy is required to push the charged
particles around the circuit. The circuit itself can resist the flow
of particles if the wires are either very thin or very long.
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 4 volts at a constant room temperature, the same width of material
(Copper) and the length being the only variable throughout the
- Copper Wire
- Meter ruler to measure the copper wire being tested to ensure a fair
- Power Supply to transmit electricity to Voltmeter and Ammeter.
- Voltmeter & Ammeter to measure the resistance.
- Crocodile clips to connect the wire being investigated to the rest
of the circuit.
- Wires to connect the above items and to complete the circuit.
1. Collect apparatus:
2. Set apparatus up as shown:
3. Set the power pack on a constant 4 voltage. (So that there is not
too high a current passing through the circuit.)
4. Place the 10cm copper between the two crocodile clips to complete
5. Turn on the power pack and record what the ammeter and voltmeter
6. Replace the 10 cm of wire with the 20 cm of Copper wire
remembering to keep the voltage the same. Turn on power pack and
record what the ammeter and voltmeter say.
7. Repeat the experiment till up to 80cm.
8. Work out the resistance for all the results using Ohm's law.
9. Record results in a table.
10. represent table data in graph
Length of Copper Wire (cm)
Average of 3 Trials Voltage Output
Average of 3 Trials
From these results I have drawn a graph of the length of the wire and
the resistance of the wire:
* The graphs which compare the length of the wire to the resistance
it travels in a straight line through the origin. This means that
the size of the length is directly proportional to the resistance
it gives. I can work out the gradient of this line by dividing the
height of the line by the width.
* The results for the copper wire have a pattern to them. The result
for 40 cm is 2.00, and the result for 40 cm is 4.01, so I can
predict that the result for 120 cm will go 6.00 and so on.
* As the flow of current decreases, the length of the wire
My hypothesis was correct because the length of the wire affects the
resistance of the wire, the longer the wire the higher the resistance
because the number of atoms in the wire increases or decreases as the
length of the wire increases or decreases in proportion.
Ohm's law states that the current flowing through the circuit is
directly proportional to the voltage applied. (If you double one, you
double the other.)
I worked out the resistance of the wires by using the formula:
V/I = R or v = I x R
This happens because of the electrons that flow through the wire.
These electrons travel at a steady pace, while moving through the
wire, the electrons need to squeeze together. This is because there is
not enough room/space for them to pass evenly through. The more the
electrons have to bump together then the higher the resistance; as it
will take longer for them to pass from one side of the wire to the
other side. This is because the current is slowed down. (The longer
the wire, the longer the electrons have to stay squashed together, and
so the longer they take to pass through the wire and the higher the
There were a very few faults in my results as the resistance of a
double of a certain length wasnÂ’t always double the exact resistance.
This could have been because the wires were not exactly the correct
length or because I did not read the voltmeter and ammeter accurately.
The wires might have been over-heated as the temperature of the wire
will affect the resistance. Hotter wires will have a higher resistance
than cold wires.
To improve my results I should have obtained more than three results
for each wire length.
The 4 Volts Power input from the supply would have been varied, so as
to found out if it by any means have a dramatic effect on the
resistance of the wire. I should have expanded my experiment by
investigating on longer lengths of the copper wire so as to see if the
path of the resistance could have been altered by very much longer
During my experiment I have noticed several modifications I could make
to improve on the Investigation if I was to repeat it.
Some of these modifications would be:
-To acquire a more reliable circuit that I would use so as to be
accurate with my results.
-Instead of connecting the voltmeter to the main circuit I would
connect it to the wire which 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.
As well as making these modifications I would also improve my
Investigation by testing the same wire but different widths of that
wire not only the length.