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Experiment to Discover How Factors Affect Resistance in Wire

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Experiment to Discover How Factors Affect Resistance in Wire

Aim

To investigate how the length of wire affects its resistance.

Hypothesis

I predict that as the length of wire increases, the resistance will
also increase. This is because current is the flow of electrons in a
circuit and voltage is the push which makes the electrons flow through
the circuit. Resistance is caused by components in circuits which slow
the flow of electrons down as it is harder for them to flow through
the circuit. There is resistance in wire and as the electrons have
further to travel through longer lengths of wire they face more
resistance, therefore the longer a piece of wire is, the higher the
resistance will be. The greater the resistance, the more voltage is
needed to push a current through the wire. The resistance of a wire is
calculated by the formula Resistance = Voltage/Current, which is known
as Ohm’s law.

Plan

An experiment will be carried out in order to discover how factors
affect resistance. Therefore variables that can affect resistance must
be considered: they include temperature, voltage, current, the length
of the wire, the diameter of the wire and what type of metal the wire
is made of. The resistance of the wire will be calculated by taking
the readings of the voltage and current through the wire for each
result. Each set of results will be recorded on a Voltage/Current
graph and the gradient will be used to discover the resistance of the
wire, as the temperature is constant (on the graphs) and will
therefore not affect the results. There will be two independent
variables: the length of the wire and a variable resistor, used to
alter the voltage across the wire. Length is the chosen independent
variable because it is easier to measure accurately than diameter.
Length of wire is easier to alter than it is to find wires of the same
length and diameter but of different materials. Temperature throughout
the wire would be difficult to measure accurately and varying the
length is safer than voltage because if a short piece of wire was used
with a high voltage, it would melt. The dependent variable that is
calculated will be the resistance, and this will be calculated by
measuring the voltage and current of the wire, at different lengths.
For each length of wire the voltage (the second independent variable)
will also vary and the current will be measured at each voltage using
an ammeter. Readings of the results will be taken using a voltmeter
and an ammeter. A preliminary experiment will be carried out to
determine the number of results taken in the actual experiment.

In the preliminary experiment, equipment was set up using a power
pack, a metre of wire, attached to other wires using crocodile clips,
and a variable resistor. A voltmeter and an ammeter were also in the
circuit to measure the results.

Preliminary results:

Length of wire

voltage

current

Resistance

1m

1.22

1.79

3.18

0.18

0.76

0.46

6.78

6.88

6.913

30cm

0.47

0.85

0.88

0.24

0.43

1.55

1.96

1.97

1.86

From the preliminary experiment it was decided that the readings will
be taken at 8 different lengths, each 10cm apart, ranging from 30cm to
1m. The variable resistor will also change the voltage through the
wire 7 times at each length.

Equipment:

* Power pack

* Ammeter

* Voltmeter

* Variable resistor (rheostat)

* Masking tape

* 2 crocodile clips

* Metre ruler

* 6 wires

* 1m Nichrome wire

Method:

Equipment was set up as in the diagram below.

A power pack was plugged into the main power supply and 4 wires were
used to create a circuit with an ammeter, voltmeter, variable
resistor, and 2 other wires were used to attach the length of nichrome
wire with crocodile clips to the circuit. The length of wire was a
metre long and this was verified by the fact that it was attached to
the metre ruler at both ends, using masking tape, which also kept the
length of wire straight. The power pack was then turned on at 4 volts.
The variable resistor was used to increase the voltage by 0.2 volts
several times, starting at 0.4 volts until 1.6 volts was reached. Each
time the voltage was altered the voltage and current were measured and
recorded, and seven readings were eventually taken. A crocodile clip
was the moved 10cm along the wire and another five readings at
different voltages were taken. This was repeated until there were six
results for lengths of wire, ranging from 50cm to 1m long, at 10cm
intervals. For each different length of wire, readings taken at 7
different voltages varied by the rheostat from a range of 0.4 volts to
1.6 volts, with a difference of 0.2 volts between each reading.
Readings were also taken with the wire at lengths of 40cm and 30cm
long, however for these results, the voltage of the power pack was
reduced from 4 volts to 2 volts for and the seven readings were taken
at a range of 0.2 volts to 0.8 volts, with a difference of 0.1 volts
between each reading. These small voltages were chosen in order to
prevent the voltage from being too high and melting the wire. Overall,
there were eight different results, each with seven readings. To keep
the results accurate, the experiment was performed in a single room,
on the same day and the resistance was calculated on a graph, so that
it was not affected by temperature.

Safety Precautions:

Caution was taken in this experiment, to prevent harm to the
surrounding area of the experiment and of those performing the
experiment. The voltage through the circuit was kept low in order to
prevent the wire from growing too hot and melting. Time was also taken
between taking each reading, when the power was turned off to allow
the wire to cool down, preventing temperature from affecting the
experiment. The fact that the results were also recorded on a graph,
also made them accurate. The length of wire was not changed by cutting
it, which could be dangerous, but by moving a crocodile clip along the
wire. While doing this, the wire was also not just touched, just the
ruler and plastic covered part of the crocodile clip.

Obtaining

Overall, a sufficient number of readings were taken, as eight results
were taken, each with seven readings, so 56 readings were recorded in
all. The results were kept accurate by taking several readings,
leaving a couple of minutes inbetween each one so that the temperature
of the wire did not increase and affect the results. The results do
follow the expected pattern, as length of the wire increases so does
the resistance. Unlike some experiments, the results were not repeated
3 times in order to obtain more accurate results, because for each
result seven readings were taken at different voltages.

Results:

The results are shown in the following tables and have been plotted on
graphs.

Readings taken at 1m length of wire

Voltage (volts)

Current (amps)

0.4

0.06

0.6

0.08

0.8

0.12

1

0.15

1.2

0.17

1.4

0.2

1.6

0.23

Readings taken at 90cm length of wire

Voltage (volts)

Current (amps)

0.4

0.06

0.6

0.09

0.8

0.13

1

0.16

1.2

0.19

1.4

0.22

1.6

0.26

Readings taken at 80cm length of wire

Voltage (volts)

Current (amps)

0.4

0.07

0.6

0.10

0.8

0.14

1

0.18

1.2

0.22

1.4

0.25

1.6

0.29

Readings taken at 70cm length of wire

Voltage (volts)

Current (amps)

0.4

0.08

0.6

0.12

0.8

0.16

1

0.21

1.2

0.25

1.4

0.29

1.6

0.33

Readings taken at 60cm length of wire

Voltage (volts)

Current (amps)

0.4

0.10

0.6

0.14

0.8

0.19

1

0.24

1.2

0.29

1.4

0.34

1.6

0.39

Readings taken at 50cm length of wire

Voltage (volts)

Current (amps)

0.4

0.11

0.6

0.18

0.8

0.23

1

0.29

1.2

0.35

1.4

0.41

1.6

0.47

Readings taken at 40cm length of wire

Voltage (volts)

Current (amps)

0.2

0.07

0.3

0.11

0.4

0.15

0.5

0.18

0.6

0.22

0.7

0.26

0.8

0.29

Readings taken at 30cm length of wire

Voltage (volts)

Current (amps)

0.2

0.10

0.3

0.15

0.4

0.20

0.5

0.25

0.6

0.30

0.7

0.35

0.8

0.40

After the results were plotted on the graphs, the graphs were used to
calculate the resistance of the wire at different lengths. These
overall results are shown below:

Length of wire (cm)

Resistance of wire (ohms)

30

2

40

2.7

50

4.1

60

4.2

70

4.6

80

5.6

90

6.4

100

6.7

Analysis

The results that were plotted on the voltage/current graphs did not
show any anomalous points, therefore, they fairly reliable. The final
graph shows the relationship between the length of wire and the
resistance of the wire. On this graph there is one point which is
slightly anomalous, however there is strong positive correlation
between the length of wire and the resistance of the wire. In
conclusion, the results show that the hypothesis was correct and
resistance increases as the length of the wire increases. The
relationship between the two axes is directly proportional. This can
be seen as the lines of best fit on the graphs are straight and go
through the origin. The relationship should be directly proportional
because current is the flow of electrons. Resistance is caused by the
flow of electrons being halted as the electrons bump into atoms on the
wire. In a shorter piece of wire, there are fewer atoms for the
electrons to collide with and so the resistance would be lower.

Evaluation

There was sufficient data obtained to support the conclusion, as the
results all provide straight line graphs that are relevant to the
experiment. From the results tables and the voltage/current graphs it
can be concluded that the results are reliable. This is known because
there are no anomalous results, and because the results support the
hypothesis and scientific knowledge. When the resistances calculated
from these graphs were plotted on a new graph against the length of
wire, the results are all close to the line of best fit and are fairly
evenly spaced, which indicates that they are also reliable. The point
for the resistance calculated for the wire at 40cm long, however, was
slightly anomalous. This may be because of a human error in the
measurement of the results. It is possible that the wire could have
been at a slightly higher temperature, thus increasing the resistance
calculated, although, it was attempted to maintain a constant
temperature by leaving time for the wire to cool down in between each
measurement.

To obtain more reliable results, more sensitive equipment could be
used to measure the current and voltage of the wire. The experiment
could also take place in an environment with a controlled temperature,
to prevent fluctuations in room temperature from affecting the
results.

To improve the experiment, it could be repeated, possibly with
different voltages and different lengths of wire. This would produce
more results so that the experiment is more accurate. The experiment
could also be repeated with different types of wire to discover
whether the hypothesis, as the length of wire increases, the
resistance will also increase, is true for different types of wire.

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"Experiment to Discover How Factors Affect Resistance in Wire." 123HelpMe.com. 19 Apr 2014
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