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Investigation the Factors That Affect Resistance of a Conductor

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Investigation the Factors That Affect Resistance of a Conductor

Physics Coursework

The purpose of this experiment is to find out what effects the
resistance over a length of wire. I have identified four factors,
which could effect the resistance. They are:

Length of the wire- The longer the wire is the longer the electrons
have to travel and creating a higher chance of collisions with other
electrons

Material used- The more dense the conductor (the closer the electrons
are) the harder it is for other electrons to pass through the
conductor and so more collisions between particles, creating a higher
resistance.

Temperature- If the temperature of the wire is high then the atoms in
the wire will start to vibrate and so increasing the amount of
collision between particles therefore increasing the resistance

Cross-sectional area- If the wires width is increased the resistance
will decrease. This is because the electrons have more room to move
and so the chance of a collision with another electron is less.

In this experiment the length of the wire will be investigated to find
how that factor effects resistance. I have chosen this factor, as this
will be the simplest to collect the results from the experiment. The
length of the wire is an simple factor to measure unlike the
cross-sectional area of the wire as that measurement may vary across
the wire. Controlling the temperature of the wire is also unpractical
with the equipment available in school.

I predict that when the length of the wire is increased the resistance
over the wire will also increase and when the length of the wire is
decreased the resistance will also decrease. I have also predicted
that when the wire that is tested is too small the wire will glow
and/or melt and break the wire.

Equipment I will need:

Power Supply- output of 2V
Ammeter
Voltmeter
100cm of Nichrome wire (an alloy of Nickel of chrome)
Meter Ruler
Two Crocodile Clips

The factors, which must stay constant in this experiment to make it
fair, are the output voltage from the power supply, which should
remain the same throughout measuring. When there is not load on the
power supply the voltage will rise until the power is being used when
connected to the circuit. The surrounding temperature should not rise
or lower too much but that is mostly out of our control. The only
factor that should change in this experiment is the length of the
wire, but this can only be measured as accurately as about half a
millimetre by using the meter ruler.



Method
======

First I will measure out just over 100cm of Nichrome wire and tape the
ends of the Nichrome wire to the ends of a meter ruler and make sure
that it is tight across the length of the ruler. I will then connect
the Voltmeter across the length of the wire in parallel and the amp
meter in series in the circuit as shown in my diagram. These two
instruments are used to work out the resistance across the wire when
the results are being taken. To work out the resistance we would use
the equation:

Resistance (ohm) = Potential Difference (volts) รท Current (ampere)

After the equipment is set up you would start the experiment. Due to
safety we are not to use any length below 30cms as the wire melts/
burns. This is because when the voltage is put through any length of
wire the same amount of heat is let out of the wire. Whether it is 5cm
or 1000cm, but when the wire is smaller the heat is given out over a
small space and is concentrated unlike it being spread over a large
distance. This then gives out a lot of heat in a small space and that
heat is enough to melt the wire and break the connection.



[IMAGE]
=======

Power Supply 2v

Diagram

[IMAGE]

Figure 1.1

[IMAGE]





This is a diagram of the experiment that I used in this experiment.
There are three different measurements that you must record. One is
the length of the conductor being tested (Cm) the reading on the amp
meter, connected in series,(A) and the reading from the volt meter,
connected in parallel, (V). By using these three measurements you can
work out the resistance through the Nichrome wire and how it relates
to the length of the wire.

To make the experiment fair the nichrome wire was made as tight as
possible to avoid slightly shorter or longer lengths, ie to reduce the
opportunity for error in our results. Also changes of temperature in
the room that can be help by turning on a heater or opening the door
were avoided in order to get accurate results.



Results
=======

Experiment 1 Results

Length (Cm)

Current (A)

Voltage (V)

Resistance (Ohms)

30

0.31

1.64

5.29

35

0.27

1.66

6.15

40

0.25

1.67

6.68

45

0.22

1.68

7.64

50

0.21

1.69

8.05

55

0.19

1.69

8.89

60

0.18

1.7

9.44

65

0.16

1.71

10.69

70

0.15

1.71

11.40

75

0.14

1.72

12.29

80

0.14

1.72

12.29

85

0.13

1.72

13.23

90

0.12

1.73

14.42

95

0.12

1.74

14.50

100

0.11

1.74

15.82

Experiment 2 Results

Length (Cm)

Current (A)

Voltage (V)

Resistance (Ohms)

30

0.31

1.66

5.35

35

0.28

1.67

5.96

40

0.25

1.68

6.72

45

0.23

1.69

7.35

50

0.21

1.7

8.10

55

0.19

1.7

8.95

60

0.18

1.71

9.50

65

0.16

1.71

10.69

70

0.15

1.72

11.47

75

0.15

1.72

11.47

80

0.14

1.73

12.36

85

0.13

1.73

13.31

90

0.12

1.74

14.50

95

0.12

1.74

14.50

100

0.11

1.75

15.91



[IMAGE]




Figure 1.2




The graph shows good correlation and I cant find any results that
stick out as being an error (outlier). By including a line of best fit
onto my graph I cant predict results that weren't recorded in the
original experiment. With this red line I can predict a rough estimate
of the resistance through a wire measuring 20cm, I would predict that
it would have a resistance of about 4 ohms.

In figure 1.2 it shows that when the length of the wire was increased
so did the resistance over the wire which is what I predicted. The
reason why the resistance increases over distance is because the free
flowing electrons in the wire have a higher chance of colliding with
each other if they are travelling over longer distances. When the free
flowing electrons collide, some of the energy they carry is lost in
heat. This loss in energy is what heats the wire and sometimes, enough
will melt the wire. When the electrons hit each other they loose
energy in heat.

Preliminary work was conducted to see what lengths of wire should be
used. We found that using a wire that was too long was impractical and
so a shorter wire, up to 1meter was to be used. We found that using a
length less than 30cm made the wire quite hot and so we did not test
any wire less than 30cm.

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