Factors Affecting the Resistance of a Wire


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Factors Affecting the Resistance of a Wire

The aim of this experiment is to investigate one factor that affect
the resistance of a wire. I will do this by performing an experiment.
First I will need to identify the factors that effect resistance.
There are a few factors that affect the resistance, it is determined
by the properties an object has. This is know as resistivity.

The factors I can investigate are :

Ÿ Temperature

Ÿ Length

Ÿ Cross-sectional area/width

Ÿ Material (resistivity)

The factor I shall investigate is the length of a wire.

Background Knowledge

Resistance is when electrons travelling through the wire are impeded
by the atoms within the wire. Since the electrons are charge carriers
when they collide with the atoms in the wire less pass through. There
fore less current passes through with the same voltage. Simply it is
how hard it is for the electrons to pass through the wire.

Temperature:

When the metal wire is heated , more energy s given to the atoms,
therefore they vibrate more. From this there is a greater chance of
collisions with the electrons and they are impeded more, therefore
less charge is passed by the electrons and the resulting current is
reduced.

This means while conducting the experiment the temperature of the wire
must be kept constant to maintain a safe and fair test.

Cross-sectional area/ width:

If the cross sectional area is increased there is more space for the
electrons to move freely making less collisions so more current will
pass through making the resistance decreased. I have done a diagram
below.

[IMAGE] [IMAGE]

Small wire Large wire

Length:

If the length of a wire is increased there are more atoms for the
electrons to collide with. There for less gets through meaning the
current is less so the resistance is increased. I have done a diagram
below to help me understand this.

Material/resistivity :

Different wires composed of different metals will have differing

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properties. This includes resistivity, (Resistivity = (R A)/l, Where R
is the resistance of the conductor, A is the cross-section in square
metres, l is the length of the conductor.)

This means that some materials will have varying resistances for the
same voltage and current than others. This also means that I will have
to use the same material all the way through my experiment.

Ohms law (W)

This is how I will be calculating the resistance. This is a definition
of Ohms law (found from the internet)

"Ohm's law states that the amount of current flowing in a circuit made
up of pure resistances is directly proportional to the electromotive
force impressed on the circuit and inversely proportional to the total
resistance of the circuit."

This means that a circuit with 100% resistance the voltage and
resistance will be the same and there will be no resulting current.
This is summarised in the equation

R(W)=V(volts)/I(amps)

This equation will be used in the experiment to calculate the
resistances along the varied length of wire by measuring the values of
V and I.

[IMAGE]

Hypothesis:

From the background knowledge above I can conclude that I expect the
resistance to increase as the length of the wire increases. I think
this because there are more collisions between the electrons and atoms
in a longer wire there fore since the electrons carry the charge
therefore less current will get through.

Preliminary tests:

Before I start with my final experiment I need to do a test experiment
or preliminary test. I need to do this so that I can test the safety
of my experiment, the accuracy of the experiment and to confirm what
variables to use.

In my preliminary tests I decided to use the following equipment and
units.

Ÿ Power pack

Ÿ Wire board (with 5 lengths of wire 1,2,3,4,5 meters)

Ÿ Ammeter (amps, to measure the current, I)

Ÿ Voltmeter ( Volts, to measure the voltage, V)

Ÿ Connecting wires

The units I shall be using are the following.

Ÿ 8 volts

Ÿ 15 different lengths of wire (1 to 5 meters)

Method:

From doing the preliminary work it helped me to see what was the most
efficient way of doing the experiment:

1. Set up the circuit like the diagram below.

2. Connect the connecting wires to the 1m wire

3. Measure the voltmeter and ammeter

4. Record the results from the ammeter n voltmeter

5. Redo steps 3&4 for 2,3,4&5 meter wires

6. To ensure accuracy make sure I redid the tests three times.

7. Take an average of the 3 tests to ensure accuracy

8. Put the results in to a table

9. Plot the results in a graph that you can read off

Diagram and apparatus:

Ÿ Power pack

Ÿ Wire board (with 5 lengths of wire 1,2,3,4,5 meters)

Ÿ Ammeter (amps, to measure the current, I)

Ÿ Voltmeter ( Volts, to measure the voltage, V)

Ÿ Connecting wires

Safety:

It is important that when doing any experiment to take precautions.
These are the following steps I took to ensure that I was safe and
others around me were too. I had to make sure I turned off the power
pack when not in use because it could heat the wire and it could burn
some one. I also had to be careful of the wires they could potential
cut some one. Also the use of Goggles might be needed.

Fair test:

I need to make sure that it is a fair test so that the results are
accurate. In doing this I need to make sure certain things are kept
the same. These are the things I am going to keep the same

Ÿ Material of the wire

Ÿ The temperature of the wire (room temperature)

Ÿ The same thickness of the wire

Results:

Length (meters)

Volt (v)

Current (I)

Resistance (W)

1 m

2 m

3 m

4 m

5 m

1m

2m

3m

4m

5m

1m

2m

3m

4m

5m

This is the table for the results I obtained. Below is a table of
averages, I did these averages so that it would help me be more
accurate and make my graph easier to read and more accurate. As I said
before I did the calculated resistance for each meter of wire I did
this by using Ohms law and the following equation.

Resistance= Voltage

Current

Length (meters)

Volt (v)

Current (I)

Resistance (W)

1m

2m

3m

4m

5m

I can now put these results in to a graph. The graph should show that
my hypothesis is correct and that the resistance will increase as the
length of the wire increases.

Analysis of Results:

From the graph and table of results i can see a pattern emerging. I
can see that the results match my hypothesis, although there is an
anomalous result and


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