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# Factors Which Affect the Resistance of a Wire

Extracts from this document...

Introduction

## By Richard Roaf

Introduction:

Resistance is a force that 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. e.g. The filament across an electric bulb is quite thin as needs to resist the flow of particles for the bulb to glow.
Resistance is measured in ohms.

George Ohm discovered that the emf of a circuit is directly proportional to the current flowing through the circuit. This means that if you triple one, you triple the other. He also discovered that a circuit sometimes resists the flow of electricity. He called this resistance. He then came up with a rule for working out the resistance of a circuit:

V/I = R

V - Volts
I - Current
R - Resistance.

Apparatus:

Power Supply
Ammeter
Voltmeter

Resistance Wire
Meter Ruler
Crocodile Clips
Connecting Wires

I set up my experiment as shown above.

Extra Background Information :

The total resistance of resistors in series is the sum of the resistance of each one. Each cm of wire has a particular resistance, if you double the length of wire, it is like having two of the shorter wires in series.

Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire.
These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire.

Before starting my coursework I have decided to chose a factor that will affect the resistance of a wire.

Middle

Wire

(swg 36)

Area

Mm2

Length

Voltage

(Volts)

Current

(Amps)

Resistance

(Ohms)

Nichrome

0.117

4x50cm

4.26

0.82

5.2

We see from this second preliminary test that the resistance has gone down steadily with 4x Nichrome wire. This is because the resistance of the test with 4 wires is roughly a fourth of the resistance when measured with one Nichrome wire.

Safety Precautions:

There are not many safety precautions that need to be taken into consideration, in this experiment. The main three I can think of are stated below:

1. We did not carry out the experiment in wet areas, as water is a very good conductor, and thus could be very dangerous.
2. We did not touch the wire when the battery is switched on, because the current would heat up the wire and so could burn us.
3. We also used a safety mat so the hot wires did not damage the table in any way.

Aim: To investigate how the area affects the resistance of a wire.

Prediction:

I predict that if the area increases then the resistance will decrease in proportion to the area. E.g. If with 1 length of wire the resistance is 10 then with 2 lengths of wire the resistance will be 5 I think this because as I know from my scientific knowledge that:

Electric current is the movement of electrons through a conductor. In this experiment a metal wire (Nichrome will be the conductor). So when resistance is high, conductivity is low. Metals such as Nichrome conduct electricity well because the atoms in them do not hold on to their electrons very well. Free electrons are created, which carry a negative charge, to jump along the lines of atoms in a wire, which are in a lattice structure. Resistance is when these electrons which flow towards the positive collide with other atoms, they transfer some of their kinetic energy. This transfer on collision is what causes resistance. So, if we double the area of wire, the
space that the electric current has to pass through is larger so it has more space to go through. This decreases the number of collisions and energy transferred by half, so half the amount of energy is required. This means the resistance is halved.

This would also happen if you increased the number of wires by more than one and so if you increased the area of wire by more than one, so if you increased the number of wires to 3 then there would be one third as many collisions and so the resistance would be a third of what it would be if you only used one wire and with four then it would be a fourth. So we can work out a formula for this:

Resistance for one wire (Ohms) = R

Number of wires = N

New resistance (Ohms) = X

X   =      __R  _

N

An example of this is if the resistance for 1 wire if 50 Ohms and if you increase the number of wires to 5 then you can work out the new resistance:

X   =      __50      = 10

5

So from this we can see that the new resistance is 10 Ohms

My predicted graph is on the following page. It shows what I think the graph of results should be based on my prediction.

My predicted graph shows that the resistance should decrease as the area of wire increases. This means they will be inversely proportional to each other .The graph is based on my scientific knowledge and Ohms law (Ohms law is stated in my conclusion.

Results:

We conducted 2 tests and then we found an average resistance from these results. We set up the experiment as shown on the first page. We started with one length of 100cm Nichrome 36 and then added one each time until we had 6 wires attached to provide resistance.

The 2 tables of results are below followed by the table with the average resistance.

First test

 Wire (swg 36) AreaMm2 Length (cm) Voltage(Volts) Current(Amps) Resistance(Ohms) Nichrome 0.0293 100x1 4.55 0.12 37.9 Nichrome 0.0586 100x2 4.59 0.23 20.0 Nichrome 0.0879 100x3 4.11 0.36 11.41 Nichrome 0.1172 100x4 4.16 0.45 9.24 Nichrome 0.1465 100x5 3.48 0.48 7.25 Nichrome 0.1758 100x6 4.26 0.68 6.5

Conclusion

I don’t think I could really improve on the way the experiment was done because my results were very accurate, as I had no anomalous results.
I also found that the experiment was quite easy to set up, as it was simple and uncomplicated.

Further experiments I could do related to the resistance in a wire, would be to see whether the following factors would make a difference in the resistance of a wire: (I have made a prediction for each factor from my own scientific knowledge on how I think the resistance would change in a wire for that particular factor )

1. Wire width:

I think that if the wire width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.

2. Temperature:

I think that 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.

3. Material:

I think that the type of material of the wire will affect the amount of free electrons, which are able to flow through that wire. This is because 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 numbers 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.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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