Resistance in a Wire.

Abdulrehman JAVAD.

George Mitchell School (13410)

Science Coursework.

Resistance in a Wire

Aim

The aim of this experiment is to find out if or how different lengths affect the resistance of a wire by carrying out an investigation.

Scientific Information

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.

Resistance is measured in ohms. A resistor has the resistance of one ohm if a voltage of one volt is required to push a current of one amp through it. Resistance is dependent on several factors, heat, cross sectional area, substance and length. Length is the variable that I have chosen to investigate. The resistance of a wire increases as the length increases.

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 resisted 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

Ohms law states that ‘the current flowing through a metal wire is proportional to the potential difference across it (providing that the temperature remains constant’. A thin wire would resist more than a thicker wire. This because it is more difficult for the same amount of electricity to ‘cram’ into a smaller space and more energy is needed to push it through, and in this case the energy is volts. As the length of wire increases the resistance increases.

In this investigation I am going to look at the resistance of a wire when a current is running through it and see what affects the resistance of the wire. These are the four main contributors to the amount of resistance put up by a wire:

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Length of wire

The longer the wire is the more particles there are. This means that there are more obstacles for the electrons to collide with. The more particles bumped into means that it would have a higher resistance.

Diameter of wire

This is much the same as the length of wire in that there are more particles for the electrons to collide with and so this makes the resistance of the metal a high one.

Material of wire

Different elements have different sizes and different amounts of atoms. The more atoms there are ...

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Length of wire

Diameter of wire

This is much the same as the length of wire in that there are more particles for the electrons to collide with and so this makes the resistance of the metal a high one.

Material of wire

Different elements have different sizes and different amounts of atoms. The more atoms there are or the larger the atoms the more the electrons hit them and therefore the resistance goes up.

Temperature of wire

When the temperature goes up the electrons and atoms in the metal receive more energy therefore they bounce around more and have many more collisions with one another. This would then impede the electron’s passage and the resistance would go up.

I am going to work with length in my experiment.

Prediction

I predict that the resistance level will rise as the length of the wire increases. This is because resistance is caused by electrons bumping into atoms. If the length of the wire is increased, there are going to be more atoms, so it is more likely that the electrons are going to collide with the atoms. So if the length doubles, the resistance should also double. This is because if the length is doubled, the number of atoms will double, resulting in twice the number of collisions, slowing the electrons down, and increasing the resistance.

Plan of Experiment

For my experiment is with a meter ruler with a wire stuck to it, so it can be measured. I will connect it to a power supply of 2v then have a voltmeter connected in parallel and an ammeter connected in series to the wire. I will then change the length of the wire to find out the lowest and highest results for current and potential difference.

Diagram

Equipment

The equipments I will be using for the experiment are:

Power supply
1 Ammeter
1 Voltmeter
1 Metre ruler
2 crocodile clips
Copper wire of up to 500 mm in length.

Method

I have chosen to use Copper wire because from my own knowledge I know that this type of material and thickness will have the most resistance and therefore it will be easier to measure and differences in resistance. To ensure a fair test whilst carrying out my 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 2 volts and the same width and same material, which is Copper.

Meter ruler: To measure the wire being tested.
Copper wires: Same width of wire and same material but testing different lengths.
Crocodile clips: To connect the wire to the rest of the circuit.
Voltmeter & Ammeter: To measure the resistance.
Wires: connect the above items and to make a circuit.

In my experiment I have chosen to use an ammeter and voltmeter, I have done this so that I can work out the resistances from the volts and amps. I shall calculate the resistance of the wire using the equation below.

RESISTANCE = VOLTS / AMPS

To do the experiment:

I set apparatus as shown above in the diagram.
I kept the voltage at 2V. (So that there is not too high current passing through the circuit.)
To begin with, I measured copper wire by meter ruler so that it is set to 100mm and then positioned it between the two crocodile clips to complete the circuit.
I turned on the power supply and recorded what the ammeter and voltmeter read.
Then I set the wire from 100mm to 200mm by the help of meter ruler remembering to keep the voltage the same. Turned on the power pack and recorded what the ammeter reads.
I keep measuring and setting the wire to 500mm.
Then I recorded my results in table.
I repeated experiment 3 times to increase reliability.

Safety

Whilst doing experiment, must take safety into consideration. Before using the power pack, the pointer should be at 0 volts. It is important to be careful while using the power supply. While handling live wires, it is essential to be careful. The voltage should be kept low for safety, and for when the wires heat up. Also the circuit should be complete before turning on the power supply.

Results

Averages:

Graph

Below is a graph to show my table results.

Conclusion

In my prediction I said that if the length increases than the resistance would also increase in proportion to the length. From my graph I have shown that my prediction was correct, as the Line of Best Fit is a straight line and have positive coloration proving that the resistance of the wire is proportional to the length of the wire.

The length of the wire affects the resistance of the wire because the number of atoms in the wire increases or decreases as the length of the wire increases or decreases in proportion. The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase. If the wire is half the length of the wire and so has half the number of atoms, this means that the electrons will collide with the atoms half the amount of times. Also if the length of the wire was trebled or quadrupled then the resistance would also treble or quadruple.

I can now write the following equation by looking back at my investigation:

Length Resistance
Length is proportional to resistance

Evaluation

Overall I think my experiment was quite successful. It was quite an easy experiment to perform so I feel that I have obtained quite good quality results. I might have made my results a bit larger or a bit smaller because when averaging current and calculating resistance, I calculated the results to nearest whole number which could change the result.

I don’t think there were really any anomalous results as on my graph; the line is straight with it running through most of the points. I have compared my results with another member of my class, who done the same experiment and I also looked upon the results of same experiment on the internet, the results were very similar to mine showing that they are reliable. My results are also reliable because my results table does not show any individual anomalous results this means that I did not have to leave any results out of my averages because they were anomalous. Also on the graph I can see that none of the averages plotted are anomalous because all the averages lie along the same straight line. If I was to carry out the investigation again I can think of some improvements that I could make to get better results, I would have to make sure the wire was the exact right length and also it was not bent because it could make the readings different. Also it would be purposeful to give time to wire to cool down after taking each reading.

If I had more Time I would of liked to of tried more lengths and material of wire or try out some of the other variables (voltage, current etc.).