Investigating how the Length of a wire Affects the Resistance.

Investigating how the Length of a wire Affects the Resistance

Planning –

There are four factors that affect the resistance of a wire.

They are: Area, Length, Material and Temperature

I am investigating length. I am doing this because length is the most practical one to do and I won’t have to change the wire. There is no point doing area because I would have to change the wire and keep the length the same. The same goes for material and temperature. I am hoping to achieve how resistance affects a piece of wire when the length is changed.

This is a diagram of a circuit:

Here is a diagram of the experiment I am going to set up:

Fair Test –

In this experiment the variables must be controlled. This means I must keep the same type of wire, same material of wire, same cross sectional area and a constant temperature (room temperature).

These factors must be controlled to maintain a fair test. I must also ensure that when I change the length it is on the exact length on the ruler.

Safety –

I will ensure that none of the wires are frayed and that there is no water near any electric equipment; as in all electrical experiments.

Scientific Theory –

Electric current is the movement of electrons through a conductor. In this experiment a metal wire will be the conductor. When resistance is high, conductivity is low. Metals conduct electricity well because atoms in them do not hold onto their electrons very well.

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Scientific Theory –

Free electrons are created, which carry a negative charge which jump along the lines of atoms in a wire which are in a certain structure. Resistance is when these electrons that flow towards the positive collide with other atoms, they then transfer some of their kinetic energy. This transfer on collision is what causes resistance. So, if I double the length of a wire, the number of atoms in the wire doubles. This increases the number of collisions and energy transferred twice, so twice the amount of energy is required. This means that the resistance is doubled.

Prediction –

I predict that the longer the piece of wire, the greater the resistance will be, and in a shorter piece of wire there will be much less resistance. This is due to that fact of free moving electrons being resisted by the atoms in the wire. In a longer piece of wire, there would be more atoms for the electrons to collide with so the resistance will be greater.

The relationship with the length of the wire and resistance should be proportional. This is because in a wire twice the length of another there would be double the amount of atoms causing resistance.

An example of this would be in a 40 cm wire. The electrons would have to travel double the distance if it had to go through a 20 cm wire.

Preliminary Experiment –

The reason for doing a preliminary experiment is to practice for the real experiment and to make any changes in the real experiment if needed. I set the experiment up in exactly the same way, using 2 volts on the power supply. In this preliminary experiment I only recorded the following lengths:

100 cm
70 cm
50 cm
20 cm

I only did one reading for each length in this preliminary experiment as you can see below in the results table.

These results seemed reasonable so therefore I won’t change any methods for when I do the real experiment.

Apparatus –

Power supply
Wire
Metre rule
Tape
Leads
Crocodile Clips
Voltmeter
Ammeter

Method –

A simple circuit will be set up (like the one above) to read the voltage and current when the length of the wire changes. The power supply will be set on 2 volts. The length will range from 10 cm to 100 cm (1 metre) with changes of 10 cm each time.

A length of wire is attached to a metre rule. It is the attached to the circuit (shown above) with crocodile clips.

One of the crocodile clips is then moved around the metre rule from 100cm to 90, 80, 70, 60 etc…

I will take 3 readings from the voltmeter and ammeter at each length. In these three recordings I will adjust the resistor to various lengths; this will give me a good average. This will also give a range of readings to determine resistance using the formula R=V/I

The readings will be noted in three different categories:

3 readings from the voltmeter
3 readings from the ammeter
the resistance (R=V/I)

Then I will gather my results and plot a graph showing the average resistance at each length.

Analysis –

The graph was almost a straight line but however at 90 cm the resistance was lower, I repeated the experiment for 90 cm and got the same results. This could have occurred due to a bend in the wire. However after repeating the experiment various times there seems to be no reasonable explanation for this. However, all the other points were in a straight line through the origin. This means that if the length is 20 cm and the resistance is 1 Ohm then at 40 cm it should be 2 Ohm’s.

My results are at 20 cm 0.89 Ohm’s and at 40 cm the resistance is 1.80Ohm’s which is almost double the size.

The results that I have obtained support my prediction. This is because in the prediction I said that as the wire length increased, the resistance should increase. I also said that the link should be proportional.

These results have shown that it is true.

The line of best fit clearly shows that the results followed the expected pattern very well. The points are very close, if not touching the line.

This shows how the results were directly proportional through out, as the gradient remained the same.

Evaluation –

The results of this experiment would be very difficult to improve on because they are reasonably accurate, and there were no drastically anomalous results.

If I were to do this experiment again I would take a much wider range of readings and more readings so that an accurate average could be taken.

I would also consider making the wire much longer and taking shorter distances. For example 10 cm, 15 cm, 20 cm, 25 cm, and so on.