To investigate how the length of a wire effects the resistance of it.

Resistance is a measure of how much energy needed to push a current through something. The electrons carrying the charge try to move through the wire however the because the wire is full of atoms which are constantly colliding and getting in the way, the electrons then have to use up more energy.

To ensure that the experiment is as safe as possible I will be taking the following precautions:

Handle the power supply carefully

Use a voltage that will not burn the wire

Be careful when touching the wire as it may be fairly hot

Start on a low voltage so the wire does not melt or burn instantly

Be careful when the wire is connected, as it will be hot

Be careful when cutting the wire

Ensure that the mains to the power supply are switched off when moving from the circuit when it needs to be measured.

The apparatus needed for the experiment are listed below:

Power supply

Voltmeter

Ammeter

Nichrome wire

Meter ruler

Crocodile clips

Connecting wires

To ensure a fair test and provide myself with accurate and reliable results I will be do the following:

• The power supply must stay on 4v

• The surrounding temperature constant

• Equipment should be kept the same

• Crocodile clips should be exactly on the edges of the measured length.
• salotape

I carried out a trial experiment to establish a suitable number to set the power supply on and to familiarise myself with the method as a whole so that if any problems arose I could correct when doing my original experiment. This would ensure that my results would be accurate in order for me to understand the relationship between the length of the wire and how it effects the resistance of it.

First I made sure that the equipment was set out as appropriate, shown in the diagram.

Then I plotted a rough sketch of my table with the appropriate headings.

The length of the wire will range from 10cm – 100cm whilst using intervals of 10cm.

Then I stretched the wire fully onto a meter ruler and taped it down. I changed the length of the wire by moving the crocodile clips across the meter ruler at intervals of 10cms. And put the current on the power supply on 2v before moving up to 4v in order to find a suitable current flow.

After carrying out my trial experiment I have decided to use a wire 1-meter long keeping the intervals 10cms apart. I found that this would in fact give me reliable results and would be easier to gain a proper understanding of what was happening, and make it easier to understand the relationship between the length and how it effects the resistance.

Therefor for my original experiment I will be keeping the length of the wire exactly the same.

As there were 2 people taking down the measurements this may have provided me with inaccurate results, therefore for the original experiment I will be making sure that the same person does the measuring at all times to ensure the results are as accurate as possible.

Also I found that you need a steady hand in order to get reliable results as an unsteady hand can give unreliable results. Therefore I will ensure that the person with the steadiest hand in the group takes the role of measuring the amount of current and voltage.

Also another thing I will make sure of is securing the wire tightly with selotape as the wire kept moving and had to be held down while taking the measurements. This way the wire will be kept in a steady position and possibly keep the wire straight.

I don’t think that there were any other dramatical changes that need to be made in the original experiment. And so the experiment will be carried out as such, correcting the mistakes in the process.

Below I have drawn a diagram to show how the circuit was set out:

 

Before starting the experiment I will make sure that the area I am going to work on is cleared, to avoid any accidents.

I will then bring together all the appropriate equipment needed such as the power supply, voltmeter, ammeter, connecting wires and crocodile clips and set up as shown in the diagram below. A table was drawn out to record the results.

I used a meter ruler, as the lengths I will be measuring are too big for a smaller ruler, and the meter ruler allows me to go up to 100cm.

Next I got the nichrome wire and selotaped it on to the meter ruler making it as tight as possible to ensure that it allowed me to get reliable results whereas in the trial experiment the wire was not tightly put into place.  I then moved the crocodile clips along the meter ruler, at intervals of 10cm. Making sure that the same person measured it at all times rather than two or three different people as in the trial experiment. At each interval plotting the results as appropriate. I repeated the experiment 4 times to ensure that the results were as accurate as possible. At the end I was fairly pleased.

I predicted that as the length of the wire is increased the resistance would also, in direct proportion to the length.

In any given metal wire, there are a number of atoms and free moving electrons. Resistance is caused by the free electrons moving through the wire and then colliding with the atom, making it more difficult for the electrons to pass through.

Therefore if there are a large number of atoms then there are going to be a large number of collisions between the electrons and atoms which in turn increases the resistance.

In a wire there will be a specific amount of atoms, and in a wire twice the length there will be double the amount of atoms. So this would lead to there being double the amount of collisions between the atoms and electrons which in turn increases the resistance by 2.

For example in a 10cm long wire there may be say 400 atoms blocking the electrons. Therefore in a wire of 20cm there would be 800 atoms, meaning that the resistance ha s in fact doubled.

And so this explains the relationship between the length and the resistance in which they are directly proportional.    

My prediction was proved correct as my graph shows that the line of best fit is a straight line indicating that when the length of the wire was increased then the resistance was also increase in proportion to each other.

My prediction was proved correct as I stated that as the length of the wire increased so did the amount of resistance. This was due to the number of electrons in the wire.

My graph which I obtained from the experiment proved my prediction correct as my results on my graph showed just that.

However I may have got inaccurate results because of the fact that it is difficult to be able to get an accurate length by eye, as the wire may not be the same thickness throughout and this could have affected my results.

My results were reasonably accurate and I feel that it would be difficult to try and improve on it, as there were no anomalous results.

However if I were to do the experiment again I would use newer more accurate voltmeters and ammeters. I would also have a, more accurate method of measuring and taken more readings to ensure even more accurate results and allow me to get a more average result.

I feel that the experiment was not poorly carried out and I was fairly pleased with the outcome of my results as it proved my prediction correct, that the length of a wire does in fact effect the resistance of  it and that when length is increased then resistance is also.