Resistance in a wire.

Introduction

I have been asked to investigate what factors could affect the amount of resistance in a wire. For this investigation, I believe that altering the length of the wire throughout the experiment will be the best method.

Investigation into how the Length of Wire in a Circuit affects the Resistance

Planning Section

Science Theory

The information in the Science Theory section and the Prediction was taken from Nuffield Co-ordinated sciences and The Usbourne Illustrated Dictionary of Science. The various factors that could affect the resistance in a wire are as follows.

The thickness of the wire - if a wire has a diameter of 4mm then there will be more space for the electrons to move in and electricity can be passed quicker that in a wire with diameter of 2mm.

The material the wire is made of - if the wire in question was made from gold, which is an excellent conductor for electricity as it has a large number of electrons that move freely, so the electricity passes from one atom to the next.

Voltage - Voltage may also be linked to the amount of resistance in a wire as the more electricity there is trying to get through the wire the harder it will be as there will be less space for it to fit through, so therefore there will be more resistance.

The length of the wire - for example if you obtained a small stretch of wire say 3 cm long then there will be less resistance than a wire that is 30 cm long. The reason behind this is that if the electricity only has to travel a short distance then there are potentially fewer atoms that could slow down the electricity flowing through the wire, however if it is a longer piece of wire made of the same material then there should be 10 times more resistance than in the 3cm length wire.

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Prediction

Due to Ohms law stating 'The current in an object at constant temperature is proportional to the potential difference across its ends. The ratio of the potential difference to the current is the resistance of the object.' then I believe the shorter the piece of wire then the lower the resistance will be. The reason I believe this is because there will potentially be more atoms in a longer piece of wire for the electricity to crash into, as stated in Science Theory section, so the electrons will be able to move less freely and will be ...

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Prediction

The diagrams that I have produced below will help to back up my theory, the red line shows the path of the electricity and how much resistance it encounters.

Diagram A is the stretch of short wire, this shows us that the electricity finds it easier to pass from one particle to another.

Diagram B in Diagram B, there are potentially more electrons for it to hit and there is of course further distance to travel.

Diagram A

Diagram B

Here is a table of preliminary results that I collected before the actual practical work began, there is also, on the page after my preliminary results, a graph that I have constructed to show what I think it will look like when I take my main results and also to back up my theory that it is directly proportional, these will not be included in the final results table or plotted on my final graph. The readings that I collected will probably be slightly different to my final results, as it is only a trial run. The table also goes to 5 cm, I was initially going to stop at 5 cm however the wire burned out before we could note the results, so any following tables will only go to 10 cm.

Preliminary Results Table

Apparatus

There will be many different pieces of apparatus that will be used in my experiment, these are listed below:

A piece of wire 100 cm long.
Pieces of wire that will connect up the voltmeter, the ammeter, the power supply and the 100 cm piece of wire.
An ammeter, this will be used to discover the amount of current that is flowing through the wire.
A voltmeter that will record the amount of volts that are being used and to calculate how much resistance there is in the wire.
A power supply.
A meter board, this will be used to keep the wire perfectly still so that results can be taken quickly and easily, it will also ensure that I reduce the wire by the exact amount each time.
Crocodile clips

Below is a diagram of the circuit that I will be using for my investigation, the red line is the wire in which I am investigating the resistance.

Voltmeter

Ammeter

This is a power supply

This is a length of wire that connects the circuit.

Method

To complete the experiment I have done, follow these easy steps:

Stretch the wire to be investigated across the metre board and secure in place at both ends.
Connect two pieces of wire to the voltmeter, on each end of the wire that is not in the voltmeter, place a crocodile clip.
Attach one crocodile clip to the wire you are investigating at 0 cm, the other is attached at 100 cm.
Attach one connecting wire to the end of the metre board at 0 cm and connect to the ammeter.
Fit another connecting wire into the ammeter leading to the power supply.
To complete the circuit, take the remaining wire and connect from the power supply to the metre board at 100 cm.

The circuit should look like the one shown in the Apparatus section.

Note: The ammeter must be in series and the voltmeter in parallel

Plug power supply into the mains and switch on.
Set the power supply to 4 volts.
Ensure that the voltmeter and ammeter are working, if not check that the circuit is complete.
Take two readings – one from the ammeter and one from the voltmeter, note down the results.
Remove the crocodile clip at 100 cm and slide down to 95 cm – repeat process as at 10.
Continue process with intervals of 5 cm until you reach 10 cm.
Work out the resistance for this set of results using the equation R = I/V.
Repeat the process of obtaining results twice more also calculate the resistance.
You can now calculate the average results for the volts, current and resistance.

I will be keeping everything like the width of the wire and the material that the wire is made of constant throughout the experiment, the amount of voltage from the power supply will also remain the same as will the connecting wires to ensure that it is a fair test and will not affect the resistance.

To make sure that the results I take are accurate, I will tape down the wire on to the board and place the crocodile clips directly on the measurement that I am taking.

Throughout the experiment, I must ensure that everything is being done safely, this is not a very dangerous experiment but I must keep the power supply and the wires well away from water and keep the power low.

Despite this I will be unable to control human error, to try and guard against this I am taking three sets of results and will be taking 19 in each set, this limits what can go wrong, there will also be an average table created from my three sets of results.