To investigate how the resistance of a wire is affected by changing the length of a wire.

Physics coursework.

Aim:-

Resistance is the force, which stops the flow of an electrical current around a circuit so that energy is required to push the charged particles around a circuit.

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.

Resistance is affected by a number of things, these are:

Temperature: because if the wire is heated up the atoms in the wire will start to vibrate more because of the 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 means that there will be an increase in resistance.

Material or type: Firstly the material you use must be a conductor or no electricity will flow at all. W will be using a metal wire to measure what affects its resistance. But there are different types of wire. The type of wire can affect its resistance because if the atoms in one type of wire are more closely packed together. Then the electrons will have more frequent collisions and the resistance will increase in that wire. The type of wire also affects the amount of free electrons that are able to flow through the wire. If there are more atoms there will be more electrons available meaning less energy per e-.

Wire length: if the length of a wire increases then the resistance will also increase. As the electrons have a longer distance to travel and so more collisions occur. The more collisions that occur the greater the resistance.

Wire width: if the wires width is increased then the distance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increase in space between the atoms there should be fewer collisions. Less collisions means less resistance.

All of these things that affect the wires resistance must be kept constant in order to obtain accurate results. The only thing that we will change will be our chosen variable. For this investigation I have chosen to have wire length as my variable. So that I can investigate the relationship ...

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Resistance is measured in Ohms. We can calculate resistance in a wire using Ohms law:

Resistance = Voltage (V) or R= V

Current (A) I

You cannot measure resistance directly. So I will have to use this equation in order to calculate the resistance. From the readings that I take.

We will take a reading of the voltage and current from every piece of wire measured. Using an Ammeter to measure the current and a voltmeter to measure the volts. We will set up our experiment like the circuit I have designed below.

Key:

= Cell = Ammeter = Voltmeter = Wire

To make our experiment a fair test, we will need to keep all the factors that affect the resistance of a wire constant. To prevent it from affecting the experiments accuracy. The only thing that will be changed is the length of the wire. I chose this as my variable because after researching into the factors that affect resistance. I thought that this would be the easiest to make sure it was accurate and would draw the most conclusive results. I decided that to be able to draw a clear conclusion from my results I would need to do a maximum of 10 experiments and a minimum of 6. We were given a length of wire a meter long, as the longest length of wire we could use.

We then divided it up so that we would be taking 10 readings at:

10cm, 20cm, 30cm, 40cm, 50cm, 60m, 70cm, 80cm, 90cm, 100cm.

I then needed to decide what voltage would give us the most accurate results and which type of wire to use. So I decided to carry out preliminary experiments in order to make the decision. The preliminary experiments would also help me to familiarise myself further with the method, and if I came across any problems I could correct them. I would them be able to obtain precise and reliable results in my main experiment without any of these difficulties.

Preliminary results:

Experiment 1: Wire length: 100cm.

Wire type: constantan.

Volts: 12

Observations: this experiment proved inconclusive. The voltage was far too high. So I decided to experiment with the lower voltages.

Experiment 2: Wire length: 20cm

Wire type: copper

Volts: 0

Observations: there was no voltage so the experiment failed. Showing that we need a higher voltage than this.

Experiment 3: Wire length: 20 cm

Wire type: copper

Volts: 2

Observations: the voltage was still too low to get a current. But the volts = 0.36.

Experiment 4: Wire length: 20cm

Wire type: copper

Volts: 4

Observations: A=0.03 V=1.63

Experiment 5: Wire length: 20cm

Wire type: copper

Volts: 6

Observations: A=0.04 V=2.86, the wire burnt when carrying out this experiment so we decided not to increase the voltage further.

From our preliminary results I decided that for my main experiment I would use copper wire, set the power pack voltage to 4 Vols, carry out the experiment at room temperature and keep the wire width the same throughout. This way I can insure my experiment will be a fair test and have the most accurate results possible. I have also decided to repeat the experiment twice for every length of wire. In order to check all my results are accurate.

My preliminary results also helped me to see if my circuit design was working correctly, which it did. So I will be able to use it for my main experiment also.

When I have carried out my experiment I will collect my results into a table, take the averages and then use ohms law to calculate the resistance.

I will then plot the results onto a graph. Showing the length of a wire against the resistance. So that I will be able to draw a clear and accurate conclusion.

I predict that as I increase the length of wire the resistance will also increase. I predict this because I know that if you increase the distance the electrons must travel. You in turn increase the chance of more collisions occurring. Meaning that there will be a greater resistance.

I also predict that the increase in resistance will be directly proportional to the increase in wire length. I predict this because I think that if you double the wire length you will double the resistance. If the length of wire increase and the resistance increase are directly proportional. I predict my graph will look like the one below.

Resistance

Wire length

Results