Resistance- 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. Resistance is measured in ohms. During this experiment I aim to research and plan an experiment to investigate a factor that affects the resistance in a piece of wire. The possible factors I could change in this investigation are: 1 Length of the wire, 2 Thickness of the wire, 3 Type of metal- Copper, Nichrome and constantan 4 Shape of the wire, 5 Temperature of the wire,6 Density of the metal.

I have chosen to investigate the length of the wire because length is a continuous variable with a continuous range so I will be able to choose any lengths to investigate. I chose not to investigate thickness because although it is a continuous variable the wires available to me only come in set thickness that do not go up in regular intervals. I chose not to investigate type of metal because it is not a continuous variable so I would not be able to evaluate the investigation by linking two or more groups of data on a graph.

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I chose not to investigate the shape of the metal because it isn’t a continuous range. I could only use two options bent or straight. I chose not to investigate the temperature because although it is a continuous range it is very difficult to maintain a temperature, as you couldn’t use a water bath because of safety aspects. It is also difficult to measure the temperature of a piece of wire. I chose not to investigate the density of the metal because although it is a continuous variable I only have one set density available to me.

Prediction A longer piece of wire has a higher resistance because in a longer piece of wire there are more collisions between the electrons and the metal ions so there will be more successful collisions. In every successful collision energy is lost from the electron to the wire ions. The result is the voltage of the wire increases. The equation for resistance is resistance = voltage / current and as the current stays the same in the circuit and the voltage increases, the resistance increases. 10cm 20cm Preliminary Plan.

The aim of my preliminary work is to decide whether to use wire copper, constantan or Nichrome I will use and what thickness of either 32SWG, 38SWG or 26 SWG. I will need to use a wire with large resistance range that is a good conAmmeterVoltmeter ductor of electricity. The wire must not overheat easily. The apparatus I will need to perform the preliminary experiment will be:  Power pack (2volts)  Ammeter  Voltmeter Wires x 6 Crocodile clips x 2  Meter rule  Masking tape  Board marker Factors to control in preliminary experiment The independent variable will be:  The amount of resistance in different lengths of wire.

The variables that I will keep the same will be:  Material of wire-either Copper, Constantan or Nichrome.  Density of wire Temperature of wire Shape of wire- straight  Voltage- constant voltage of 2 volts. Circuit diagram for preliminary experiment Method 1 Set up the circuit as shown above with the power pack set at a constant voltage of 2 volts. 2 I will use 2 different lengths of wire in my preliminary, the largest 100cm and the smallest 10cm so I can find the material with the largest resistance range. Now 1 will make sure the power pack is off and insert the first wire at point x on the circuit diagram.

Now I will turn on the voltmeter and ammeter. 3 Next I will turn on power pack and record the first ammeter and voltmeter readings. The results may change due to heating so I must record the very first results shown. 4 Switch off the power pack and insert next wire. 5 Now repeat the experiment using the different wires and thicknesses and recording each result. Preliminary results These results show me the resistance ranges for copper, Nichrome and constantan. Material Length/ cm Voltage/Volts Current/Amperes Resistance/? Coppe Copper resistance range = 0. 3 ?

Preliminary Conclusion From my preliminary experiment I found that the material with the highest resistance range is Nichrome in a thickness of 32 SWG. Even though my results may not be very accurate because I did not take repeat readings and find an average, Nichrome 32 SWG had a much larger resistance range than the other materials and thicknesses. Nichrome had a resistance range of 15. 03 ? , Constantan had the second largest resistance range but was still only 7. 42 ?. Predicted results I have used resistivity to predict my resistance results in my final experiment.

The equation for resistance using resistivity is Resistance = resistivity x length / area of cross section of the wire The resistivity of Nichrome at 250C is 100 x 10-8 ohm-m. The radius of the wire is 0. 00014m2. To find the area of a cross section of the wire i use the equation for the area of circle Area of circle = ? r2 Area of circle = ? x 0. 000142 Area of circle = 6. 16m2 x10 -8 Working to find the resistance.

Ensure that the power pack does not exceed 2 volts in case the wires overheat.  I will also only leave the power pack on for short amounts of time so the wire does not overheat.  I will not perform the experiment in a wet area because water is a very good conductor of electricity and so this would be very dangerous.  I will not touch the wire once the power pack is switched on because the current will heat up the wire. Factors to control The independent variable will be: 1 The amount of resistance in different lengths of wire. The variables that I will keep the same will be:

2 Width of wire- I must keep the wire a thickness of 32SWG. If I change the width of the wire the resistance will change because there is more resistance in a thicker wire because there are more fixed ions so there are more collisions in the wire and more successful collisions means the resistance will increase 3 Material of wire- different materials will affect the amount of free electrons that are able to move through the wire. If there are more or larger atoms then there will be more collisions. This causes the voltage of the wire to increase causing a higher resistance.