An investigation to see whether the chosen factor affects the resistance of a piece of wire.

Aim: To study the factors which affect the resistance of a wire.

Background Knowledge

Resistance is the property of an electrical conductor, to work against the flow of the current and change some of the electrical energy into heat. The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit, according to Ohm's law. The unit of resistance is the ohm and the amount of resistance that limits the passage of current to one ampere when a voltage of one volt is applied to it happens. The standard abbreviation for electric resistance is R and the symbol for ohms in electric circuits is the Greek letter omega, Ω. To find the value of resistance, the equation

Resistance = Voltage / Current is used.

The resistance of an object is determined by a property of the substance of which it is made of, known as the resistivity and by the length and cross-sectional area of the object. Also, the temperature can determine the resistance of the resistor. At a given temperature, the resistance is proportional to the object's resistivity, length and inversely proportional to its cross-sectional area. Usually, a material's resistance increases with the rise in temperature as the voltage going across the wire has to avoid the resistor’s atoms more. This produces more energy causing plenty of heat.

The term resistance is also used when the flow of a fluid or heat is blocked. The forces of friction provide the resistance to the flow of a fluid in a pipe and insulation provides thermal resistance that reduces the flow of heat from a higher to a lower temperature. It is not just the resistor that causes resistance in the circuit, as any component in the circuit causes resistance. The 3 variables are the length, diameter of the wire, the material the resistor is made out of and the temperature of the wire. The length of the wire will make a difference because there will be more atoms for the current to pass through so there will be more resistance in the wire. The diameter of the wire will make a difference as the thicker the wire, the easier the current will be able to pass through it, as there is more room within the wire. The material the resistor is made out of will also make a difference as if the wire has a high density, there will be more atoms in the wire causing high resistance, but if the wire has a low density, the atoms are less so there are so the is less resistance. The temperature will make a difference as if the temperature is high, there will be plenty of kinetic energy in the resistor and the atoms will be moving about. The current will find it hard to pass through the wire with atoms moving about so there will be more resistance. For the experiment, the variables except the length will be kept the same, as it will make it a fair test.

The factors I can change are:

Length – The longer the extent of the wire the more the electrons will have to journey along it, making the resistance higher. Because of this the length enhancement should be proportional to resistance increase.
Thickness - If the wires width is enlarged the resistance will lessen. This is since the boost in the room for the electrons to journey through. Because of this improved room among the atoms there should be fewer collisions.
Temperature – Resistance creates heat, but heat also amplifies resistance. This is since the atoms in the ...

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The factors I can change are:

Length – The longer the extent of the wire the more the electrons will have to journey along it, making the resistance higher. Because of this the length enhancement should be proportional to resistance increase.
Thickness - If the wires width is enlarged the resistance will lessen. This is since the boost in the room for the electrons to journey through. Because of this improved room among the atoms there should be fewer collisions.
Temperature – Resistance creates heat, but heat also amplifies resistance. This is since the atoms in the wire vibrate more due to their increased energy. This causes more collisions with the electrons as the atoms vibrate into the path of the electrons. Resistance is caused by collisions with atoms in the wire and
Type of wire used - The type of material will affect the amount of free electrons, which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are supplementary or bigger atoms then there must be additional electrons accessible. If the material has an elevated amount of atoms there will be higher numbers of electrons producing an inferior resistance because of the increase in the number of electrons.

As I am going to need to use several different lengths of wire in this experiment, it would be more efficient to use a long piece of wire attached to a meter rule, so I can adjust the crocodile clip and have the measurements displayed already. To test the resistance of the different lengths of wire, the crocodile clips are placed along the wire, so that the desired length is between the clips.

I have decided to use length of the wire as my variable.

Fair Test

To ensure that this experiment is performed as justly as possible I have come up with a list of things that need to be constant through out the experiment. To get as accurate results ass possible.

I will try to measure the wire as accurately as possible so it is as near to the 10cm as possible.

I will ensure the voltage is the same, during the experiment. Resistance is affected by heat, and one of the products of resistance is heat. So I will make sure that I let the apparatus cool down for about a minute in between each individual experiment. The heat causes the atoms in the wire to vibrate quicker causing higher resistance.

Predictions

I predict that as the wire gets longer, the resistance will increase. My reasons are that as the wire gets longer the more times the free electrons will crash into the other free electrons, the particles in the metal. So additional energy will be lost in those collisions as heat. I also think that as the length of the wire doubles the resistance will double. And as the length triples the resistance will triple too. This is because by doubling the wire you double the amount of collisions that will occur, therefore doubling the amount of energy lost in those collisions.

Preliminary work

Results

I didn’t experience any problems with the preliminary work. I kept everything the same in the final experiment

dissimilar materials have different resistances because the materials’ atomic structures are different so several metals have low resistances and some have high resistances. thus it is significant to maintain the material the same all the way through the experimentation . If different materials are used throughout the examination, it will influence the results. for instance if occasionally copper is used and occasionally nichrome is used, the outcome where nichrome is utilized will be of a higher resistance because of the material. Throughout the experiment nichrome will be used.

Method

The apparatus was set up, as shown in the diagram below. Then we repeated the experiment 3 time, changing the voltage each time using 2, 4 and 6 volts. An average was calculated to make it a fait test. We marked on the wood supporting the wire, the measurements with intervals of 10cm as they were not already recorded. We recorded dimensions with spaces of 10cm from 10cm up to 100cm. The crocodile clips were adjusted on the wire, according to the desired length. After every reading the power pack was switched of to allow it to cool down. We recorded the results in a table.

Equipment

Nichrome wire
Power pack
6 wires
Ammeter
Volt meter
Crocodile clips
Meter rule

Results

Conclusion

From my graph I can see clearly that as the length of the wire increases so does the resistance. My line is not entirely straight probably due to a few mistakes on my behalf, but as you can see it is almost directly proportional. And as Ohm’s law states: “the current through a metal conductor is directly proportional to the voltage across its ends, as long as all other conditions are constant”, so that is what I expected to be the case, and it was, as we were changing the length.

As I also predicted, when you double the length of the wire the resistance doubles also. Because there double the amount of collisions and double the resistance. Likewise, if you triple the wire length there should be three times the amount of collisions and three times the resistance.

So my results support my prediction well. They have shown clearly, and with only a few irregularities, that as the length of a wire increases, so does the resistance. The graph is a clear, steady pattern visible both in the results table and in the graph. You can see that for 0.4m the resistance is C. 5.6Ω, and for 0.8m the resistance is C. 11.5Ω. This is nearly double the resistance. Also, at 0.3m the resistance is C. 4.3Ω, and at 0.9m the resistance is nearly 3 times that at 13.4Ω.

Evaluation

I think that overall the experiment went very well. The only major mishaps were that the results weren’t directly proportional when they should have been. I think this may have been because the wires overheated more at some points than at others. The crocodile clips are also fairly wide and large in comparison to the actual wire which is small, so it would be impossible to get completely accurate results for that reason. Also while measuring the intervals with the meter rule, I may have measured a few millimeters of and therefore made inaccurate.

I think that by looking at the graph you can see that my results were fairly accurate, as they were nearly all in a constantly straight line. I also followed all the instructions carefully and for that reason also I believe that they were very accurate. Although the results weren’t completely straight, there weren’t any results that were completely of the mark, with perhaps the exception of 50cm 7.69ohms. To improve the experiment I would like to use thicker wire to stop it from heating so quickly, and also so that the crocodile clips could be paced more accurately on it. I also think that the voltages should have been taken at intervals of 1 volts as that would have been more accurate than with intervals of 2 volts. To increase the reliability of the results we could also increase the length intervals. Anything under 5cm would be too small so 5cm intervals would be more appropriate.

Julie Davies 10H