What effects resistance through a wire?

GCSE Science coursework- Nick Brooks 10 AM

Introduction- Resistance

Electricity passes through all the components of a series circuit, but the components are not all the same. Some of them allow current to pass easily, whereas others slow the current down. This is called resistance. The more a component resists the flow of electricity or electrons, the lower the current in the circuit will be. Resistance also exists in wires. There isn’t as much resistance in wires as components although there is a small amount. The measurement of resistivity is in Ohms. Ohms go by ‘Ohms law’ which has been explained below.

Ohms law

Physical principle stating that the electric current flowing through a metallic conductor is directly proportional to the potential difference between its ends, as long as the temperature stays the same. The law is named after the German physicist who discovered the relationship in 1827, Georg Ohm. The ratio of the potential difference to the current is called the resistance of the conductor, and is measured in ohms, symbol Ω. A potential difference of 10 V (volts) is needed to make a current of 2 A (amps) flow through a conductor with a resistance of 5 Ω. In symbols, V = I R, where V is potential difference, I is current, and R is the resistance. Ohm's law can be restated thus: the resistance of a metallic conductor is constant as long as the temperature stays the same. According to Ohm's law, as the potential difference is increased a greater current flows. However, some materials put up more resistance to the flow of current than others, which is important in designing electrical equipment. Materials such as copper have little resistance to the flow of an electric current and are ideal for wiring electric circuits. Other materials have a higher resistance: the tungsten filament in a light-bulb glows white-hot as the current tries to push electrons through the metal, and energy is released as light and heat.

What I will be trying to find out

In this experiment, I will be trying to find out, what effects resistance through a wire. I will do this by changing various factors which effect resistance, for example: The thickness of the wire, Length of the wire, Type/make of wire and the amount of voltage supplied. All of these factors play a huge part in effecting the resistance through a wire. The two types of wire available are Constantan and Nichrome. Constantan consists of 60% Copper, 40% Nickel and has a resistivity value of 4.8 x 10-6 Ω per metre. Nichrome wire consists ...

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What I will be trying to find out

Variables explained

The different variables I can use are thickness of wire, length of wire, type/make of wire and the amount of voltage supplied. All of these factors do affect the resistance, some more than others. With the thickness of wire, the resistance will be varied by the amount of space the electrons have to pass through the wire, thus differentiating the resistance. With the length of wire, the electrons are spread out in different distances, so again this will affect the resistance. With the type of wire, the resistance values of different wires will vary because of the different elements contained within the wires. With the differentiating voltage, the resistance is going to be varied as to the amount of electrons that are going to pass through the circuit.

What I will vary

For this experiment, I have chosen to vary the type of wire, thickness of wire and the length of the wires. I think that these three variables will sufficient to obtain a good spread of results, to help answer- what effects resistance through a wire?

What I will not change to make a fair test

To ensure that the experiment turns out to be a fair test, I will not change the amount of voltage, which passes through the circuit. Changing the voltage in any way would completely change the results, as more electrons would be in the circuit.

What I will measure

The results I will be collecting for this experiment will be the amount of resistance that each variable produces. I will be measuring the length of wire and noting the thickness. For measuring the resistance, I will be measuring the voltage (volts) and the current (amperes) to which I will work out the resistance by using Ohm’s law which, has been explained on the front page. The theory is: V= potential difference/voltage, I= current and R= resistance. The equation is V= IR, or to find out the resistance: R= V x I.

Safety in the experiment

There are a few aspects of safety, which have to be remembered when using electricity. The first and possibly most important thing to remember when using electricity, is to work in a dry area with no water and to have dry hands. You also have to beware of frayed wires or any defects with the power source. Two safety aspects that are more specific to this experiment are, do not make the wire too short, if it is too short then the wire may heat up and burn away. Also, do not touch the wires when the electricity is on, as they do heat up and there is also a risk of electric shock.

Apparatus

Power pack,
Connecting wires
crocodile clips,
Different wire boards x 4 (Constantan and Nichrome 0.45mm + 0.9mm),
Voltmeter,
Ammeter.

Method

Check wires for damage and use safe area.
Connect up the circuit.
Plug in power pack and switch on.
Record results from voltmeter and ammeter.
Repeat for different wire type, thickness and length
Record results and work out resistance values.
Draw graphs and evaluate experiment.

Prediction

I think that with the wire length variation experiment, the greater the length, the more resistance there will be. I think this because, with a larger length of wire, it would take a longer period of time for the electrons to pass, meaning that more electrons will get caught up thus producing more resistance. In the varying of the thickness of wire, I predict that, the thinner the wire is, the more resistance there will be. I think this because, in a thinner wire, the electrons have a smaller area to pass through so when they rub against the inside of the wire. This produces a build up of heat, which causes a lot of friction. The friction slows the electrons down which causes a greater resistance. With the varying of wire types, I cannot back up any prediction other than the two resistivity values. Going by this, I think that the Nichrome wire will produce more resistance, as it has a higher resistivity value.

Results

Anomalous results

As you can see in the table above, I could not find any results that were far out from the patterns. On the voltage column, a lot of the results did not fit an exact pattern but in the current column, the results were overall fairly accurate. In the overall column, the resistance, the results did stick to a quite regular pattern so it shows that it was a fairly accurate experiment.

What I found out and why

I found out that, with varying the wire length, the longer the wire is, the more resistance, there is produced. This is because, when the wire is longer, the electrons have further to travel. With the voltage not being varied, the electrons spread out along the wire and more of them will get caught along the wire. This would mean that fewer electrons would get through, which causes more resistance.

I also found out that, with varying the wire thickness, the thinner wires produced a lot more resistance than the thick wires. This is because, in the thinner wires, there is less space for the electrons to pass through, half of the amount of space for the thicker wires. With less space, the wires have more chance of colliding with the sides. This would cause a build up of heat and friction. This means that the electrons speed up and begin to collide with each other and the sides, which slows them down. The process of the electrons slowing down is the resistance.

When I varied the type of wire, the results did work in conjunction with the resistivity values given. The higher resistivity value, the Nichrome wire, did produce a lot more resistance, than the Constantan wire, about twice as much. This shows that the Constantan wire is a much better electricity conductor than the Nichrome wire.

Do my results match my predictions?

Yes, my results did match my predictions. I predicted that the thinner wire, the longer wire and the Nichrome wire all produced more resistance. The wire thickness experiment worked correctly and in conjunction with the ‘collision theory.’

Evaluation

As far as experiments go my results were fairly accurate. To get flawless results would be almost impossible as not all elements can be altered to obtain the optimum conditions. I could have got slightly better results but it would be a very small difference to the results I obtained.

The method that I used was the simplest and most accurate way to do the experiment. The only thing that may interfere with the results, is the resistance in the connecting wires, or electricity lost through the crocodile clips. Another thing that might have a small part in making the results impossible is that not exactly the same amount of voltage will come out of the circuit each time.

The only real improvement that I could make to the experiment is to repeat the experiment many times to get averages, which would gain more accurate results. Further experiments I could do to find out other things, which effect resistance through a wire, are to try other varieties of wires to find out what elements have the most resistance. Another experiment to also try is to experiment in different conditions and working environments to see what also effects resistance through a wire.