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Resistance of wires.

Extracts from this document...


Resistance of wires

Matthew Hampton


Physics coursework.

Planning My Investigation

Scientific Knowledge and Background

Metals are made up of metal atoms. Metal atoms bound to other metal atoms in a piece of metal or metallic bonding holds an alloy together. This type of bonding is different from atoms in covalent or ionic bonding as in metallic bonding the atoms do not hold onto their electrons strongly, in fact the atoms share the electrons in a sea of electrons, where they are free to move about and are not fixed to one particular atomic nucleus. This is the reason that metals can conduct electricity so well.

Ohm’s law: Experiments show that for metallic conductors, so long as their temperature does not change, V/I always has the same value when V (voltage, measured in volts) is varied and the corresponding value of I (current, measured in amps) is found. That is, the resistance of a metallic conductor is constant whatever the voltage applied. Hence V/I is a constant. This means, for example, that doubling V doubles I, and so on.

The current through a metallic conductor is directly proportional to the potential difference across its ends if the temperature and other physical conditions are constant.

Current is the flow of electrons round a complete circuit. Voltage is the driving force that pushes the current round. Resistance is anything in the circuit that slows the flow down. If you increase the voltage then more current will flow and if you increase the resistance then less current will flow.

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I predict that as the length of wire tested in the circuit gets longer, so the calculated resistance will increase. I also predict that the relationship between length and resistance will be a straight line with a 45-degree angle, so that when the wire length increases by a factor of 2, so the resistance will double. This is because I think the unit resistance of Constantan wire is constant, as long as all other variables except length are kept the same.

Main experiment

Apparatus used:


Amp meter


Power pack

Crocodile clips

Constantan wire


Metre rule


Exercise book to record results in

Circuit Diagram


I constructed a circuit as shown in the diagram above, using the apparatus listed above. The variable in the circuit was the length of the piece of wire, and I measured the length of the piece of wire used, the voltage and the current flowing through the circuit during each experiment. The piece of Constantan wire was laid along a ruler. A crocodile clip was placed at 0cm and the length of wire to be included in the circuit was determined by connecting a crocodile clip to the wire at exactly the correct place. The voltage was set at 4 volts. The voltmeter was connected in parallel to the wire and the ammeter in series. From the voltage and amps reading I calculated the resistance of the piece of wire. I performed each experiment three times, using 8 different lengths of measured wire. I averaged the results for each length of wire to increase the reliability of the results. I then plotted a graph of my results.

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I do not feel that I could have improved the method or the equipment for this experiment and that the results obtained were accurate and reliable. The experiment was fair and safe. The results obtained were completely in keeping with both my prediction and the outcome I expected from my reading of background information and scientific theory.

        Although my experiment proves that there is resistance in wires there are also other experiments that could be done to learn about the resistance of wires, for example, a ‘Micrometer screw gauge’ this measures very small lengths such as the diameter of a wire. So the thickness of wire could be tested to learn about the resistance in wires.

 Also I could test all the factors mentioned in the planning of my investigation such as the temperature and the Chemical composition of the wire. I could use several different types of wires and I could use different temperatures of wires to see if those factors affect the resistance of wire.

Even though I haven’t done these experiments for the different factors I would expect the same results and the same out come proving that Wires have resistance.

To gather my information I used ‘ Physics for today and tomorrow’ by Tom Duncan

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