Physics AT1 Kobir Ali

To find out how the resistance of a wire changes depending on its thickness.

Preliminary WorkCurrent (A)Voltage (V)Resistance (?)0.040.56140.050.



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070.182.1411.890.242.7511.46TheoryElectric conductors are materials that can carry an electric current. The best conductors are metals, because in these the electrons can move freely through the material, carrying the current.

In this experiment the conductor is going to be a metal wire. As the electrons move, they strike the atoms and make them vibrate; this interferes with the current flow and causes the materials to heat up (kinetic energy). This is electrical resistance.

Good conductors have low resistance (e.g. copper).Electrical resistance measures how difficult it is for an electrical current to flow through a material. We can think of current being carried by electrons; if they were completely free to flow along, there would be no electrical resistance. However, the electrons collide with each other and with the atoms in the material and lose energy. So more energy has to be supplied to keep the current flowing to push the electrons through the material. This extra energy is called the voltage.

The resistance of a wire can be affected by the following four factors;� Length of wire- The longer the wire the higher the resistance,� Temperature- Resistance can be affected by the temperature,� Thickness of the wire (cross sectional area) – Less resistance for wire of larger cross sectional area.� Type of metal- Gold and silver have low resistances.The resistance of a wire can be calculated by using the following equation;Resistance= VoltageCurrentIn our experiment we are going to investigate the difference in resistance of Various thickness wires.

Apparatus – Batteries- Voltmeter- Ammeter- Variable Resistor- Five different thickness wires- Connecting wiresDiagram-Method-1- Set up apparatus as shown on diagram.2- Get five different thickness of wires.3- Measure the thickness of each wire, three times to get an accurate average.4- Attach the wire to a meter ruler, measure the length of the wire to 60 cm.

5- Connect one of these wires where specified on the diagram.6- Take readings from both the voltmeter and ammeter and record the readings on a table.7- Change the position of the resistor (Variable resistor) and take another set of readings.8- For each different thickness wires change the position of the resistor 5 times and record the readings.PredictionI predict the thinner the wire used in the experiment the more resistance there will be, due to the fact that the electrons will have a restricted amount of space, which will therefore increase the amount of times the electrons will have to bump into each other to flow along with the current, hence increase the resistance and also the current will be small.

If the wire is thick, more electrons can flow more quicker, with the minimum amount of resistance. If the voltage is low, the current will be high because many more electrons can flow through a given point in a circuit.ResultsMeasurements Of Thickness Along Each WireSWG123Average240.550.580.550.56300.290.



191-SWGVoltage(V) /Current (A)Position Of Resistor1234524voltage0.140.510.81.181.35current0.090.







22-3-Position Of Resistor Voltage / Current (Resistance(?))SWG12345Average241.551.591.531.551.591.564304.885.





512.476ConclusionFrom our results we can clearly see that the thicker wire used in our investigation had the least resistant. This is because more electrons can flow without bumping into each other as much, therefore the resistance is low, the more electrons that pass through the wire at any given point increases the current as it is shown on our result table 2.E.g.Cross section of a thick wireMore current flowIn this example we can see that more electrons can go through a wire at one time with less resistance. If we had a thin wire and made it double the thickness as it started off, the resistance is halved.

E.g.Cross section of a thin wireLess current flowAs we went through all the other SWG’s of wire (from thick to thin),We found that the resistance increased when we got down to the thinner wires. This is due to the fact that that the electrons had to always bump into each other to move along the current, therefore the resistance is increased. The current is also low because only a minimum number ofelectrons can go through a given point in a circuit therefore the voltage is increased.EvaluationWhen we first carried out this investigation our results went horribly wrong. Firstly because we somehow managed to put the voltmeter in the wrong place, this gave us ridiculous results.

Secondly, to give us reasonable results we had to have our wires the minimum of 50 centimetres, we made them 20 centimetres!The second time we carried out this experiment; we corrected our mistakes and got a better set of results. But I don’t think these result were that reliable due to the fact that that each wire did not have the same diameter all the way along the 60 centimetre length.


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