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Investigate the relationship between the resistance of a wire and its length.

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Introduction

07/05/07

Practical Physics No.

Name: Arwin Kandhai

Class:5s

Aim:

The aim of this is to investigate the relationship between the resistance of a wire and its length.

Apparatus:

Ammeter, voltmeter, connecting wires, power supply, potentiometer, jockey, variable resistor

Prediction:

I think that the longer the wire, the more resistance, as preliminary results would suggest this. This would be as electrons lose some of there energy when they collide.
I will have to keep the voltage low to minimise resistance. This is due to kinetic theory, the more voltage, the hotter the wire, the faster moving particles therefore the more energy lost through collisions. The graph will be a straight line through the origin, because current is proportional to the voltage, hence the resistance I=V is constant.

I also predict that resistance will be proportional to length, this is because I predict a length of wire 10cm long will have twice as many collisions as a wire 5cm long.

Safety:

-Handle the power supply carefully.
-I am going to only use a voltage of four volts so the wire will not burn.
-Be careful when touching the wire, as it may be hot.

...read more.

Middle

Set up the apparatus as shown in the diagram above.Adjust the variable resistor to allow the smallest possible current to flow in the circuit.Note the ammeter reading (I) and the voltmeter reading (V).Adjust the variable resistor to allow a larger current to flow in the circuit. Again note the values of I and V.Repeat the above at least 5 times and record the readings.
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Conclusion


Power supply, Voltmeter, Wire, Meter ruler

Instead of connecting the voltmeter to the main circuit I would connect it to the wire, which is being tested. I would do this so that the voltmeter is measuring the voltage of just the wire being tested and not the wires of the main circuit as well.
To also improve on my results I would use a digital voltmeter instead of an analogue meter. I would do this because a digital voltmeter is a lot more accurate than an analogue because if the needle in the analogue voltmeter is bent then the readings given off will be false whereas a digital voltmeter does not rely on a needle or any other manual movements.

The next modification I would make would be to use pointers instead of jockey; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire.
As well as making these modifications I would also improve my Investigation by testing the same wire but different widths of that wire. I would do this to expand on my Investigation.

...read more.

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