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# My aim is to find out what affect a length of a wire has on its resistance. The resistance will be measured by finding out the current and the voltage travailing through a wire at variable lengths.

Extracts from this document...

Introduction

10B

## Planning

Aim

My aim is to find out what affect a length of a wire has on its resistance. The resistance will be measured by finding out the current and the voltage travailing through a wire at variable lengths. I shall use 11 different lengths of wire so that I have a good range of readings and will be able to plot a line of best-fit graph from the results. The lengths will range from 10 cm to 100 cm and will have a gap of 10 cm between each length of wire so that for example I will have one wire with a length of 10 cm and the next smallest length of wire as 20 cm. I shall measure the lengths in centimetres as I want the divisions between the results clear and I believe that it will be easier to ensure that the wire is a precise number of centimetres. I am starting at 10 cm, because any length below that may be unsafe.

## Background knowledge

Resistance is the opposition to the flow of electrons. As the electrons flow through the wire they bump into atoms. When they bump into an atom, the electron looses some energy and slows down.

Middle

• One possible risk is that if I put too much current through the wire the wire will become hot and I could burn my finger from the heat. Also it may affect the resistance of the wire or blow a fuse in the power supply.
•  Another risk is that if my resistance wire is too short a short circuit or similar danger may occur; therefore my smallest length of wire shall be 10 cm in order to eliminate this risk.

## Planned Method

1. Measure the wires width at different parts of the wire to check that it has a constant width
2. Set up the above circuit connecting the wire into the circuit using crocodile clips at 10 cms apart using a ruler.
3. Turn on the voltmeter and the ammeter and make sure that both have a positive reading.
4. Making sure that variable resistor is at the begging take the first reading on the ammeter and the volt meter and record these results
5. Now move the variable resistor along and take the new readings
6. Continue to move the variable resistor until you get at least ten readings

Conclusion

/tr>

## 30cms

 Current Voltage Resistance 0.07 0.20 2.857… 0.08 0.22 2075 0.09 0.25 2.777… 0.10 0.28 2.800 0.12 0.33 2.750 0.14 0.38 2.714… 0.16 0.47 2.937… 0.24 0.67 2.791… 0.34 0.94 2.764… 0.37 1.02 2.756…

40cms

 Current Voltage Resistance 0.06 0.28 4.666… 0.07 0.31 4.428… 0.08 0.33 4.125 0.10 0.36 3.600 0.11 0.43 2.727… 0.13 0.51 3.923… 0.17 0.67 3.941… 0.22 0.86 3.909… 0.28 1.12 4.000 0.31 1.27 4.096…

Resistance Calculation

Examples-

First set of equipment: Length of wire= 10cm, Voltmeter reading= 0.15V, Ammeter reading= 1.40A

Formula: Voltage= Resistance    0.15V = 0.11 Ohms (2d.p)

Current                          1.40A

Therefore the resistance of the wire was 0.11 Ohms, with the wire length at 10cm and using the first set of equipment.

Second set of equipment: Length of wire= 60cm, Voltmeter reading= 0.86V, Ammeter reading= 0.46A

Formula: Voltage= Resistance    0.86V = 1.87 Ohms (2d.p)

Current                          0.46A

Therefore the resistance of the wire was 1.87 Ohms, with the wire length at 60cm and using the second set of equipment.

Third set of equipment: Length of wire= 90cm, Voltmeter reading= 0.94V, Ammeter reading= 0.13A

Formula: Voltage= Resistance    0.94V = 7.62 Ohms (2d.p)

Current                          0.13A

Therefore the resistance of the wire was 7.62 Ohms, with the wire length at 90cm and using the third set of equipment.

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