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# The aim of this investigation is to investigate the factors affecting the resistance of a wire.

Extracts from this document...

Introduction

## Aim

The aim of this investigation is to investigate the factors affecting the resistance of a wire.

## Background Information

As the electrons in an electric current move around a circuit, they bump into the atoms in the wires through which they pass. Atoms of different elements slow down the electrons by different amounts. For example, electrons pass easily through copper wire but much difficultly through tungsten or nichrome wires. We say that copper has a lower resistance than nichrome or tungsten. This is why copper is used for the connecting wires and cables in electrical circuits. Electrons collide with atoms in the wire that vibrate more quickly. This causes the wire to warm up. If the resistance is high and the current is large, the wire may get red hot. Conductors like this, which provide a high resistance, are called resistors. Resistors vary the current in a circuit. The resistor that I will use in my investigation is called a rheostat. Some resistors obey the Ohm’s law. A German scientist, Georg Ohm, investigated the resistance of various metal conductors. The unit that we use for resistance is called the Ohm in honour of Georg Ohm. The symbol for the ohm is Ω, so five ohms is written as 5 Ω.

The equation to measure the resistance (Ohm’s law) is:

R = V                    Resistance = Voltage (Volts)

I                                         Current (Amps)

The more resistance there is the more electrical energy is converted to other forms of energy, such as heat and light energy. Hence, raising the temperature because the electrons in the substance are colliding, causing kinetic energy.

Current is proportional to the voltage, providing that the temperature stays constant. When temperature is constant the current is proportional to the electric field.

Middle

1

1.9

Constantan

22

125

40

2

1.9

Constantan

22

125

40

3

1.9

1.9

2.1

Constantan

22

125

50

1

1.9

Constantan

22

125

50

2

1.9

Constantan

22

125

50

3

1.9

1.9

2.1

Constantan

22

125

60

1

1.8

Constantan

22

125

60

2

1.8

Constantan

22

125

60

3

1.8

1.8

2.2

Constantan

22

125

70

1

1.8

Constantan

22

125

70

2

1.8

Constantan

22

125

70

3

1.8

1.8

2.2

Table 2 (Varying length) – SWG 26

 Material SWG Thickness(Diameter in g) Length (cm) Reading No Current (A) Average (A) Resistance (Ω) Constantan 26 125 10 1 2.1 Constantan 26 125 10 2 2.1 Constantan 26 125 10 3 2.0 2.1 1.9 Constantan 26 125 20 1 1.9 Constantan 26 125 20 2 2.0 Constantan 26 125 20 3 1.9 1.9 2.1 Constantan 26 125 30 1 1.8 Constantan 26 125 30 2 1.8 Constantan 26 125 30 3 1.8 1.8 2.2 Constantan 26 125 40 1 1.7 Constantan 26 125 40 2 1.7 Constantan 26 125 40 3 1.7 1.7 2.4 Constantan 26 125 50 1 1.6 Constantan 26 125 50 2 1.6 Constantan 26 125 50 3 1.6 1.6 2.5 Constantan 26 125 60 1 1.6 Constantan 26 125 60 2 1.5 Constantan 26 125 60 3 1.5 1.5 2.7 Constantan 26 125 70 1 1.5 Constantan 26 125 70 2 1.5 Constantan 26 125 70 3 1.5 1.5 2.7

Table 3 (Varying Length) – SWG 28

 Material SWG Thickness(Diameter in g) Length (cm) Reading No Current (A) Average (A) Resistance (Ω) Constantan 28 125 10 1 2.8 Constantan 28 125 10 2 2.8 Constantan 28 125 10 3 2.7 2.8 1.4 Constantan 28 125 20 1 2.5 Constantan 28 125 20 2 2.5 Constantan 28 125 20 3 2.6 2.5 1.6 Constantan 28 125 30 1 2.3 Constantan 28 125 30 2 2.4 Constantan 28 125 30 3 2.4 2.4 1.7 Constantan 28 125 40 1 2.2 Constantan 28 125 40 2 2.0 Constantan 28 125 40 3 2.1 2.1 1.9 Constantan 28 125 50 1 1.9 Constantan 28 125 50 2 1.9 Constantan 28 125 50 3 1.9 1.9 2.1 Constantan 28 125 60 1 1.8 Constantan 28 125 60 2 1.8 Constantan 28 125 60 3 1.8 1.8 2.2 Constantan 28 125 70 1 1.7 Constantan 28 125 70 2 1.7 Constantan 28 125 70 3 1.7 1.7 2.4

Table 4 (Varying SWG/Thickness) – Length 10cm

 Material SWG Thickness

Conclusion

It was beneficial that I took a range of readings because just in case there was a loose connection and I did not recheck it, my results would be incorrect. Therefore, it was a good idea to take three readings of each result. This way I could see if I made a mistake. My method was quite suitable. However, to improve this I could have put the piece of wire at the end of the clip so that the accuracy of the length would not be varied or changed.

To extend my investigation another experiment can be devised. Due to the fact that at room temperature the thermistor has a high resistance, its resistance falls when it is heated. It gives a lower resistor, a larger share of the battery voltage. This in turn will make the bulbs light up.

Thermistor (e.g. TH3)

By putting the thermistor at the top of the potential divider the total resistance will fall because the temperature will rise. This will mean that the voltage will get bigger. If this further extended improvement proves correct that means that the bulb will light up. We will know if this works by calculating the resistance and plotting a graph, which should produce a curved graph for a thermistor.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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