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# Investigation of the factors that affect the resistance of a wire.

Extracts from this document...

Introduction

Investigation of the factors that affect the resistance of a wire

AIM: To investigate how the length, the cross sectional area and the material of a wire affect its resistance.

PLANNING:

Background information

Metals have a high density of conduction electrons. The aluminium atom for example has three valence electrons in a partially filled outer shell. In metallic aluminium the three valence electrons per atom become conduction electrons. The number of conduction electrons is constant, depending on neither temperature nor impurities. Metals conduct electricity at all temperatures, but for most metals the conductivity is best at low temperatures.

Resistance in electricity is the property of an electric circuit or part of a circuit to transform electric energy into heat energy by opposing electric current. Resistance involves collisions of the current-carrying charged particles with fixed particles that make up the structure of the conductors; this can be seen in the diagram below. Resistance is often considered as localized in such devices as lamps, heaters, and resistors, in which it predominates, although it is characteristic of every part of a circuit, including connecting wires and electric transmission lines.

## Diagram 1: The collisions of electrons with ions in a circuit

Electron

Ion

direction

in which the electron

is moving

Here the electron is going to collide with the ion and so the speed at which it is traveling will decrease and since the electron is one of the current-carrying charged            particles the current in the circuit will decrease.

The spread of electric energy in the form of heat, even though small, affects the amount of electromotive force, or driving voltage, required in order to produce a given current through the circuit. In fact, the electromotive force V (measured in volts) across a circuit divided by the current I (amperes)

Middle

5.32

0.6 meter

0.74

0.20

3.7

1.04

0.26

4.00

1.23

0.32

3.84

1.42

0.41

3.46

1.63

0.45

3.62

1.80

0.48

3.75

3.73

0.4 meter

0.46

0.18

2.56

1.08

0.47

2.30

1.26

0.53

2.38

1.45

0.59

2.46

1.56

0.61

2.56

1.71

0.67

2.55

2.47

0.2 meter

0.59

0.44

1.34

0.94

0.70

1.34

1.11

0.82

1.35

1.36

1.01

1.35

1.58

1.17

1.35

1.81

1.34

1.35

1.35

Results obtained for the manganin wire:

 Lengths of the wire used. V I R V I R V I R V I R V I R V I R Average resistances found from other resistances. 1.0 meter 0.89 0.16 5.56 0.98 0.18 5.44 1.06 0.20 5.30 1.24 0.23 5.39 1.45 0.27 5.37 1.61 0.30 5.37 5.41 0.8 meter 0.87 0.20 4.35 0.99 0.22 4.50 1.06 0.24 4.42 1.24 0.27 4.59 1.45 0.32 4.53 1.61 0.39 4.13 4.42 0.6 meter 0.86 0.26 3.31 0.99 0.30 3.30 1.07 0.32 3.34 1.25 0.38 3.29 1.46 0.44 3.32 1.62 0.49 3.31 3.31 0.4 meter 0.86 0.35 2.46 0.98 0.40 2.45 1.07 0.43 2.49 1.26 0.50 2.52 1.44 0.62 2.32 1.65 0.70 2.36 2.43 0.2 meter 0.88 0.77 1.14 0.98 0.86 1.14 1.05 0.91 1.15 1.25 1.09 1.15 0.24 0.21 1.14 0.37 0.32 1.16 1.15

Results obtained for the copper wire:

 Lengths of the wire used. V I R V I R V I R V I R V I R V I R Average resistances found from other resistances. 1.0 meter 0.16 0.18 0.89 0.18 0.24 0.75 0.17 0.30 0.57 0.68 1.20 0.57 0.17 0.50 0.34 0.11 0.18 0.61 0.62 0.8 meter 0.12 0.20 0.60 0.14 0.26 0.54 0.15 0.31 0.48 0.22 0.51 0.43 0.13 0.40 0.33 0.19 0.61 0.31 0.45 0.6 meter 0.10 0.17 0.59 0.06 0.23 0.26 0.07 0.26 0.27 0.70 0.30 0.38 0.17 0.52 0.33 0.28 0.96 0.29 0.35 0.4 meter 0.04 0.18 0.22 0.05 0.25 0.20 0.09 0.35 0.26 0.15 0.40 0.38 0.09 0.41 0.22 0.16 0.65 0.25 0.26 0.2 meter 0.04 0.18 0.22 0.11 0.94 0.12 0.07 0.31 0.23 0.13 0.46 0.28 0.08 0.39 0.21 0.12 0.54 0.22 0.21

Results obtained for the nichrome wire:

Conclusion

During this write up I calculated the resistivities of the metals that I used, I looked in an A-level physics book for the values it gave for the resistivities of those metals in order to compare them with the values I found. The following are the resistivity values that I found in the book:

• The resistivity for constantan is 49 * 10-8
• The resistivity for manganin is 44 * 10-8
• The resistivity for copper is 1.7 * 10-8
• The resistivity for nichrome is 110 * 10-8

It can be seen that my resistivity values calculated in the ANALYSIS SECTION are very close to those found in the book. This further emphasises my opinion that my results are accurate enough to draw conclusions.

Further Work

To improve the experiment in order to provide additional and more reliable evidence for a conclusion I would carry out the experiment using additional different metals to see how their resistances would change as their lengths and cross sectional areas were varied. Such examples of these metals could be for example titanium, silver, steel, brass etc…

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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