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The factors that affect the resistance of a wire

Extracts from this document...

Introduction

The factors that affects the resistance of a wire        Tom Pattle

By Tom Pattle

Contents

Plan - Pg 4 ~ 11

Introduction - Pg 4

Background Knowledge – Pg4  ~ 7

Prediction – Pg 8

Method – Pg 9  ~ 11

Analysis – Pg 14 ~ 16

A graph to show the resistance of a wire at room temperature – Pg 16a

A graph to show the resistance in a wire when kept at a constant temperature – Pg 16b

A graph to show the resistance in a wire when at room temperature and kept at a constant temperature – Pg 16c

Evaluation – Pg 17 ~ 18

References – Pg 19

Plan

Introduction

The experiment that will be carried out is about the factors that affect the resistance of a wire using Nichrome 32SWG. When a current of 0.10 amps is passed through this wire, a resistance will form. The voltage will be measured, and using the following equation the resistance will be calculated:

Resistance = voltage ÷ current

(this equation is explained further on page  5)

By finding the resistance when the Nichrome is at different lengths and when the temperature is kept constant will show us the factors that affect the resistance of a wire.

Background Knowledge

For this experiment to be successful, one of the four factors that effect resistance must be included in the experiment:

As the length of the wire increases, the resistance increases.

Middle

The voltage travelling across the wire will then be recorded, and the power unit will be switched off.

The same process will then be repeated for 20cm – 100cm

Experiment Two

1. The Nichrome wire will be measured at 10cm and connected to the circuit via the crocodile clips, it will then be placed in the beaker of water,
2. The power unit will be switched on,
3. The variable resister will be set to the correct current by the reading on the ammeter,
4. The voltage travelling across the wire will then be recorded and the power unit switched off.

In order for the experiments to be carried out safely the following safety precautions must be adhered to:

• The power unit must be turned off before touching any of the other pieces of equipment, and,
• Eye protection must be worn at all times.

Ten results will be taken with the wire increasing in length by 10cm each time; this will be repeated three times for best results and in the case of a result being anomalous.

Fair Test

To make sure the two experiments are fairly undertaken, the following must be done:

• When doing experiment one the room temperature must not be changed dramatically – because temperature effects the resistance of the wire,
• The current must be kept the same – so that each length of wire has the same amount of amps passing through it because  The same amount of amps will also be used for experiment two,
• The power unit must be kept at the voltage (2 volts) – so that the current can be kept the same,
• The amount of water in the beaker must be kept the same for experiment two – so that each length of wire is put in the same amount of water,
• The temperature of the water must be kept constant (21 °C) – so that each length of wire is tested at a constant temperature.
• The Nichrome 32SWG must not touch itself during the experiments – because it will affect the resistance of the wire.

Conclusion

The wire could be supported by clips to stop it touching itself,A temperature reading could be taken regularly and noted to see if temperature was approximately the same. If the temperature was not the same, you could postpone the experiment until it was,Measure to water level more precisely using a burette,A more sensitive resistor could be used to keep the current the same (e.g. rotary resister).

These more precise methods of carrying out the investigations would overcome the main problems to give a better table of results. Repeating the results for a 4th time could also help to improve the reliability and also dispose anomalous results.

There are also some other experiments and techniques that could be used to improve and extend the assignment:

1. The results could be taken over a wider range by increasing the length of wire,
2. A number of different experiments could be carried out were the other three factors that affect the resistance of wire were studied. Cross-sectional area, different materials, diameter.
3. Also, to extend the coursework, instead of changing the length of the Nichrome wire the current could be changed.

References:

• EDEXCEL revision guide
• Class notes
• Coursework hand-outs

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