Resistance of a Wire

Introduction

The resistance of a wire depends on certain factors. Some of these variables are listed below:

• Length of wire

• Diameter or thickness of wire

• Temperature at which wire is kept

• The material of which wire is made out of.

• The potential difference or voltage.

• Humidity

• Cross sectional area.

• Voltage across circuit

All these factors will have to be kept constant except the diameter of the wire whilst doing the experiment to ensure that the investigation is a fair test.

I have decided to investigate how the diameter of a wire affects its resistance because other factors such as temperature are hard to control or vary. There is not a large enough range of materials to investigate how materials affect the resistance of a wire. The way in which the diameter of a wire affects the resistance is an efficient experiment to do. A graph can be plotted easily, there is a large range of results and the results can be recorded easily.

Variables

The investigation is to investigate the resistance when the diameter has changed. In order for the investigation to be a fair test, all other factors or variables should be kept constant. The investigation has to be done in a fair manor otherwise the results would be inaccurate and the conclusion would be incorrect. The variables, which must be kept constant, are:

1) Temperature when the temperature of a metal increases the resistance of that metal increases. This is because when the temperature increases the atoms of the metal vibrate more vigorously because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the atoms, which are in their pathway. This increases the amount of collisions therefore there is more resistance. However it is hard to keep the temperature exactly the same as the room temperature might change from day to day. It is essential to use a low voltage because it means a low current that will not heat up the wires. If a high voltage is used the energy would be in form of heat which would make the experiment unfair. The investigation will be done at room temperature. The temperature cannot be investigated because it is hard to control the range of temperature needed without the correct apparatus.

2) Length of wire The larger the length of the wire, the larger the resistance. This is because there are more atoms from the metal so there is more chance that the electrons would collide with one of the atoms therefore there is more resistance. It is important to keep the length of the wire the same each time otherwise it could not be certain which variable is changing the resistance. The length of wire will be 50cm throughout the investigation. Electrons have a longer distance to travel so there are more collisions .The length of the wire will make a difference to the resistance. This is because when you have a long wire, the electrons have to squeeze together for longer to be able to pass through the wire than they do in order to be able to pass through a short wire. I predict that the longer the wire, the greater the resistance. If I had a 30-cm wire and a 60-cm wire, the 60-cm wire would have a resistance twice that of the 30-cm wire.

3) Type of material different materials has different resistances because the materials’ atomic structures are different so some metals have low resistances and some have high resistances. Therefore it is important to keep the material the same throughout the experiment unless a different material is used to check if the conclusion or theory works for all materials. If different materials are used throughout the investigation, it will affect the results. For example if sometimes copper is used and sometimes nichrome is used, the results where copper is used will be of a low resistance because of the material and not because of the diameter of the wire. Throughout the experiment Constantine and nichrome will be used. Constantine is used to make sure my conclusion works for all materials. The type of material will affect the amount of free electrons that are able to flow through the wire. The number of free electrons depends on the amount of electrons in the outer shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase of the number of electrons. If the particles in the material are tightly packed