An experiment to investigate the factors which affect the resistance in a wire.

Topics: Electric charge, Electricity, Electron Pages: 6 (1674 words) Published: January 26, 2003
An experiment to investigate the factors which affect Resistance in a wire

What is resistance?

A potential difference (V) applied across a wire of length (l), there is in the conductor, an electric field (E). In this electric field the free electrons are not however under continuous acceleration (Ee/m). This is because they repeatedly collide with the moderately massive vibrating atoms losing their kinetic energy. The vibrating atoms having gained this kinetic energy now vibrate more. The resulting increase in the average vibration kinetic energy is rise in temperature.

Movement of charge carriers in any medium must necessarily be subject to such collisions causing loss of kinetic energy and generating heat in the medium. This heating of the medium due to the passage of charge carriers is a general property of all materials and is due to the resistance offered by the material to the flow of charge. The resistance of any material is measured as the potential difference required per unit current in that material. Hence the resistance (R) is determined as:

Where (V) is the applied potential difference and (I) the current in the material It should be noted that all materials require to have a potential difference applied in order to maintain an electric current in the material. Consequently all materials have resistance. Some materials become more heated than others despite the same rate of flow of charge.

Energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires in the circuit are very thin and very long. For example, a filament in an electric light bulb is extremely thin and incredibly long. Due to the resistance, energy is given out as heat and light. Numerous household appliances, such as electric heaters, hair dryers, toasters, oven and electric fires, use a high resistance wire in their elements so that heat is given out.

There are four different factors, which affect the resistance in a wire:

1. Thickness - thin wires have more resistance than thicker wires, because there is not as much space inside the wire, which means the electrons have a lot more resistance inside the thinner wire than the thicker wire.

2. Length - The larger the length of the wire, the larger the resistance. This is because the longer the wire there is more chance that the electrons can collide with more wire particles therefore it creates more resistance. In a longer circuit, it is more of a struggle for electrons to get around the circuit without any collisions. There are many more wire particles (acting like obstacles) to avoid. Electrons cannot increase or decrease speed, but they can collide. They collide with the particles in the wire; therefore fewer electrons are able to flow than in a shorter length wire. 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 are more resistance.

3. The material used - Different materials have 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. 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 together, the electrons will have more collisions and therefore more resistance.

4. Temperature - When the temperature...
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