Resistance of wire.

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Physics-Coursework

Resistance of wire.

Planning

Introduction:

Resistance is a force, which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires are either very thin or very long. Resistance is measured in ohms. George Ohm came up with a rule for working out the resistance of a circuit:

R=V / I

V : Volts
I : Current
R : Resistance

Aim:

To investigate how the electrical resistance of a wire changes in relationship to its length.

The resistance of a wire depends on certain factors.

· Length of wire

· Temperature at which wire is kept

· The material of wire

· The potential difference or voltage

· Humidity

· Cross sectional area.

· Voltage across circuit

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

I have decided to investigate how the length 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 length 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.

Key factors:

In this experiment we will only change one factor, the length of the wire. Fair test: in this experiment we are only changing one factor – the length of the wire, the factors that we are going to keep the same are as follows:

  1. We must keep the surrounding room temperature the same or the particles in the wire will move faster (if the temperature is increased) and this will therefore have an effect on the resistance.

  1. The cross sectional area of the wire must be kept constant throughout as well. The cross sectional area is a factor that effects the resistance.

  1. The material of the wire must also be kept the same as different materials have different conductivity. The last two factors will be kept the same by using the same wire all of the way through the experiment.

  1. The voltage that passes through the wire is to be kept the same. If this is changed the temperature of the wire might change in a way that is not constant making the results more confusing.

Apparatus:

Plan:
1. Connect circuit as shown in the diagram.
2. Adjust rheostat until the ammeter reads 1V
3. Record Amps and length of wire.
4. Repeat the experiment with the following lengths of wire, connected between the two crocodile clips:
- 25 cm

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- 50 cm

- 75 cm

- 100 cm

-125 cm

-150 cm

Safety:

During the experiments the wire may get very hot. To prevent this I will use a low voltage and I will try not to touch the wire.

Preliminary Work:

To make sure our chosen factor and lengths are suitable for this piece of coursework we are going to carry out a few preliminary tests. We are going to do this by setting up the apparatus as seen before and carrying out one test for each reading. We do this to make sure our chosen lengths ...

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