Method
I will begin by connecting the circuit as shown below in my diagram. I will use the voltmeter to record the voltage. I will use the following lengths of wire to record my results; 100cm, 90cm, 80cm, 60cm, 50cm, 30cm and 20cm. I will use Ohms law resistance in ohms; (R) is equal to volts (V) divided by current in amps (I).
Equipment
Power pack
Voltmeter
Ammeter
1 metre long wire
Two crocodile clips
Fair test
When carrying out this experiment I will only change one thing, the length of the wire. I 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.
The cross sectional area of the wire must be kept constant throughout as well. 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.
The current that we pass through the wire is to be kept the same, also. If this is changed the temperature of the wire might change in a way that is not constant. I will also turn off the power supply after each reading to keep the wire at the same temperature.
Safety
To maximize safety I kept volts low and when handling the equipment my hands were dry.
Accuracy
To keep my experiment as accurate as possible I need to make sure, that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when we do this. I must also make sure that the wire is straight when we conduct the experiment. If it is not, short circuits may occur and bends in the wire may effect the resistance. The reading that we take of the voltage should be done emediately after the circuit is connected. This is because as soon as a current is put through the wire the temperature of the wire will increase which we do not want to happen as this will affect our results.
Results
Analysis of my results
I found out that my prediction was correct, that the longer the length wire the greater the resistance. I also noticed from my results that the resistance and the length of the wire are proportional. See table below, which shows that they are proportional.
Electricity, the property that transforms electrical energy into heat energy, in opposing electrical current, is resistance. A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure. All metals are conductors.
As a result of the structure of all conductive atoms, the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. Resistance is encountered when the charged particles that make up the current collide with other fixed particles in the material. As the resistance of a material increases so to must the force required driving the same amount of current. As the length of the wire is increased the number of collisions the current carrying charged particles make with fixed particles also increases and therefore the value for the resistance of the wire becomes higher. The material and cross sectional area of the wire is constant throughout the experiment, so the resistance should be directly proportional to the length of wire.