Aim: To investigate how the electrical resistance of a wire changes in relationship to it’s length. The experiment will be carried out using a current flowing through different lengths of wire, to see what effects are made in relation to the resistance. Introduction: I am going to carry out an experiment with a wire, to test the resistance of it. I am going to do this in order to get a wider knowledge of how electricity works. Also I wish to learn more about the resistance of wires in relation to their lengths. As the electricity flows through the wire, it encounters obstacles in the molecules that make up the wire.
Every time the electricity encounters a new obstacle, the resistance increases slightly. I will use a wide range of lengths in order to get the greater variation in results. I will repeat the experiments several times in the name of a fair test. Prediction: I presume that as the length of the pieces of wire are change, the resistance will increase or decrease to the same pattern. this leads me on to presume that the rate of increase / decrease of the wire length, will directly lead to a proportionally accurate change in the resistance. this would make the graph appear somewhere along the lines of this: Y X.
Reason: With 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 can be used as conductors. some are better than others, but they all look something like this: 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. When charged particles (current) encounter fixed particles (metal) they cause a collision. these collisions are known as resistance. When the resistance of a current is increased, this must require the force behind the current to increase. This makes resistance (ohms) is the same as the potential difference (volts) divided by the current (amps). this is called Ohms law. R=V / I As the length of the wire increases, it stands to reason that the resistance increases because there are more particles to collide with and therefore the value for the resistance of the wire becomes higher.
Resistance, in ohms (R) is also equal to the resistance of the wire, in ohm-meters (N) multiplied by the length, in meters (l) divided by the cross sectional area, in square meters (A). R=(N *I) / A The material and cross sectional area of the wire is constant throughout the experiment. Therefore it is clear from the formula that the resistance should be directly proportional to the length. Key factors: In this experiment we will only change one factor, the length of the wire. This should effect the resistance of the wire in the ways stated above.
Fair test: This experiment requires us to change only two factors, the length of wire, and the thickness of it. These are the factors that we will keep the same: – 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. – The cross sectional area of the wire must be kept constant throughout as well. This is shown in equation (2) where the cross sectional area is a factor that effects the resistance. – The material of the wire must also be kept the same as different materials have different conductivity.
The last two constant factors mentioned can be kept constant by using the same pieces of wire, through out the entire experiment. The current that we will allow to pass through the circuit will be kept constant as well. If the current is changed, the temperature will increase, as well as the force behind the current. this will lead to very odd results. Apparatus: 1. Wire, 100 cm long 2. Power supply 3. Six connecting wires 4. Two crocodile clips 5. Voltmeter 6. Ammeter Plan: 1. Connect the circuit so that it looks like the one shown above 2. Make sure that the current is set at 3 amps 3.