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To see how the length of a wire affects its resistance. To find the wire to test, I’m going to test 4 different types of wire in another experiment and use the one with the highest resistance. The Theory behind the Experiment Theoretically the length of a wire should affect its resistance. Electricity encounters a certain amount of obstruction when passing through a wire depending on its length, width, temperature and type of metal, this obstruction is called the resistance and is measured in ohms.

The longer and thinner the wire the harder it is for the electrons to flow through, because there are less spaces for it to flow through and more obstructions along the length. It has a similar principal to the flow of water and how it is impeded when passing through a long and narrow pipe. Therefore the longer the wire is the more resistance there should be.

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The other factor that can affect the resistance is the metal type, for example the resistance of an Iron wire is about seven times greater than that of a copper wire with the same dimensions, and this is because of the varied amount of ions in the different metal, more ions in Iron mean that electrons find it harder to pass through. This is the reason why copper is used in electrical wire; because it gives little resistance less energy is used to make it flow. I need to test 4 different wires in the first experiment; to find the type of wire with most resistance.

It is important that for both experiments I let the wire cool down for a few seconds after taking the reading, as temperature can affect the resistance. This is because the molecules in the wire when heated vibrate more and the electrons find it harder to pass through, thus the resistance will increase. When connecting the circuits for both experiments I need to make sure the voltmeter is in parallel with the wire and the ammeter is in series. This is shown in a diagram of apparatus later on. George Simon Ohm (1789-1854) was one of the first people to investigate current and voltage and came up with the following law for metallic conductors.

The current through a conductor is proportional to the potential difference between its ends, provided that physical conditions, such as temperature, remain constant: i. e. V/I = constant (resistance). Where v = voltage and I = current. This means regardless of the size of the current, as long as there is no temperature change the resistance of a wire remains constant. The law is based on experiment (empirical) and holds remarkable accuracy for metallic conductors which are what I’m going to use in my experiment.

It is important to note that the circuits I will be using for my experiments are in series because in parallel and series circuits the methods for calculating the total resistance for more than one component are different. In series the resistance across the components are added together: R = R1+R2. Whereas in Parallel the current divides, the larger part going through the smaller resistance and the smaller part through the larger resistance: 1/R=1/R1 + 1/R2. So the resistance is smaller because it is like a single wire with a large cross section and therefore more spaces in the atoms for the electrons to pass through.

I’m going to prove that resistance is proportional to length. The greater the cross sectional area of the conductor the more electrons available to carry the charge along the conductor’s length and so the lower the resistance is. Resistance is inversely proportional to cross sectional area. Key Variables: Key Variables Explanation Temperature of wire If the wire is hotter the atoms will be vibrating more, making it harder for the electrons to pass through and increase the resistance. Thickness of wire The fatter the wire the easier it is for the electrons to flow through as there are more spaces between the atoms or molecules.

Length of wire The longer the wire the more difficult it is for electrons to flow through and producing a higher resistance Type of wire In different conductors the ease of flow of electrons is different and so conductors have different resistances. Wires connected to the battery pack Different wires can produce slightly different resistances and therefore they must me kept the same throughout both experiments. Experiment Independent Variable Controlled Variables Dependant variable 1 Type Of Wire: Constantan, copper, Nichrome and Manganin Length, Thickness, Temp, Voltage, Wires connected to battery pack.

We will find the voltage and current and use this information to find the wire with most resistance out of the four. 2 Length Of Wire Type of wire, temp, thickness, voltage, wires connected to battery pack. We will find the voltage and current but his time workout the resistance and see if there is a relationship between the length and resistance. Outline Plan 1st experiment We have four different types of wire attached to two metre rules they are: Manganin, Nichrome, Copper and Constantan.  We will measure the current and voltage for each wire separately, one after the other.

To make it a fair test we will make sure there are no changes in the temperature, thickness, or length that would affect our experiment for reasons explained earlier in “The theory behind the experiment”. The voltage will also be kept at 2v for each test to prevent over heating of the wires and subsequent inaccurate results.  To measure the independent variable accurately we’re going use specific apparatus: a metre rule with the different wires attached either end (to measure the voltage and current we’re using a standard ammeter and voltmeter).

We will also be carrying out the test for each wire 3 times, which will make our results more reliable and accurate when making an average. The wood will not conduct electricity to avoid interference in the results, making it a suitable material to base the wire on.  The reason we will be using the wire with the most resistance is because it less likely to overheat because it will not let the electrons through as quickly. If the wire overheats, not only will it affect the results of the experiment (ohms law only works at a constant temperature), it would also be a safety hazard as touching it could burn you.

For both experiments we will be using crocodile clips, for the first experiment this is because they can be attached to the wire easily, safely and without the risk of them falling off. 2nd experiment  We’re going to take the wire with the most resistance from the first experiment a measure its current and voltage at different lengths. We will do this by recording the amps and volts using an ammeter and voltmeter at 10cm intervals for 100cm (10 recordings). This is why we use the metre rule, because it has the measurements on it already.

After recording every result I will let the wire cool before taking the next reading at the next interval by switching the battery pack off for approximately 30 seconds, this is to prevent a raise temperature from affecting our experiment making it an unfair test. We will measure the dependent variable more accurately with more reliable results by repeating the test 3 times and making an average for each length using the 3 results.  The specific apparatus I’m going to use is a metre rule with the wire attached for the same reasons as in the 1st experiment.