For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat. Aim: To investigate how the resistance of a wire is affected by the length of the wire.
Prediction: The longer the wire, the higher the resistance. This is because the longer the wire, the more times the free electrons will collide with other free electrons, the particles making up the metal, and any impurities in the metal. Therefore, more energy is going to be lost in these collisions (as heat). Furthermore, doubling the length of the wire will result in double the resistance. This is because by doubling the length of the wire one is also doubling the collisions that will occur, thus doubling the amount of energy lost in these collisions. Hypothesis:
I think as you increase the length of the wire, you also increase the amount of resistance. The current is the flow of electrons; the current is dependent on the amount of voltage, which is applied. Voltage is the push given to the current. The current has to go through a circuit, which contains resistance so if you increase that push you also increase the flow of the current. All materials have a slight resistance to electricity factors affecting the resistance are: Length, Voltage & Temperature and Surface Area. Apparatus: 1 x Power Pack (to give varied voltage) 1 x Voltmeter.
1 x Ammeter 2 x wires (with crocodile clips) wire of varied length and thickness Variables: Controlled variables: Temperature (room temperature) Wire material Dependent variable: Resistance Independent variables: Thickness of wire, Length of wire and Circuit diagram. Method: First, set up the experiment as shown above. Turn on the power and set the power pack so that the voltmeter reads 0. 1 volts. Take the reading from the ammeter recording both the current and the voltage. Then do exactly the same again but use voltages of 0. 2 volts, 0. 3 volts, 0. 4 volts and 0. 5 volts.
This is so that when we work out the resistance (V/I) we will have five readings and can then take an average resistance. Then carry out the whole thing again, varying the length of the wire in intervals of 10cm from 10cm to 100cm. To do the thickness experiment, set up the equipment again as shown. Turn on the power and set the power pack to read 0. 2 volts. Take the current reading then turn off the power and start again. Take four readings like this so that an average resistance can be found. Next, change the thickness of the wire and do the experiment again. Use the diameters 0.
71mm, 0. 56mm, 0. 28 mm and 0. 20mm. Although the diameters haven’t the same interval between them, once we have worked out the resistance, we can draw a graph to discover any relationship between the thickness and the resistance of wire. The equation for resistance = V/I Wire 1, Set 1: Length (cm) Voltage (V) Current (A) Resistance (W) Voltage (V) Current (A) Resistance (W) (to 2 d. p. )Having ompleted two sets of results for one wire, it was noticed that these was a large black mark towards one end of the wire, where it appeared that it had been melted to some degree at some point. It was therefore decided to conduct experiments on an additional piece of wire that was checked for integrity prior to investigation:
Wire 2, Set 1: Length (cm) Voltage (V) Current (A) Resistance (W) (to 2 d. p. ) Averages for each wire were then calculated to give these results, which were then graphed: Length (cm) Resistance (W) (to 2 d. p. ) Wire 1 Wire Conclusions Having performed the investigation, the following conclusions were drawn: As predicted, an increase in length resulted in an increased resistance. This can be clearly said for both wires tested. Both wires show a strong trend of a straight line, i.e. the length of the wire is shown to be directly proportional to the resistance – double the length and the resisance doubles.
The overall resistance of the two wires seems to differ considerably. Due to the strong correlation of the results, the explanation of this is unlikely to be the method used to obtain the results. The more likely explanation would be that the first wire was actually of a larger diameter than the second one. Obviously this is a rather important oversight and this will be discussed more in the Evaluation section.
The reason why this is the likely explanation is because resistance is known to be inversely proportional to the cross-sectional area, i. e. if you increase the cross-sectional area (by increasing the diameter) then you decrease the resistance. This is because a wider wire means less likelihood of the free electrons having collisions and losing energy. It is important to realise, however, that despite the fact that it would appear that the resistance of wire 2 is double that of wire 1, that does not mean that the diameter is half that of the wire 1.
That is because if you halve the diameter then you decrease the area by a factor of about 3 (A = ? r2) Evaluation the biggest downfall of the investigation was the apparent mistakes when choosing the wire, in that they would appear to be of differing diameters. This did not, in this case, cause a big problem as the same wire was used for each set of results so it is known that the results for each wire are correct. Generally speaking, wire 1 would appear to contain the most accurate results due to the fact that all of its points bar one sit on the line of best fit for that wire.
The only one that does not is the point at 90cm, which was exactly at the point that the black mark (mentioned previously) was found to be. Wire 2, on the other hand, had three main anomalous results: at 50, 80 and 90cm. They are by no means that far off but in an experiment such as this, which is generally a very accurate one anyway, such anomalous results should not be quite so common. Possible explanations for these anomalies are as follows: o The length of wire for that particular measurement was not correct.
At 50 and 80cm it is possible that the length was shorter, causing a lower resistance, and at 90cm it is possible that it was longer, causing a higher resistance. The solution to this is to measure the lengths more carefully and ensure that the wire is pulled tight against the metre rule. o For a particular result, one or more of the connections could have been faulty, causing extra resistance at the connections. A solution to this would be to, before each experiment, connect the connections together without the wire in place and measure the resistance then.
If it is higher than it should be then the connections could be cleaned. o Whilst extremely unlikely, it is conceivable that the power supply was providing a different voltage for some of the results. This is unlikely to be a problem in this investigation but it might have been an issue had we used batteries instead. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.