The investigation involved testing the factors of pencil lead length, cross-sectional area, temperature and lead type to find out how they affected pencil resistance. The hypothesis was proven as the length (series circuit) graph was exponential and the area (parallel circuit) graph was that of a power function. Higher clay based pencils (2H) had higher resistance to that of higher graphite based pencils (6B), and temperature did not greatly affect the resistance. The reasons as to why diamond does not conduct electricity were also found.
To investigate the effect that different factors have on pencil lead (graphite) resistance. The factors tested include, pencil lead type (HB, 2B...), temperature, length and cross-sectional area. Hypothesis:
The relationship between length and resistance should show an exponential relationship. The relationship between cross sectional area and resistance should be a power relationship. The type of lead and resistance will not show any linear relationship, but it is assumed that the more clay based leads 2h will have higher resistance than the more graphite based 6B. The temperature results will also be difficult to graph effectively due to very little change in the current and voltage. Justification of Hypothesis:
As learnt in class, via earlier experiments, the longer the length of a resistor the lower the current as electrons have further to travel which intern gives a higher resistance. This has been proven by series circuits which is the method in which length will be tested. Area will be tested by using parallel circuits, doing so the cross-sectional area of the resistors is increased while the distance is kept the same. This allows the electrons to pass more freely increasing the current and reducing the resistance. The resistance of pencils of different lead types will be difficult to analyse as the grading of pencils does not incur the resistance, furthermore access to all types of pencil leads may be difficult therefore not allowing testing on each type of pencil lead and leaving gaps and jumps in the data. For the testing of temperature shorter, thicker pencils would increase the rate at which pencil leads heat up, this mean that a 5cm 6B lead pencil should heat up much faster than a 15cm 2h pencil but due to not much change happening in the heating up of a pencil resistance should only change fractionally.
In all of the tests pencil lengths were 17.5cm long. In the testing of length and cross sectional area, HB pencils were used, in the testing of temperature a 2B pencil was used and in the testing of type of pencil lead a 2H, HB, 2B, 4B and 6B pencils were used. Before any tests are begun make sure both ends of the pencils have been sharpened. Test for length (series circuits):
1. Attach the power pack to the power point and set the voltage to 6v. 2. Connect the amp meter to the positive terminal of the power pack. 3. Connect one end of the HB pencil to the negative end of the amp meter and the other end to the negative terminal of the power pack. 4. Turn on the power pack and record the results from the amp meter. 5. Turn off the power pack; add another pencil into the circuit between the first pencil and the negative terminal of the power pack. 6. Repeat steps 4 and 5 until all four pencils have been put into the circuit and recorded. Test for cross-sectional area (parallel circuits):
1. Attach the power pack to the power point and set the voltage to 6v. 2. Connect the amp meter to the positive terminal of the power pack. 3. Connect one end of the HB pencil to the negative end of the amp meter and the other end to the negative terminal of the power pack. 4. Turn on the power pack and record the results from the amp meter. 5. Turn off the power pack; connect the next pencil to the ends of the other pencil. 6. Repeat steps 4 and 5 until all...