Preliminary Results For this experiment I needed to decide what material to use. I decided to test the materials three times on the same carbon track and find the average results. Here is a table to illustrate my results. The length of the carbon track was kept constant at 6cm as too the width was kept constant at 1cm Material .
Using these results I have decided to use the copper hoops. This is because these are the most accurate because they cover up lots of the carbon track. The pins are so thin that they connect to parts of the carbon track where there is no carbon and parts where they connect to just carbon. This varies the results greatly and so this is why I shall not use these. The most commonly used would be the copper with the large surface are because it covers the carbon track more than any of the other materials. So, I shall investigate the resistance in the change of length and width of a carbon track with copper hoops.
I shall compare these results with the copper with the large surface area. Method: Apparatus: Ohmmeter B pencil Graph card Copper (hoop and large surface area) 2 leads 2 Crocodile clips Scalpel Ruler To start this experiment I will set up the apparatus as shown in the diagram. If I were to take the resistance of length, I will start with 1cm going up to 21cm in odd numbers. I will part the copper (hoops) by the measurement that I want to use, on the carbon track, by using the grid on the graph paper as each square is 1cm3.
I will note the result on the ohmmeter, making sure I’m not touching the crocodile clips or copper hoops. I will then move the copper hoops on a different part of the track, keeping the same measurement, and note it again. Then I will move it to a different part of the track, still keeping the same measurement, and note the result. Using these three results for the same measurement I will find the average of them and then this will be my final result for that measurement. I will do this for each measurement.
For the width I will make a carbon filled square of 12 by 12, but only taking measurements of 1-10. I shall do the same method as taking the length results (moving the copper hoops at different points of the line, three times for each measurement, and then finding the average). The results are noted down and put into tables and graphs. Precautions and special techniques To obtain different lengths of carbon track I will make the carbon track a lot larger than my largest reading that I am to take, so that I can take three readings of a certain length to investigate in different parts of the track.
To make sure the carbon is a uniformly thick as possible I will take a long time in pressing down the carbon on the pencil until I can see that there are no white spaces and that it becomes very dark and slightly shiny. To obtain different widths of carbon, I will make a square box, on the paper, of carbon and cut off 1cm after each result. The pencil I will use will be a B pencil so that it gives off more carbon more easily. I will make sure that the lines are parallel by placing my ruler on the edge of the line to be made, and keep that as a guide line so that the carbon track does not over run the line.
I will use a digital microscope to look more closely at the carbon track to see how uniform it is. Safety This is quite a safe experiment to undertake, but as this experiment is taken in a laboratory, the usual laboratory rules must still be considered and followed. Any careless mistakes in this experiment could have serious consequences. Carbon is dangerous if inhaled as it would cause irritation of the respiratory tract. Mild irritation and redness on contact with skin and most seriously chronic exposure is known to cause disease and cancer of the lungs.
Although a fairly large amount of carbon is needed to do this, you must be sensible whilst handling carbon and to still wash it off quickly if it gets on your skin. Results Results 1 Length (cm) Width (cm) Te The reciprocal of width against resistance Conclusion Results 1 Length The length graphs for results 1 and 2 (graph 1 and 4) were very accurate and very close to what I would have expected to look like, but when the best fit lines were added, they did not pass through zero, suggesting that there may have been some degree of experimental error in this experiment.