Electricity and Magnetism
In my preliminary experiment I learned that I needed a wire which could withstand the weight of at least 1kg, but also would effectively extend enough to see the significant change. I decided to use the wires with a diameter of 0. 31mm and 0. 27mm. I also decided to use at least 1kg of weights because some parts of the wire may not be all the same so they could be thicker and hold more weight or thinner not take that much weight at all. I think the temperature will be almost the same always, so there is no need to worry about it. I will need to repeat the experiment twice for each wire for greater accuracy.
Specialist Apparatus These are equipment, which make the experiment's results more accurate and in turn the young's modulus. Uncertainties I had uncertainties because, I could not control or keep constant the temperature, so the wire may have extended or contracted. To calculate the strain I had to measure very small extensions of less than 1mm, this was quite difficult, because I did not have specialist equipment to measure length so I had to rely on human decisions, which meant there were always going to be errors. I also had to calculate the stress, therefore I had to use a micrometer to measure the diameter of the wire.
Analysis The table shows that more mass or Newton's means that there will be more extensions to the original length. To get young's modulus I used y = mx+c so I could get an average of it for each ruler. I used the equation: stress over strain to get young's modulus, which was the gradient in the graph. E. g. 4. 11E+03/5. 82E-04=7. 06E+06 To get the other equations, I used theory from secondary data, which is above in the background information.
To get my results I used specialist equipment; such as the micrometer, which is accurate to 0.01 of a millimeter, the uncertainty is 0. 005mm. I also used a metre ruler with mm marking for accuracy, the uncertainty is 0. 5mm. The graphs show that stress is proportional to strain as the points are near the line of best fit, also going through the middle. My graphs show that stress is proportional to strain, also stress is proportional to force and strain is proportional to the extension. As you can see from my prediction I drew a graph of stress against strain and this is correct because as you can see from the real graph it basically follows the same curve.
From my stress-force and strain-extension graphs I do not need to draw error gradients because they are so accurate and because their R2 value is very close to 1. Trend line: A graphic representation of trends in data series, such as a line sloping upwards to represent the average. Trend lines are used for the study of problems of predictions, also called regression analysis. R-squared value: An indicator from 0 to 1 that reveals how closely the estimated values for the trend line correspond to your actual data. A trend line is most reliable when its R-squared value is at 1 or near 1.
It is also known as the coefficient of determination. Evaluation The uncertainty of the extension is 0. 01cm (0. 01/1. 7)*100 = 1. 7% The uncertainty of the length of wire is To ensure I had a safe experiment I wore safety goggles, also setup the experiment in the centre of the table. I made sure that the clamp stand was firmly placed on the floor so that it wouldn't wobble and affect the results taken down.
I tried to keep my eye level in line with the marker measurements to rule out parallax error. I took many results down to have accurate results and averaged them. The reason for the line of best fit not going through the origin there may have been due to systematic error. This may because there was friction on the pulley, to remedy this problem grease could be used. Also the ruler was not long enough for the whole wire to be measured so the 2 rulers may be disjointed, so to remedy this problem I would need a longer ruler.
Also the taught wire may not be horizontal to the pulley when tied to the clamp so the wire is longer than it can be measured, to solve this problem I used a wooden block, but it wasn't enough. The main two measurements that contributed to young's modulus were the diameter and the extensions as they were used to calculate the stress and strain. 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.
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