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# Mock AS Physics Coursework, Error bars? watch

1. Ok, so basically, I'm doing my mock analysis section later in the week, and we've been told that we need to do error bars for either the stress or strain (Young Modulus experiment), but not both, and that we need to choose the one that generates the most error.
So, if i used a metre stick to measure length and extension, and a micrometer screw gauge to measure diameter, and a top-pan balance to measure the mass of the load, which would be likely to generate the largest percentage uncertainty, stress or strain?
Or should I just work it out when I get to the lesson on Friday? And see which causes the greatest uncertainty by using maximum force and minimum area, and then the converse to find the uncertainty in stress, and then the maximum extension and minimum length, and then the converse to find the uncertainty in strain, and then compare the percentages? Does this method make sense?

2. In all your calculations you take all readings (all have errors) and then substitute them into your formula.

To find the max limit all multipliction terms must be maximised and all division terms must be minimised. This gives you your upper error.

Do the reverse for the minimum error.

The key is you need to find out the errors possible for each type of measuring instrument.
3. (Original post by TeslaCoil)
Ok, so basically, I'm doing my mock analysis section later in the week, and we've been told that we need to do error bars for either the stress or strain (Young Modulus experiment), but not both, and that we need to choose the one that generates the most error.
So, if i used a metre stick to measure length and extension, and a micrometer screw gauge to measure diameter, and a top-pan balance to measure the mass of the load, which would be likely to generate the largest percentage uncertainty, stress or strain?
Or should I just work it out when I get to the lesson on Friday? And see which causes the greatest uncertainty by using maximum force and minimum area, and then the converse to find the uncertainty in stress, and then the maximum extension and minimum length, and then the converse to find the uncertainty in strain, and then compare the percentages? Does this method make sense?

This is for a metal wire, I assume.
You need to have an awareness of where the greatest %age uncertainty lies in individual measurements.

Think:
What sort of value do you expect for the extension of the wire?
If you are measuring this extension with a metre rule, what is the % uncertainty in that? (A meter rule has a scale marked in mm.)
You should find it to be rather large. Certainly larger than the other uncertainties.
I suggest you measure the extension with some sort of vernier scale.

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Updated: March 14, 2013
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