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Old Mar 14th 2014, 06:38 AM   #1
ems
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Which factors change electrostatic force?

I have measured the electrostatic force between an earthed plate and charged sphere, then varied the separation between them.

I plotted a graph of this variation with separation (attached). The dashed line shows where the points should lie. Does anyone have any suggestions as to why my graph is too steep? What factors could make this relationship arise?

Any help would be greatly appreciated!!
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Which factors change electrostatic force?-graph.jpg  
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Old Mar 15th 2014, 05:09 AM   #2
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Just to check something: the vertical axis is N^1/2, so your force measurements were all around 230N or so, correct? That seems like a lot - how did you measure the force?
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Old Mar 15th 2014, 10:13 AM   #3
ems
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Originally Posted by ChipB View Post
Just to check something: the vertical axis is N^1/2, so your force measurements were all around 230N or so, correct? That seems like a lot - how did you measure the force?
The force measurements were all of the order 10^-3 - i.e. 0.002N, etc. The force was measured using a digital force meter
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Old Mar 17th 2014, 06:22 AM   #4
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What formula did you used to calculate the dashed line? The force is not going to be something as simple as 1/R^2, due to the geometry of the set up. Something else that strikes me as well: you say the plate is "earthed" - in which case it has no charge on it, so the electrostatic force between it and the sphere should be zero! Am I missing something here? But be that as it may, I have a few more questions:

1. On the horizontal axis what does "2s+d_0" mean?
2. What is the accuracy of the force gauge? Can it distinguish between, say, 0.0020N and 0.0021N?
3. You have what look like error bars on the distance measurements but not the force measurements - why is that, and how did you determine their magnitude?
4. What is the radius of the sphere, and the width of the plate?

Last edited by ChipB; Mar 17th 2014 at 11:45 AM.
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