Wednesday, March 18, 2015
Monday, January 19, 2015
I have modified the example of electrofied oil (ex 15.4) to show what happens when the charge on the oil drop changes. The electric force (Fe) on a negative charged oil drop will be upward while the gravitational force (Fg) is downward. If Fg is greater than Fe the drop will have negative acceleration and will fall. If there is enough charge on the particle so that the electric force exceeds the gravitational force the particle will have positive acceleration and will rise. For the example below I started with a charge of 3 electron on the oil drop and there is essentially no acceleration. With two electron charges there will be less electric force and the particle accelerates slowly downward. With 1 electron charge the drop has even larger negative acceleration. If the drop contains no charge at all it will fall at the acceleration of gravity (as it should in a vacuum). So the conclusion is that the drop will have the greatest negative acceleration (but not as much as g) when the charge on it is the least it can be. The least it can be is 1.6x10^-19 C. Try working this problem when the drop contains 4 electron charges, i.e., 4 x 1.6x10^-19 C.
Wednesday, January 14, 2015
The following may be helpful for getting started with the homework problems for chapter 15. I don't know how the "Blog" feature will eventually work or even if it will be useful but I would like to make it possible for anyone in the class to submit comments or questions and I can give answers as needed. Hopefully, there will be a running dialog which will benefit everyone. Please do not hesitate to offer suggestions for anything else I can do to help. If someone cares to post a comment or question we can see how things might work.
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| The above is actually problem 15.15 |
Sunday, January 11, 2015
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