- #1
mateomy
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Imagine a cube with side lengths 'r', (like a dice) and we put point charges of charge Q at each corner of the cube.
Issues with 2 subsections of this problem...
First: What is the total electrostatic potential energy of the arrangement?
Second: Add a charge -CQ to the center of the cube for what value of C will the total potential energy be negative?For the first part I've calculated the potential energy of the system to be
[tex]
\frac{Q^2}{4\pi\epsilon}[\frac{12}{r} + \frac{13}{r\sqrt{2}} + \frac{4}{r\sqrt{3}}]
[/tex]
Does that seem correct? It was a pretty lengthy algebraic adventure but I feel like it works out, its just a summation of the radii between charges (non-repeating of course).
For the second part I'm pretty lost:
I've calculated the total potential at the center to be
[tex]
\frac{4Q}{\sqrt{3} \pi \epsilon r}
[/tex]
Now, I don't know how to determine the max value of C to see when the whole potential would be thrown into the negative. Do I add the two expressions together and solve for C? I'm pretty lost. I even recalculated the potential from the first part but threw in the charge with the other eight Q's to no avail.
[tex]
\frac{Q^2}{4 \pi \epsilon}[\frac{12}{r} + \frac{13}{r \sqrt{2}} + \frac{4}{r \sqrt{3}} - \frac{14C}{r \sqrt{3}}]
[/tex]
The roots are giving me trouble to simplify things to a discrete integer. Any pointers would be appreciated.
Thanks.
Issues with 2 subsections of this problem...
First: What is the total electrostatic potential energy of the arrangement?
Second: Add a charge -CQ to the center of the cube for what value of C will the total potential energy be negative?For the first part I've calculated the potential energy of the system to be
[tex]
\frac{Q^2}{4\pi\epsilon}[\frac{12}{r} + \frac{13}{r\sqrt{2}} + \frac{4}{r\sqrt{3}}]
[/tex]
Does that seem correct? It was a pretty lengthy algebraic adventure but I feel like it works out, its just a summation of the radii between charges (non-repeating of course).
For the second part I'm pretty lost:
I've calculated the total potential at the center to be
[tex]
\frac{4Q}{\sqrt{3} \pi \epsilon r}
[/tex]
Now, I don't know how to determine the max value of C to see when the whole potential would be thrown into the negative. Do I add the two expressions together and solve for C? I'm pretty lost. I even recalculated the potential from the first part but threw in the charge with the other eight Q's to no avail.
[tex]
\frac{Q^2}{4 \pi \epsilon}[\frac{12}{r} + \frac{13}{r \sqrt{2}} + \frac{4}{r \sqrt{3}} - \frac{14C}{r \sqrt{3}}]
[/tex]
The roots are giving me trouble to simplify things to a discrete integer. Any pointers would be appreciated.
Thanks.