5. Once you establish the forces, you have a PHYS 207 problem. What kind of PHYS207 problem?
6. Notice that
and that the right-hand form of this quantity is much easier to calculate for squares, cubes, etc.
7. The definition of the electric dipole moment vector for a set of charges qi at positions ri is
P = sumi [ qi ri ]
(a+b)n = a2 + (n/1!) an-1 b + [n(n-1)/2!] an-2 b2 + ...
9. You can use the derivation of the field due to a dipole which we did in class as a source of ideas for this one. Even though the angles and the quantities calculated are different, the situation is similar and the geometry related.
10. To get the electric field for several charges, you must sum over the contributions of all the individual charges. How do you accomplish the same objective when the charge is a continuous function of position?
The last part can be done without an explicit calculation.
11. This problem requires thought, not reams of algebra, and the answer is very simple. PHI is a measure of the number of electric field lines passing through a surface, physical or purely mathematically. Draw a good diagram and study the electric field lines. The answer is
What determines the sign?
| Last revised 1998/02/20 |