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TheWire247
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Homework Statement
In the lectures, we considered a dipole, made of two charges ±q at a separation d. Using
Dirac's δ function, write the charge density for this dipole.
Evaluate the charge (monopole moment), dipole moment, and quadrupole moments Q, p,
and Qij in the multipole expansion for this case and show that p agrees with the dipole moment.
Now consider four charges, all in the xy plane, arranged in a square, centred at the origin
and edges parallel to the coordinate axes, all of magnitude q. Two charges, at opposite ends, are positive, the other two negative.
Find the quadrupole moment for this arrangement. Explain briefly, without calculation, why
the monopole and dipole moments vanish.
Homework Equations
τ=PxE <=electric dipole equation
The Attempt at a Solution
Many of us have been staring at this problem for hours with no success. Any help or pointers in the right direction would be very much appreciated