The relation between the D and
E fields and between the
B and
H fields. These relations depend on the material properties.
Two equal and opposite charges +q and
−q separated a short distance
d. The electric dipole moment is given by
p =
qd, where
d is a vector going from
−q to +
q.
A small circular loop carrying a current. The magnetic dipole moment is m =
IAe, where
I is the current carried by the loop,
A its area, and
e a unit vector along the central axis of the loop.