A small current-carrying loop is located at a distance r
from a long straight conductor with current I. The magnetic moment
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of the loop is equal to pm. Find the magnitude and direction of the
force vector applied to the loop if the vector pm
(a) is parallel to the straight conductor;
(b) is oriented along the radius vector r;
(c) coincides in direction with the magnetic field produced by the
current I at the point where the loop is located.