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PY212 Solutions Quiz 6
(a) The torque is given by
B
r
r
r
×
=
μ
τ
and therefore the magnitude of the torque is equal to
θ
sin
B
=
. Here
θ
is the angle between
B
r
and the dipole moment
r
(which is a vector
perpendicular to the plane of the loop; see Fig. 28-24). If the torque on the coil is
maximized, we must have
sin
θ
= 1, i.e.
θ
= 90
°
.
(b) If
N
closed loops are formed from the wire of length
L
, the circumference of each
loop is
L
/
N
, the radius of each loop is
R = L
/2
π
N
, and the area of each loop is

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