Question

A short bar magnet placed with its axis at 30° with an
external field of 800 G experiences a torque of 0.016 Nm. (a) What is
the magnetic moment of the magnet? (b) What is the work done in
moving it from its most stable to most unstable position? (c) The bar
magnet is replaced by a solenoid of cross-sectional area 2 × 10–4 m2
and 1000 turns, but of the same magnetic moment. Determine the
current flowing through the solenoid.

Answer 1

θ=30

o

B=0016 T

z=0.032

z=mBsinθ

0.032=m×

2

1

×0.16

m=0.4 Am

U=−

m

.

B

U

max

=mB=0.4×0.16=0.064 T

U

min

=−mB=−0.4×0.16=−0.064 T