Question

A bar-magnet with magnetic moment 2.5 Am^2 is placed in a homogeneous magnetic field (of 0.1 T that is directed along the z-axis). What force and torque will the bar-magnet experience due to the magnetic field if: a) The north-pole of the magnet is pointing along the z-axis?
b) The north-pole of the magnet is pointing 45° relative to the z-axis?
c) The north-pole of the magnet is pointing 90° relative to the z-axis?

Answer 1

Answer:

1)

Force on bar magnet  = 0

Torque on bar magnet = 0

2)

Force on bar magnet  = 0

Torque on bar magnet = 0.177 Nm

3)

Force on bar magnet  = 0

Torque on bar magnet = 0.25 Nm

Explanation:

Part 1)

net force on bar magnet in uniform magnetic field is always zero

Torque on bar magnet is given as

$\tau = MBsin\theta$

when bar magnet is inclined along z axis along magnetic field

then we will have

$\tau = MBsin0 = 0$

Part 2)

net force on bar magnet in uniform magnetic field is always zero

Torque on bar magnet is given as

$\tau = MBsin\theta$

when bar magnet is pointing 45 degree with z axis then we will have

$\tau = MBsin45$

$\tau = (2.5)(0.1)sin45$

$\tau = 0.177 Nm$

Part 3)

net force on bar magnet in uniform magnetic field is always zero

Torque on bar magnet is given as

$\tau = MBsin\theta$

when bar magnet is pointing 90 degree with z axis then we will have

$\tau = MBsin90$

$\tau = (2.5)(0.1)sin90$

$\tau = 0.25 Nm$