2 Dipole in a Uniform Magnetic Field The Electrostatic Analogue

Dipole in a Uniform Magnetic Field The Electrostatic Analogue

Force on N-pole = mB, along

Force on S-pole = mB, opposite to 

Where,

m → Strength of each pole

B → Strength of magnetic field

These equal and unlike forces form a couple, which tends to rotate the magnet clockwise so as to align it along.

Torque acting on the bar magnet,

τ = Force × Perpendicular distance

= mB × NA

In ΔNAS,

∴ NA = 2l sin θ

Now,

τ = mB × 2l sin θ

⇒ τ = B × (m2l) sin θ

τ = MB sin θ

The Electrostatic Analogue

• The magnetic dipole moment of a bar magnet is given by

Where,

m → Strength of each pole

2l → Length of the dipole

The magnetic dipole is analogous to an electric dipole consisting of two equal charges of opposite sign (± q) separated by a certain distance . It has an electric dipole moment,

• The equations for magnetic field () due to a magnetic dipole can be obtained from the equations of electric field due to an electric dipole by making the following changes:

Thus, for any point on axial line of bar magnet at a distance (d) from the centre of magnet,

Similarly, equatorial field () of a bar magnet at a distance d, for d >> l,