# Magnetic field

• Magnetic field due to an imaginary magnetic pole (pole strength m) is given by B = F/m0. Also
• Magnetic field due to a bar magnet: At a distance r from the center of magnet
• On axial position,

, If l<<r, then

Fig. 17
• On equatorial position, ;

If l <<r ; then

General position: In general position for a short bar magnet,

# Bar magnet in magnetic field

When a bar magnet is left free in a uniform magnetic field, it aligns itself in the directional field.
• Torque: Ï„ =
• Work:
• Potential energy:  (Î¸ is the angle made by the dipole with the field)

# Gaussâ€™s law in magnetism

Net magnetic flux through any closed surface is always zero, i.e.,