Educator

Magnetic Field

• A compass needle may be used to map the magnetic field lines.
• An electric field exerts a force on a charge, whether the charge is stationary or moving. A magnetic field, however, exerts a force on a charge only if it is moving. The force is given by F = q v x B; it is the charge q times the cross product of the velocity v and magnetic field vectors.
• Since the magnetic force is always perpendicular to the velocity, a magnetic does no work on a moving charge, and thus it does not change its speed.
• If a charge, in a region where a uniform magnetic field exists, is given an initial velocity perpendicular to the field, then it will move in a circle.