Force on a moving charge

Need to know

What you need to know

• The force $F = BQv\sin\theta$ is maximum when the charge moves perpendicular to the field ($\theta=90^\circ$).
• The force is zero when the charge moves parallel to the field ($\theta=0^\circ$).
• Fleming's Left-Hand Rule determines the force direction for a *positive* charge. For a negative charge, the force is in the opposite direction.
• The magnetic force is always perpendicular to both the velocity of the charge and the magnetic field.
• Since the force is perpendicular to the direction of motion, the magnetic force does no work on the charge, and its kinetic energy does not change.

Explanation

Force on a moving charge

1. The force $F = BQv\sin\theta$ is maximum when the charge moves perpendicular to the field ($\theta=90^\circ$).
2. The force is zero when the charge moves parallel to the field ($\theta=0^\circ$).
3. Fleming's Left-Hand Rule determines the force direction for a *positive* charge. For a negative charge, the force is in the opposite direction.
4. The magnetic force is always perpendicular to both the velocity of the charge and the magnetic field.