When a charged particle moves parallel to a magnetic field, what is the magnetic force on it?

When a charged particle moves parallel to a magnetic field, what is the magnetic force on it?

• A. The force is maximum
• B. The force is zero
• C. The force equals qvB
• D. The force is independent of velocity

Answer: (B)

When a charged particle moves in a magnetic field, it experiences a magnetic force given by F = q v × B. The magnitude of this force is F = q v B sin θ, where θ is the angle between the velocity and the magnetic field. If the particle moves parallel to the field, θ = 0, so sin θ = 0 and the magnetic force is zero. With no magnetic push, the particle continues in a straight line along its original velocity, at constant speed (the magnetic field does no work on it). The force would be largest if the velocity were perpendicular to the field, giving F = q v B, and it depends on both speed and orientation, not on speed alone.

When a charged particle moves in a magnetic field, it experiences a magnetic force given by F = q v × B. The magnitude of this force is F = q v B sin θ, where θ is the angle between the velocity and the magnetic field. If the particle moves parallel to the field, θ = 0, so sin θ = 0 and the magnetic force is zero. With no magnetic push, the particle continues in a straight line along its original velocity, at constant speed (the magnetic field does no work on it). The force would be largest if the velocity were perpendicular to the field, giving F = q v B, and it depends on both speed and orientation, not on speed alone.