Moving charged particles in a magnetic field
  • Recall the motor effect. If a current passes through a magnetic field it experiences a force.
  • As a current is just charge over time ($I = \frac{q}{t}$), a charge moving in a magnetic field would also experience a force.
  • This force's direction can be found by the Right-Hand rule.
  • As such, only the perpendicular component of the partice's motion is taken into account.
  • Thus, mathematically, this force can be defined as:
\begin{align} F = qvB\sin{\theta} \end{align}


  • $F$ is the force on the particle. (N)
  • $q$ is the charge on the particle (C)
  • $v$ is the velocity that the proton is travelling ($ms^{-1}$)
  • $B$ is the magnetic field strength (T)
  • $\theta$ is the angle between the direction of the charged particle and the magnetic field.