9702 · 20.3
Force on a moving charge
Imagine tiny charged particles speeding through space, only to be suddenly pushed sideways by an invisible force! This is the **magnetic force** on a moving charge, a fundamental concept in electromagnetism. We'll explore how this force arises, how to predict its direction using **Fleming's Left-Hand Rule**, and its fascinating applications in **velocity selectors** and the **Hall effect**. This pilot aligns with **Senpai Corner** A Level notes (2025–2027) for topic **20.3**.
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
- 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.