Electrons are deflected by a magnetic field because they are charged particles, and moving charged particles experience a force in a magnetic field. This force is known as the Lorentz force.
Understanding the Lorentz Force
The Lorentz force is the force exerted on a charged particle moving in an electromagnetic field. In the context of a magnetic field, the force (F) on an electron (with charge q) moving with a velocity (v) in a magnetic field (B) is given by:
F = q(v x B)
Where:
- F is the force vector (the direction of deflection).
- q is the electric charge of the electron (which is negative).
- v is the velocity vector of the electron.
- B is the magnetic field vector.
- x denotes the cross product.
The cross product (v x B) means the force is perpendicular to both the velocity of the electron and the magnetic field. Because the electron has a negative charge, the direction of the force is opposite to the direction resulting from the cross product.
Why Does This Happen?
Fundamentally, moving charges create magnetic fields. When an electron moves through an existing magnetic field, the interaction between the electron's own magnetic field (created by its motion) and the external magnetic field results in a force that deflects the electron. This is similar to how two magnets interact; they either attract or repel each other depending on the relative orientation of their magnetic fields.
Visualizing the Deflection
Imagine an electron traveling horizontally into a magnetic field pointing vertically upwards. The Lorentz force will be perpendicular to both the electron's velocity and the magnetic field. Applying the right-hand rule (or left-hand rule since the electron is negatively charged), the force on the electron will be in a direction perpendicular to both the velocity and the magnetic field, causing the electron to deflect (e.g., to the left or right).
Implications
This principle is utilized in various technologies, including:
- Cathode Ray Tubes (CRTs): Electrons are deflected by magnetic fields to create images on the screen.
- Mass Spectrometers: Ions (charged particles) are deflected by magnetic fields to determine their mass-to-charge ratio.
- Particle Accelerators: Magnetic fields are used to steer and focus beams of charged particles.
