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Lorentz Force

A wire fashioned into a pendulum moves inside a magnetic field, demonstrating the Lorentz force.

A charged particle moving through an applied magnetic field experiences a force that is at right angles to both the direction in which the particle is moving and the direction of the applied field.

This force, known as the Lorentz force, develops due to the interaction of the applied magnetic field and the magnetic field generated by the particle in motion.

The phenomenon is named for Dutch physicist Hendrik Lorentz, who developed an equation that mathematically relates the force to the velocity and charge of the particle and the strength of the applied magnetic field.

Instructions

  1. Take a look at the setup. A battery is connected in a circuit with a wire shaped like a pendulum. A permanent horseshoe magnet is looped around the pendulum.
  2. Click on the close switch button to close the knife switch and complete the circuit. The black arrows show the direction the current is flowing.
  3. Note how the pendulum swings toward the battery, because of the interaction of the magnetic field traveling through the wire and the magnetic field from the horseshoe magnet.
  4. Click "show wire field lines" or "show magnet field lines" to reveal the interplay of the magnetic fields that are creating the Lorentz Force on the pendulum.
  5. Try hitting the button to flip the battery. Notice how when the current is flowing in the opposite direction, this affects the magnetic fields and pushes the pendulum the opposite direction.
  6. Now push the "flip magnet" button to see how changing the poles of the magnet affects the pendulum as well.

You can predict which way the wire will move by using the left-hand rule.

If your index finger points in the direction of a magnetic field, and your middle finger, at a 90 degree angle to your index, points in the direction of electrical current, then your extended thumb (forming an L with your index) points in the direction of the Lorentz force exerted upon that particle, and the direction in which the wire shifts in the tutorial.