The Lorentz force
The single equation underneath every electric motor.
- Explain the lorentz force at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
Every torque an electric motor produces traces back to one simple relationship: a current-carrying conductor in a magnetic field feels a force.
In depth
Force on a straight conductor equals flux density times current times the conductor's length within the field.
Magnetic field explorer
Adjust current, turns and air gap and watch flux density and force respond in real time.
Flux is proportional to volts per hertz. Hold that ratio constant and torque stays constant as speed rises — which is exactly what a variable-frequency drive does below base speed.
Direction matters
The direction of the force is given by the right-hand rule: point your fingers along the current, curl them toward the field, and your thumb points along the force. In a motor, this force acts tangentially on the rotor surface, which multiplied by radius gives torque.
Key takeaways
- F = B × I × L is the fundamental force law behind all motor torque.
- The right-hand rule gives the direction of force from current and field.
- Torque is that force multiplied by the radius at which it acts.
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