Lenz's Law Calculator

Lenz's Law states that the direction of an induced current always opposes the change in magnetic flux that caused it. It is embedded in Faraday's Law through the negative sign: ε = −N × (ΔΦ/Δt). While Faraday's Law gives the magnitude of the induced EMF, Lenz's Law tells you the direction — the induced current creates a magnetic field that resists the change in flux. See also our Cyclotron Frequency Calculator.

The negative sign represents Lenz's Law and is a consequence of the conservation of energy. If the induced EMF aided the change in flux rather than opposing it, the system would continuously amplify itself without energy input — violating the law of energy conservation. The minus sign ensures the induced EMF always acts to resist the cause.

Magnetic flux is measured in Webers (Wb) in the SI system. One Weber equals one Volt·second (V·s) or one Tesla·meter² (T·m²). This calculator supports multiple units including milliwebers (mWb) and microwebers (μWb) for convenience with small-scale measurements.

Eddy current brakes work by moving a conductive disc through a magnetic field, inducing eddy currents that oppose the motion (Lenz's Law). This creates a braking force proportional to the speed, making the braking smooth and consistent. Unlike friction brakes, they require no physical contact and produce no wear. You might also find our Hall Coefficient Calculator useful.

Motional EMF arises when a conductor moves through a magnetic field. It is calculated as ε = B × L × v, where B is the magnetic field, L is the conductor length, and v is the velocity. Use this mode when you have a moving conductor in a uniform field rather than a stationary coil experiencing a changing flux.

In regenerative braking, the electric motor acts as a generator. When the vehicle decelerates, the motor's rotation induces a current (opposing the motion per Lenz's Law), which charges the battery instead of being wasted as heat. The theoretical maximum energy recovery is limited by system efficiency, resistance losses, and battery charge rates.

When a magnet is brought near a superconductor, Lenz's Law induces currents that generate a perfectly opposing magnetic field (the Meissner effect). Because the superconductor has zero resistance, these currents never decay, maintaining a persistent repulsive force that levitates the magnet indefinitely.

Induced EMF (ε) is the electromotive force generated by the changing flux — it's a voltage-like quantity measured in Volts. Induced current (I) is the actual electric current that flows when the EMF drives charge through the coil's resistance, calculated as I = ε / R. Provide the coil resistance to compute the induced current.