What is Faraday's law?

The induced EMF equals the negative rate of change of magnetic flux linkage: ε = -N dΦ/dt. The negative sign is Lenz's law.

What is magnetic flux?

Φ = BA cos θ. It is the amount of magnetic field passing through a surface, measured in webers (Wb = T·m²).

What does the negative sign mean?

Lenz's law: the induced current creates a magnetic field that opposes the change in flux. If flux is increasing, the induced current produces a field opposing it.

How do I increase the induced EMF?

Increase N (more turns), increase the rate of change of B or A, or make Δt smaller. Doubling N doubles the EMF; halving Δt doubles the EMF.

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NSW · HSCModule 6

Faraday's law induced EMF calculator

ε = -N ΔΦ/Δt. Enter initial and final flux, time interval, and the number of turns.

Inputs

Number of turns NInitial flux Φ₁ (Wb)Final flux Φ₂ (Wb)Time interval Δt (s)

Flux Φ = B × A × cos θ (Wb).

Result

Induced EMF ε

-12.00V

|ε|

12.00V

ΔΦ

0.03000Wb

ε = -N ΔΦ/Δt (Faraday). The negative sign comes from Lenz's law: the induced current opposes the change in flux.

How this calculator works

The calculator takes the change in flux (Φ₂ − Φ₁), multiplies by the number of turns, divides by the time interval, and applies the Lenz sign. Magnitude tells you the size of the induced voltage; the sign tells you the polarity.

Common questions

What is Faraday's law?: The induced EMF equals the negative rate of change of magnetic flux linkage: ε = -N dΦ/dt. The negative sign is Lenz's law.
What is magnetic flux?: Φ = BA cos θ. It is the amount of magnetic field passing through a surface, measured in webers (Wb = T·m²).
What does the negative sign mean?: Lenz's law: the induced current creates a magnetic field that opposes the change in flux. If flux is increasing, the induced current produces a field opposing it.
How do I increase the induced EMF?: Increase N (more turns), increase the rate of change of B or A, or make Δt smaller. Doubling N doubles the EMF; halving Δt doubles the EMF.