Faraday Law Calculator

Faraday law states that changing magnetic flux through a coil induces an EMF. The faster the flux changes or the more turns, the greater the voltage. This is the principle of all electric generators.

⚡ Electromagnetism📐 EMF = N|ΔΦ/Δt|🧲 Induction

Number of Turns N

Flux Change ΔΦ (Wb)

Time Interval Δt (s)

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Induced EMF	EMF	EMF = N\|ΔΦ/Δt\|	V
Magnetic Flux	Φ	Φ = BA cosθ	Wb
Turns	N	Number of coil turns	—
Flux Change	ΔΦ	Φ_final − Φ_initial	Wb

Step-by-Step Examples

Example 1

Generator Coil

N = 500 turns, flux changes from 0.02 to 0 Wb in 0.01 s.

delta_Phi = 0.02 Wb
EMF = 500 * 0.02 / 0.01 = 1000 V

✓ 1000 V induced — typical generator voltage

Example 2

Transformer Primary

N = 200 turns, flux changes at 0.5 Wb/s.

EMF = 200 * 0.5 = 100 V

✓ 100 V in primary coil

Example 3

Slow Change

N = 50 turns, delta_Phi = 0.1 Wb in 2 s.

EMF = 50 * 0.1 / 2 = 2.5 V

✓ 2.5 V — slow change gives small EMF

Real-World Applications

💡

Electric Generators

Rotating a coil in a magnetic field continuously changes flux, generating AC voltage.

🔌

Transformers

AC creates changing flux in core; Faraday law induces voltage in secondary winding.

💳

Wireless Charging

Changing current in charging pad creates changing flux that induces current in phone coil.

🚗

Ignition Systems

Rapidly collapsing field in ignition coil induces ~20,000 V spark across spark plug.

Common Mistakes to Avoid

⚠️

More turns = more EMF

EMF = N * delta_Phi / delta_t. Doubling turns doubles EMF. This is why coils have many turns.

⚠️

DC does not induce EMF

Constant current = constant flux = delta_Phi/dt = 0 = no EMF. Transformers require AC.

⚠️

Lenz law gives direction

The minus sign in EMF = -N*d_Phi/dt means induced current opposes the flux change. Use right-hand rule for direction.

Frequently Asked Questions

What is Lenz law? ▾

Lenz law states the induced current flows to oppose the change in flux that caused it. It is the physical meaning of the minus sign in Faraday law.

What is 1 Weber? ▾

1 Wb = 1 V*s = 1 T*m^2. Flux of 1 Wb changing at 1 Wb/s induces 1 V in a single-turn coil.

How does a generator work? ▾

Rotating coil in magnetic field: flux = B*A*cos(omega*t), changing sinusoidally. EMF = N*B*A*omega*sin(omega*t). Maximum EMF = N*B*A*omega.

What are eddy currents? ▾

Loops of current induced in solid conductors by changing flux, following Faraday law. They dissipate energy as heat and are reduced by laminating transformer cores.

Is Faraday law one of Maxwell equations? ▾

Yes. Integral form of Maxwell third equation: closed loop EMF = -d/dt * integral of B over surface. The differential form: curl(E) = -dB/dt.

Related Physics Calculators

Formula Explorer connections

Interpretation: This relationship connects magnetic fields, moving charge, flux, induction or electromagnetic material response. Assumption: Specify field direction and sign convention. Uniform fields, linear materials, negligible edge effects or sinusoidal steady state may be assumed.

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