Formulas & tables/Physics/Magnetism and induction/Induced EMF (Faraday's law)

Induced EMF (Faraday's law)

ε=−ΔΦΔt\varepsilon=-\dfrac{\Delta\Phi}{\Delta t}

Result unit: V (volt)

What it describes

Faraday's law — a change in magnetic flux induces an EMF; the minus sign (Lenz's rule) means it opposes the change.

Symbols

ε\varepsilon
electromotive force
[V]
ΔΦ\Delta\Phi
change in magnetic flux
[Wb]
Δt\Delta t
time
[s]

Where it comes from

A change in the magnetic flux through a circuit produces a voltage (EMF) — the faster the change, the greater the EMF. The minus sign (Lenz's rule) says the induced current opposes that change.

When to use it

Generators, transformers, induction — the basis of generating electricity.

Example

The magnetic flux changes by 0.2 Wb in 0.1 s. Calculate the EMF.
SubstitutionΔΦ=0.2\Delta\Phi=0.2 Wb, Δt=0.1\Delta t=0.1 s.
Result∣ε∣=0.20.1=2|\varepsilon|=\dfrac{0.2}{0.1}=2 V.

Related formulas

Force on a current-carrying conductor Frequency of an LC circuit

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