Mutual Inductance (ε₂ = -M di₁/dt; M = N₂Φ₂₁/i₁)

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ε₂ = -M di₁/dt; M = N₂Φ₂₁/i₁

What each symbol means

SymbolWhat it stands for
MMutual inductance (H)
i₁Current in primary coil
Φ₂₁Flux through one turn of coil 2 due to i₁

When to use this

Fixed geometry; linear media. M₁₂ = M₂₁ = M for a passive pair.