# How long does it take for a coil with an inductance of 240 mH to increase the current from zero

How long does it take for a coil with an inductance of 240 mH to increase the current from zero to 11.4 A, if an average EMF of self-induction equal to 30 V.

To find out the duration of the current rise in the used coil, we apply the formula: εsi = | -L * ΔI / Δt | = | -L * (I – 0) / Δt | = | -L * I / Δt |, whence we express: Δt = L * I / εsi.

Data: L – inductance of the used coil (L = 240 mH = 0.24 H); I is the current established in the coil (I = 11.4 A); εsi – emerged EMF of self-induction (εsi = 30 V).

Let’s calculate: Δt = L * I / εsi = 0.24 * 11.4 / 30 = 0.0912 s or 91.2 ms.

Answer: The current rise in the used coil occurred in 91.2 ms.

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