# Inductance of a Coil

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One of the coils we use in class has 157 turns in 18 cm and a cross section area of 5.0 * 10^-3 m^2. (a) What is its inductance L, and (b) What self-induced emf will it produce at 100 ms if the current through it changes as shown in this graph?

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## SOLUTION This solution is **FREE** courtesy of BrainMass!

a) Inductance L of a coil is given by : L = (uo)N^2A/l where uo = permeability of free space, N = Total number of turns, A = cross sectional area and l = length of the coil.

Substituting values we get : L = 4pi x 10^-7 x 157^2 x 5 x 10^-3/0.18 = 0.86 x 10^-3 H or 0.86 mH

b) At 100 ms the rate of change of current as given by the slope of current vs time graph is (2.5 A)/(200ms) or 2.5/0.2 = 12.5 A/sec.

Magnitude of self induced emf = LdI/dt = 0.86 x 10^-3 x 12.5 = 10.75 x 10^-3 Volts or 10.75 mV

Â© BrainMass Inc. brainmass.com December 24, 2021, 7:58 pm ad1c9bdddf>https://brainmass.com/physics/emf/inductance-coil-234025