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Inductors - Engineering

Q1:

Two inductors, L1 and L2, are in parallel. L1 has a value of 25 H and L2 a value of 50 H. The parallel combination is in series with L3, a 20 H coil. The entire combination is across an ac source of 60 Vrms at 300 kHz. The total rms current is

A 87 mA

B 870 mA

C 87 A

D 337 mA

ANS:B - 870 mA

1. L1 parallel with L2, which is ( 25 micro * 50 micro)/( 25 micro + 50 micro) = 16.67 micro Henry.

2. L1 and L2 parallel value series with L3 which is ( 16.67 Micro + 20 Micro) = 36.67 micro Henry.

So now put into the formula,

I rms= Vrms / 2*pai *F*L.

= 60/( 2*pi*300K*36.67 micro).
=0.87 A.
= 870 mA.