The inductors of two L R circuits are placed next to each other, as shown in the figure. The values of the…

The inductors of two LR circuits are placed next to each other, as shown in the figure. The values of the self-inductance of the inductors, resistances, mutual-inductance and applied voltages are specified in the given circuit. After both the switches are closed simultaneously, the total work done by the batteries against the induced EMF in the inductors by the time the currents reach their steady-state values is_______mJ.

Solution

ε1=L1di1dt+Mdi2dt

dW1=ε1i1dt

=L1di1i1+Mdi2i1

dW2=L2di2i2+Mdi1i2

dW1+dW2=L1i1di1+L2i2di2+Mdi1·i2

W=12L1i12+12L2i22+M1i2

=55 mJ,

Note : If mutual induction is taken in opposite direction then W=35 mJ

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Asked in: JEE Advanced 2020 (Paper 2)

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