Describe briefly the effect of varying excitation upon the armature current and power factor of a 3-$\phi$ synchronous motor when the input power to the motor is kept constant.

Find currents I and I₁ in the following circuit.

Determine the Thevenin's equivalent circuit at terminal X-Y of the following circuit.

State maximum power transfer theorem.

If the switch in the following circuit opens at t = 0, find v(t) for t≥ 0 and the initial energy stored in the capacitor.

Show that a series RL circuit is a low pass filter if the output is taken across the resistor. Calculate the cut-off frequency (f_c) if L = 2 mH and R = 10 kΩ.