10 cm has the dimensions as given in Figure . Calculate the limit value of the current in the

series-connected coils so that the electromagnet can lift the ferromagnetic bar having a relative

permeability of 300 and a mass of 20 kg (Earth’s gravitational constant g=9.81 m/s2).

2-

Consider the two-coil rotating electromechanical system shown in Figure. The

airgap is uniform and the iron core is infinitely permeable. The self inductance of the rotor and

stator coils are Lr = Ls = 0.6 H, and the mutual inductance between them varies with the angular

position (θ) as: Lrs(θ) = Lsr(θ) = 0.5 cos θ, where θ is in degrees.

a) Calculate the torque induced on the rotor when θ = 30o, Is = 5 A and Ir = 2 A, where Is

and Ir are currents in stator and rotor coils, respectively.

b) The rotor coil is open circuited and the stator coil current is fixed to 5 A. Calculate

induced voltage between the terminals of the rotor coil when the rotor is revolving at an

angular speed of 100 rad/s.