The four stator conductors (A, A', B and B') of a rotating machine are carrying DC currents of the same value, the directions of which are shown in the figure (i). The rotor coils $$a$$-$$a'$$ and $$b$$-$$b'$$ are formed by connecting the back ends of conductors '$$a$$' and '$$a'$$' and '$$b$$' and '$$b'$$', respectively, as shown in figure (ii). The e.m.f. induced in coil $$a$$-$$a'$$ and coil $$b$$-$$b'$$ are denoted by $${E_{a - a'}}$$ and $${E_{b - b'}}$$, respectively. If the rotor is rotated at uniform angular speed $$\omega$$ rad/s in the clockwise direction then which of the following correctly describes the $${E_{a - a'}}$$ and $${E_{b - b'}}$$?

A separately excited DC motor rated 400 V, 15 A, 1500 RPM drives a constant torque load at rated speed operating from 400 V DC supply drawing rated current. The armature resistance is 1.2 $$\Omega$$. If the supply voltage drops by 10% with field current unaltered then the resultant speed of the motor in RPM is ____________ (Round off to the nearest integer).

A three-phase synchronous motor with synchronous impedance of 0.1+j0.3 per unit per phase has a static stability limit of 2.5 per unit. The corresponding excitation voltage in per unit is _________ (Round off to 2 decimal places).

A three phase 415 V, 50 Hz, 6-pole, 960 RPM, 4 HP squirrel cage induction motor drives a constant torque load at rated speed operating from rated supply and delivering rated output. If the supply voltage and frequency are reduced by 20%, the resultant speed of the motor in RPM (neglecting the stator leakage impedance and rotational losses) is ___________ (Round off to the nearest integer).