Kelvin double bridge is best suited for the measurement of

Two in-phase, 50Hz sinusoidal waveform of unit amplitude are fed into channel-1. and channel-2 respectively of an oscilloscope, Assuming that the voltage scale, time scale and other settings are exactly the same for both the channels. What would be observed if the oscilloscope is operated in x-y mode?

The line to line input voltage to the $$3$$ phase, $$50$$ Hz, ac circuit shown in fig is $$100$$ $$V$$ $$r.m.s$$ Assuming that the phase sequence is $$RYB$$ the wattmeter would read.

A $$415$$ $$V,$$ $$2$$ pole, $$3$$ phase, $$50$$ $$Hz,$$ star connected, non-salient pole synchronous motor has synchronous reactance of $$2\,\Omega $$ per phase and negligible stator resistance. At a particular field excitation, it draws 20 A at unity power factor from a $$415$$ $$V,$$ $$3$$ phase, $$50$$ $$Hz$$ supply. The mechanical load on the motor is now increased till the stator current is equal to $$50$$ $$A.$$ The field excitation remains unchanged. Determine:
$$(a)$$ the per phase open circuit voltage $${E_0}$$
$$(b)$$ the developed power for the new operating condition and corresponding power factor.