Two identical coils of negligible resistance when connected in series across a $$200V,$$ $$50$$ $$Hz$$ source draws, a current of $$10$$ $$A.$$ When the terminals of one of the coils are reversed, then current drawn is $$8$$ $$A.$$ The coefficient of coupling between the two coils is

The primary current in a current transformer is dictated by

In the circuit shown in fig. For measuring resistance $$'R'$$ if the ammeter indicates $$1$$ $$A$$ and the voltmeter indicate $$100V$$, then the value of $$R$$ is ___________ Ohms and the error in measurement using the ratio $$V/$$$${\rm I}$$ is ________%

A dynamometer type wattmeter responds to the