AC Fundamentals, Circuit and Circuit Theory
The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of

Skin effect
Increase in temperature
Iron loss in core
Capacitive effect between adjacent coil turns

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AC Fundamentals, Circuit and Circuit Theory
The phase difference between voltage and current wave through a circuit element is given as 30°. The essential condition is that

Both waves must have identical peak values
Both waves must have zero value at the same time
Both waves must have same frequency
None of the listed here

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