An advantage of a permanent magnet moving coil instrument is that it is

The scale of a voltmeter is uniform. Its type is

For a given frequency, the deflecting torque of an induction ammeter is directly proportional to

A water boiler at home is switched on to the $$A.C$$ mains supplying power at $$230$$ $$V/50$$ $$Hz.$$ The frequency of instantaneous power consumed by the boiler is