EXTRA QUESTION

Question

The moving coil of a permanent-magnet voltmeter is made of copper and has a resistance of 5Q when at 20°C. The instrument is connected in series with a resistance, the value of which is 995ft at 20°C. Calculate the percentage error, high or low, of the reading at 50°C, if the series resistance is made of (a) copper and (b) manganin. Take the temperature coefficient of copper as 0.004 28/°C at 0°C and that of manganin as zero.

Question

A parallel circuit consists of a branch A of resistance 10Q, inductance 38mH and capacitance 312.8μF, and a branch B of negligible resistance and inductive reactance of 1212. Derive graphically, the total current and its phase angle, if the system is connected to a 440V, 50Hz supply.

Question

The armature and field resistances of a 220V shunt motor are 0.25 and 110 ohms respectively and, when running on no load, the motor takes 6A. Calculate the losses attributable to iron, friction and windage and, assuming this value to remain constant on all loads, determine the efficiency when the current supplied is 62A.

Question