A moving coil instrument with a resistance of 20 Ω gives a full-scale deflection at 50 mA. How can this meter be modified to measure a total current of up to 5 A?

A wattmeter has pressure coil ranges of 500/250/125 V and current coil ranges of 20/10/5 A. The full scale deflection (FSD) of the meter is 625 W. Determine the multiplying factor (meter constant) when connected to 500 V and 10 A range.

A permanent magnet moving coil (PMMC) instrument has a coil of dimensions 15 mm × 12 mm. The flux density in the air gap is 1.8 × 10-3 Wb/m2 and the spring constant is 0.14 × 10-6 N·m/rad. Determine the number of turns required to produce an angular deflection of 90° when a current of 5 mA is flowing through the coil.