A 25 mV, 2 mA D'Arsonval movement is to be used in a voltmeter having a full-scale reading of 100 V. Find the total internal resistance of this 100 V voltmeter.

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.