A moving-coil voltmeter has a coil with 100 turns, and is 4 cm long and 3 cm wide. If it carries 25 mA of current and the flux density in the air gap is 0.06 Wb/m2, find the deflecting torque.

A D'Arsonval galvanometer has flux density = 8 × 10-3 Wb/m2, number of turns = 300, length of coil = 15 mm, width of coil = 30 mm, spring constant = 2.5 × 10-9 Nm/rad, moment of inertia = 10 × 10-9 kg-m2, damping constant = 2 × 10-9 Nm/rad-s-1, and resistance of coil = 80 Ω. What is the deflection of the galvanometer for a current of 1 μA?

A 5 A ammeter has an internal resistance of 0.1 Ω. What value of shunt resistance is required to extend its range to 25 A?