A moving coil voltmeter with a resistance of 20Ω gives full scale deflection of 1200 when
a potential difference of 100mv is applied across it. The moving coil has dimensions of 30mm x
25mm and is wound with 100 turns. The control spring constant is 0.378 x 10-6Nm/degree. Find
(a) Flux density in the gap
(b) Diameter of copper wire of coil winding if 30 percent of instrument resistance is due to coil
winding.
The specific resistance for copper, e = 1.7 x 10-8 Ωm
