Question

The mutual inductance of a 25-A electrodynamic ammeter changes uniformly at a rate of 0.0035 μH/degree. The torsion constant of the controlling spring is 10^{− 6} N-m per degree. Determine the angular deflection for full-scale.

Answer 1

By torsion constant is meant the deflecting torque per degree of deflection. If full scale deflecting is θ degree, then deflecting torque on full-scale is 10^{− 6} × θ N^-m.

Now, T_d = I² dM/dθ Also, I = 25 A 

dM/dθ = 0.0035 × 10^{− 6} H/degree 

= 0.0035 × 10^{− 6} × 180/π H/radian

10^{− 6} × θ = 252 × 0.0035 × 10^{− 6} × 180/π

∴ θ = 125.4°