Question

For a certain dynamometer ammeter the mutual inductance (M) varies with deflection θ° as M = -6 cos (θ + 30°) mH. Find the deflecting torque produced a direct current of 50 mA corresponding to a deflection of 60°.
1. 10 N-m
2. 20 N-m
3. 15 μN-m
4. 1.5 μNm

Answer 1

Correct Answer - Option 3 : 15 μN-m

\({T_d} = {I^2}\left( {\frac{{dM}}{{d\theta }}} \right)\)

\(= 2500 \times {10^{ - 6}} \times \frac{d}{{d\theta }}\left( { - 6\cos \theta + 30^\circ } \right) \times {10^{ - 3}}\)

\(= 15\;\mu N - m\)