Correct Answer - Option 2 : 125°
Concept:
Deflecting torque:
It is proportional to quantity under measurement, this torque deflects the pointer away from initial or zero position.
TD Measurable quantity.
For electrodynamometer, deflecting Torque is defined as:
\({T_D} = {I^2}\frac{{dm}}{{d\theta }}\) ---(1)
Controlling Torque:
It is opposite to the deflecting Torque when deflecting Torque equals to the controlling Torque Pointer comes to a final steady-state position.
For electrodynamometer, controlling Torque is defined as:
Tc = k θ ----(2)
At equilibrium,
Td = Tc -----(3)
Calculation:
Given:
\(\frac{{dm}}{{d\theta }} = 0.0035\mu H/degree\)
K = 10-6 Nm/degree
From equation (1), (2), (3), we get:
\(K\theta = {I^2}\frac{{dm}}{{d\theta }}\)
\(\theta = \frac{{{I^2}}}{K}\frac{{dm}}{{d\theta }}\)
\(\theta = \frac{{{{\left( {25} \right)}^2}}}{{{{10}^{ - 6}}\frac{{Nm}}{{degree}}}} \times 0.0035 \times {10^{ - 6}}\frac{H}{{degree}}\)
= 2.18 rad
Converting radian into the degree, we get:
\(\theta = 2.18 \times \frac{{180^\circ }}{\pi } = 125^\circ \)