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.

T_{D} 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:

T_{c} = k θ ----(2)

At equilibrium,

T_{d} = T_{c }-----(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:

\(\theta = 2.18 \times \frac{{180^\circ }}{\pi } = 125^\circ \)