Question

In a moving iron meter, the deflection torque is proportional to?

(a) Square of the current through the coil

(b) Current through the coil

(c) Sine of measurand

(d) The Square root of the measurand

This question was addressed to me during an interview.

This intriguing question originated from Advanced Problems on Indicating Instruments in portion Extension of Instrument Ranges of Electrical Measurements

Answer 1

Right answer is (a) Square of the current through the coil

Explanation: We know that,

Td = \(\frac{1}{2} I^2 \frac{dl}{dθ} \)

∴ The deflection torque is proportional to the square of the current through the coil.