Question

A 50 Hz voltage is measured with a moving iron voltmeter and a rectifier type AC voltmeter connected in parallel. If the meter readings are VA and VB respectively. Then the form factor may be estimated as?

(a) \(\frac{V_A}{V_B}\)

(b) \(\frac{1.11V_A}{V_B}\)

(c) \(\frac{\sqrt{2} V_A}{V_B}\)

(d) \(\frac{πV_A}{V_B}\)

The question was asked by my school teacher while I was bunking the class.

My query is from Advanced Problems on Magnetically Coupled Circuits in portion Resonance & Magnetically Coupled Circuit of Network Theory

Answer 1

The correct answer is (b) \(\frac{1.11V_A}{V_B}\)

For explanation I would say: Form factor of the wave = \(\frac{RMS \,value}{Mean \,value}\)

Moving iron instrument will show rms value. Rectifier voltmeter is calibrated to read rms value of sinusoidal voltage that is, with form factor of 1.11.

∴ Mean value of the applied voltage = \(\frac{V_B}{1.11}\)

∴ Form factor = \(\frac{V_A}{V_B/1.11} = \frac{1.11V_A}{V_B}\).