Question

A rectifier type AC voltmeter consists of a series resistance R, an ideal full-wave rectifier bridge and a PMMC instrument. A DC current of 1 mA produces a full-scale deflection of the instrument. The resistance of the instrument is 100 Ω. A voltage of 100 V (rms) is applied to the input terminals. The value of R required is? (a) 63.56 Ω (b) 89.83 Ω (c) 89.83 kΩ (d) 141.3 kΩ I had been asked this question by my college professor while I was bunking the class. Question is taken from Problems Involving Standard Time Functions in division Application of the Laplace Transform in Circuit Analysis of Network Theory Select the correct answer from above options network theory questions and answers, network theory questions pdf, network theory question bank, network theory gate questions and answers pdf, mcq on network theory pdf, gate network theory questions and solutions, network theory mcq Test , ies network theory questions, Network theory Questions for GATE EC Exam, Network Theory MCQ (Multiple Choice Questions)

Answer 1

The correct choice is (c) 89.83 kΩ The explanation: VOAverage = 0.636 × \sqrt{2} Vrms = 0.8993 Vrms The deflection with AC is 0.8993 times that with DC for the same value of voltage V SAC = 0.8993 SDC SDC of a rectifier type instrument is \frac{1}{I_{fs}} where Ifs is the current required to produce full scale deflection, Ifs = 1 mA; Rm = 100 Ω; SDC = 10^3 Ω/V SAC = 0.8993 × 1000 = 899.3 Ω/V. Resistance of multiplier RS = SAC V – Rm – 2Rd, where Rd is the resistance of diode, for ideal diode Rd = 0 ∴ RS = 899.3 × 100 – 100 = 89.83 kΩ.