Question

In the circuit given below, the voltage across the 18 Ω resistor is 90 V. The voltage across the combined circuit is _________ (a) 125 V (b) 16 V (c) 24 V (d) 40 V This question was posed to me during an interview. Query is from Advanced Problems on Network Theory in section Network Theory and Complex Circuit Diagram 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 (a) 125 V For explanation I would say: Current through the 18 Ω resistance = \frac{90}{18} = 5 A Equivalent resistance of 3 Ω and 7 Ω banks = \frac{3 × 6}{3 + 6} = 2 Ω Since, this 2 Ω resistance is in series with 18 Ω resistance, therefore total resistance = 18 + 2 = 20 Ω This 20 Ω resistance is in parallel with 5 Ω resistance = \frac{5 × 20}{5 + 20} = 4 Ω Hence, total resistance of the circuit = 1 + 4 = 5 Ω Current through this branch = 5 A ∴ Voltage across dc= 5 × 20 = 100 V Hence current through 5 Ω resistance = \frac{100}{5} = 20 A ∴ Total current = 20 + 5 = 25 A Since, total resistance of the circuit is 5 Ω therefore, voltage E = 25 × 5 = 125 V.