Question

A coil is designed for high Q performance at a rated voltage and a specified frequency. If the frequency is made twice the original and the coil is operated at the same rated voltage, then the active power P will be affected as ____________ (a) P is halved (b) P remains unchanged (c) P is doubled (d) P decreases 4 times The question was asked in final exam. Origin of the question is Advanced Problems on Magnetically Coupled Circuits topic in division Resonance & Magnetically Coupled Circuit 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

Correct choice is (d) P decreases 4 times Explanation: I1 = \frac{V}{\sqrt{R^2+ ω_1^2 L^2}} = \frac{V}{ω_1 L} For a high current coil, ωL >> R I2 = \frac{V_1}{2ω_1 L} = \frac{I_1}{2} ∴ P2 = R (\frac{I_1}{2} )^2 = \frac{P_1}{4} Therefore, P decreases 4 times.