GATE EE 2015 Set 2 — Question 15

MCQ+1 / -0.33EasyPMMC & Moving IronElectrical Quantity MeasurementElectrical & Electronic MeasurementsDynamometer Instruments

Electrical & Electronic Measurements → Electrical Quantity Measurement → Dynamometer Instruments

Last updated 5 September 2026

Question

Match the following. Instrument Type Used for P. Permanent magnet moving coil 1. DC Only Q. Moving iron connected through current transformer 2. AC Only R. Rectifier 3. AC and DC S. Electrodynamometer

Instrument Type	Used for
P. Permanent magnet moving coil	1. DC Only
Q. Moving iron connected through current transformer	2. AC Only
R. Rectifier	3. AC and DC
S. Electrodynamometer

Correct answer (C) P-1, Q-2, R-3, S-3 Solution The matching is based on the operating principles of electrical instruments: P. Permanent magnet moving coil (PMMC) : These instruments respond to the average value of current. In AC, the average value is zero, so they are used for DC Only (P-1). Q. Moving iron (MI) connected through current transformer (CT) : While MI instruments can measure both AC and DC, current transformers (CTs) operate on the principle of electromagnetic induction, which requires a time-varying flux. Thus, CTs do not work on DC, making the combination suitable for AC Only (Q-2). R. Rectifier instruments : These convert AC to DC to be measured by a PMMC. They can be used for both AC and DC measurements (R-3). S. Electrodynamometer : These instruments use the interaction of magnetic fields from two coils. Since the current in both coils reverses simultaneously in AC, the torque remains unidirectional. They are used for both AC and DC (S-3). Matching: P-1, Q-2, R-3, S-3. This corresponds to option (C). Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (C) P-1, Q-2, R-3, S-3 Solution The matching is based on the operating principles of electrical instruments: P. Permanent magnet moving coil (PMMC) : These instruments respond to the average value of current. In AC, the average value is zero, so they are used for DC Only (P-1). Q. Moving iron (MI) connected through current transformer (CT) : While MI instruments can measure both AC and DC, current transformers (CTs) operate on the principle of electromagnetic induction, which requires a time-varying flux. Thus, CTs do not work on DC, making the combination suitable for AC Only (Q-2). R. Rectifier instruments : These convert AC to DC to be measured by a PMMC. They can be used for both AC and DC measurements (R-3). S. Electrodynamometer : These instruments use the interaction of magnetic fields from two coils. Since the current in both coils reverses simultaneously in AC, the torque remains unidirectional. They are used for both AC and DC (S-3). Matching: P-1, Q-2, R-3, S-3. This corresponds to option (C).

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