Answer: A steady current produces no changing magnetic flux.
- A A steady current produces no changing magnetic flux
- B A steady current produces excessive output voltage
- C A steady current always reverses the magnetic field
- D A steady current makes the secondary resistance zero
Correct answer: A. A steady current produces no changing magnetic flux
Explanation: A transformer requires changing magnetic flux to induce an emf in the secondary coil. A steady DC current produces steady flux after the switching transient, so no continuous secondary emf is induced.
In a pure inductor the current lags the voltage by 90° (energy is briefly stored in the magnetic field before current responds); in a pure capacitor the current leads the voltage by 90° (current must flow to build up charge before voltage rises) - the mnemonic "ELI the ICE man" keeps these straight.
Concept context
AC circuits, impedance, LCR series circuit, resonance, transformers, and power factor.