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Circuit and electromagnetism basics

When the magnetic flux through a coil changes, an EMF is induced in the coil (electromagnetic induction). Which determines the magnitude of this induced EMF?

  1. AThe magnitude of the flux at that instant
  2. BThe resistance of the coil's wire
  3. CThe rate of change of the flux and the number of turns in the coil
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Answer: C. The rate of change of the flux and the number of turns in the coil

By Faraday's law of induction, the induced EMF is e = N × ΔΦ/Δt, proportional to the number of turns N and the rate of change of flux. A large but unchanging flux induces no EMF. The wire's resistance affects how much current the EMF drives but does not set the EMF itself. Generators, transformers and induction cooktops all rely on this principle.

  • A. A large flux that does not change induces no EMF.
  • B. Resistance affects the resulting current, not the size of the EMF.
  • C. Correct. e = N × ΔΦ/Δt, proportional to the rate of change and the number of turns.
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