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Direction of induced emf under Lenz's Law

Aviation Mechanic General (AMG) practice question 6 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.K7f · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONAccording to Lenz's Law, the emf induced in a circuit always acts in a direction such that the current it produces creates a magnetic field that does what?

  1. AReinforces the change in magnetic flux
  2. BOpposes the change in magnetic flux
  3. CCancels the resistance of the coil windings
Show the answer and explanation

Correct answer: B. Opposes the change in magnetic flux

  • A — incorrect The induced field opposes, not reinforces, the change in flux; reinforcing it would violate the law.
  • B — correct Lenz's Law states that the induced emf drives a current whose magnetic field opposes the change in magnetic flux that produced it.
  • C — incorrect Lenz's Law concerns the direction of the induced emf relative to the changing flux; it has nothing to do with the resistance of the windings.

BACKGROUND

Faraday's Law states that the emf induced in a closed loop of wire is proportional to the rate of change of the magnetic flux through the coil. Lenz's Law, summarized by the German physicist Heinrich Lenz in 1833, gives the direction of that induced emf: it always acts so that the current it drives produces a magnetic field opposing the change in magnetic flux. This is why an inductor opposes any change in the current through it. The self-induced voltage in a coil, called self-inductance, counters the immediate establishment of maximum current when a circuit is first energized.

STUDY TIP

Pair Faraday's Law (how much emf) with Lenz's Law (which direction) so you can tell the two apart on the test.

KEY POINTS

  • Lenz's Law gives the direction of an induced emf.
  • The induced current's magnetic field opposes the change in flux that caused it.
  • This opposition is the reason inductors resist changes in current.

SOURCES

  • FAA-H-8083-30B ch12 "Self-Inductance" (Lenz's Law statement)
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.