FAA Aviation Mechanic General (AMG)Fundamentals of Electricity and ElectronicsHard
A technician moves a bar magnet's north pole toward a stationary closed coil of wire, inducing a current in the coil. According to Lenz's Law, what determines the direction of the induced current?
- AThe induced current direction is random and cannot be predicted
- BThe induced current always flows from north to south through the external circuit
- CThe induced current flows in the direction that opposes the change in magnetic flux through the coil
- DThe induced current flows in the direction that aids the increasing magnetic flux from the magnet
Show answer & explanationAnswer & explanation
Correct answer: C. The induced current flows in the direction that opposes the change in magnetic flux through the coil
Lenz's Law states that the induced current will flow in a direction that creates a magnetic field opposing the change in flux that produced it, consistent with the conservation of energy. As the magnet approaches, the coil's induced current opposes the increasing flux.
Why the other options are wrong
- A. Induced current direction is predictable and governed by Lenz's Law, not random.
- B. Current direction depends on the coil's winding and flux change, not a fixed north-to-south rule.
- D. This would violate the conservation of energy by aiding rather than opposing the change.
Lenz's Law
Lenz's Law states that an induced current always flows in a direction that opposes the change in magnetic flux that created it, consistent with conservation of energy.
- Induced current opposes the change causing it
- Based on conservation of energy
- Complements Faraday's Law which gives magnitude of induced EMF
Memory trick: 'Lenz Resists the Change' - nature opposes what disturbs it.