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Lenz's law determines the direction of induced current: it opposes the change in flux that caused it. This is encoded in the negative sign of Faraday's law and is fundamentally a statement of energy conservation — work must be done against the induced current's opposition to maintain the flux change.
Practical applications: (1) Bar magnet approaching coil (N-pole first) — coil's near face becomes N (repels). (2) Bar magnet receding — near face becomes S (attracts). (3) Flux increasing into the page — induced current flows counterclockwise (creates out-of-page field). (4) Flux decreasing — current flows clockwise (supports the decreasing field).
Physical consequences of Lenz's law include: electromagnetic braking (eddy currents in metals oppose relative motion), the "jumping ring" experiment (ring repelled from energizing solenoid), and the slow fall of a magnet through a conducting tube.
Common errors: (1) Confusing "opposing the flux" with "opposing the field" — the current opposes the change in flux, not the flux itself. If flux is decreasing, the current supports the existing field. (2) Forgetting that Lenz's law gives direction only — use Faraday's law for magnitude.