ConceptElectromagnetism
← All conceptsElectromagnetic induction
magnetic flux Φ=BA cos(θ), Faraday's law EMF=n·dΦ/dt, Lenz's law (induced effect opposes the CHANGE in flux, oppose ≠ reverse), motional EMF=BLv, four-step induced-current-direction method
11 ways this goes wrong. Each one is a named misconception the questions are built to catch.
- EMF proportional to fluxSets the induced EMF proportional to the flux itself rather than to its rate of change dΦ/dt.→
- Flux angle measured from planeMeasures the angle in Φ=BA cos(θ) from the coil's plane instead of from its normal, swapping where the maximum and zero flux occur.→
- Flux ignores orientationUses Φ=BA and drops the cos(θ) factor for a coil whose normal is not aligned with the field.→
- Induced force aids the motionHas the induced force push the magnet or conductor along its motion, implying the system speeds itself up for free.→
- Lenz 'oppose' read as 'reverse'Treats Lenz's law as opposing the existing flux/field itself rather than opposing the CHANGE in flux, so the induced current direction is wrong when flux is decreasing.→
- Lenz's-law direction wrongGives an induced current that aids the flux change rather than opposing it, violating Lenz's law.→
- Motional EMF formula wrongUses the wrong combination for a moving rod, e.g. EMF=B/Lv or BLv2 instead of BLv.→
- Motional EMF ignores mutual perpendicularityApplies EMF=BLv when B, L, and v are not mutually perpendicular, omitting the angle factor for the component that actually cuts field lines.→
- Steady flux induces currentPredicts an induced EMF or current when the flux is constant (e.g. a stationary coil in a steady field).→
- Turns ignored in coil EMFForgets the factor n (number of turns) when computing the EMF of a multi-turn coil.→
- Wrong viewing side for induced currentStates the induced current sense (clockwise/anticlockwise) without fixing a consistent viewing direction relative to the field, flipping the answer.→
