←All concepts
Concept · Electromagnetism
Electromagnetic 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
Switches you to Physics
Named traps
11 ways this goes wrong.
Each is a named misconception the questions are built to catch. Open one for the move that tempts, and the fix.
- 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.→
Key formulas
No formula sheet is matched to this concept yet. Work it from first principles, and watch the traps.
Shaky underneath?
If the concept underneath still feels loose, patch it here before coming back to CSCA questions.
FoundationsPhysics 2 breadthMechanics foundations