What is electromagnetic induction?

Electromagnetic induction (discovered by Michael Faraday, 1831): a changing magnetic field through or near a conductor INDUCES a voltage in the conductor. If the conductor is part of a circuit, this induced voltage drives a current. Faraday's Law: EMF = -N × dΦ/dt, where N is number of turns, Φ is magnetic flux, and t is time. Negative sign reflects Lenz's Law: induced current opposes the change causing it. Key principle: the magnetic field must be CHANGING (relative to the conductor) for induction. Three ways to create a changing field: (1) Move the conductor through a stationary field; (2) Keep the conductor still, move the field source; (3) Change the field strength while conductor is stationary (e.g., AC current in a nearby coil). Applications: (1) GENERATORS — rotate a coil through a magnetic field (or rotate a magnet near a coil); produces AC; the foundation of nearly all electricity generation (coal, gas, hydro, nuclear, wind — they all spin a generator); (2) TRANSFORMERS — AC in primary creates changing field; secondary coil sees changing field; voltage induced; (3) ELECTRIC MOTORS — opposite of generators (apply electrical energy to produce rotation); current in coil within magnetic field experiences force; (4) WIRELESS CHARGING — varying magnetic field induces voltage in coil of receiving device; (5) GUITAR PICKUPS — vibrating steel guitar string in magnetic field of pickup coil induces signal in coil; (6) METAL DETECTORS — coils create field; metal disturbs field; second coil detects disturbance; (7) INDUCTION COOKTOPS — varying magnetic field induces current in iron/steel pan, heating it directly (the pan is the conductor); (8) MAGNETIC TAPE/HARD DRIVE READING — moving magnetized surface past a read head induces signals. Magnetic flux is measured in Webers (Wb); flux density in Tesla (T). Magnetic field around a current-carrying wire: right-hand rule predicts direction (thumb in direction of current, fingers curl in direction of magnetic field).