AC Generator (Dynamo)
- Rotating coil in magnetic field; commutator replaced by slip rings for AC output
- EMF: ε = NBAω sin(ωt); peak EMF = NBAω
- Application: Power plants (hydro, thermal, nuclear all use generators)
Electric Motor (Reverse of Generator)
- Current-carrying coil in field → torque → rotation (F = BIl × lever arm)
- Back-EMF induced opposes applied voltage (energy conservation)
- Application: Fans, pumps, electric vehicles, industrial machinery
Transformer
- Step-up: Power transmission at high voltage (440 V → 11 kV → 220 kV) to minimize R losses
- Step-down: Household supply (220 kV → 11 kV → 440 V → 220 V)
- Power loss in transmission ∝ × R; high V → low I → low loss
Eddy Current Applications
| Application | Principle |
|---|---|
| Induction furnace | Large eddy currents heat metal for melting/welding |
| Electromagnetic braking | Eddy currents in rotating disk create opposing (braking) force — used in trains |
| Speedometer | Rotating magnet induces eddy currents in aluminum drum; drag proportional to speed |
| Induction cooktop | Eddy currents induced in ferromagnetic cookware generate heat |
| Metal detector | Eddy currents change when conductive object present |
Minimizing Eddy Currents
- Lamination: Thin sheets with insulating varnish break eddy current paths
- Used in transformer cores, motor/generator cores, relay cores
Induction Motor
- Rotating magnetic field induces eddy currents in rotor → rotor follows the field
- No electrical connection to rotor (brushless)
- Application: Industrial motors (>90% of industrial motors worldwide)