§7.2 Faraday’s law Christopher Crawford PHY

Outline Faraday’s law – THREE experiments, one result – EMF, Lenz’ law, special relativity – Examples: AC generator, solenoid & ring, SC levitation Differential form – THREE Ampère-like laws, one form – Magnetic vector potential: potential momentum Mutual inductance – transformers, inductors – Example: overlapping solenoids Inductor – THREE electrical devices, one calculation – Example: L–R circuit Magnetic field energy – back EMF or “electrical inertia” – Compare: electrical field energy 2

Faraday’s law – THREE experiments 3

Example: AC generator 4

Example: solenoid and ring What is I(t) in the ring? Which direction? Levitation of ring Permanent for superconductors 5

THREE Ampère-like laws Ampère’s law Vector potentialFaraday’s law Relation between E and A: will need to revisit electric potential! 6

Mutual Inductance Overlapping solenoid and ring: mutual inductance M Self-inductance L 7

Inductance – 1 of THREE components CapacitorResistorInductor Each the ratio of FLUX / FLOW Units: Complex impedance: 8

Example – LR-circuit 9

Magnetic field energy Work against the “back-EMF” is stored in the magnetic field It acts as “electrical inertia” to keep current moving 10