Physics 3 — Electricity & Magnetism
Coulomb’s law, fields, magnetic force on moving charge, the solenoid, and the electromagnetic wave.
Two invisible fields, one unified story. Electric fields push on charges; magnetic fields push only on moving charges; and Maxwell's stunning punchline — a changing one creates the other — turns out to be why light exists. (We work in plain SI numbers here; each line notes its units.)
- 01 Coulomb's law — the inverse square ELI5: two charges push or pull with F = k·q₁q₂/r² — exactly the shape of gravity, but about 10³⁶ times stronger (which is why static cling beats the whole…
- 02 The field — force per unit charge ELI5: instead of asking "what force on this charge?", a field maps what any charge would feel at each point: E = k·q/r² (newtons per coulomb). The…
- 03 Magnetic force — only on the moving ELI5: a magnetic field ignores a parked charge entirely. Let it move, and the field shoves it sideways — perpendicular to both the velocity and the field: F =…
- 04 Making fields: the solenoid ELI5: wrap wire into a tight coil and the current creates a uniform field inside: B = μ₀·n·I. More turns per metre or more current → more field. That coil is…
- 05 The payoff: light ELI5: a changing E makes a B; a changing B makes an E; the disturbance keeps regenerating itself and races off at c = 1/√(μ₀ε₀). Maxwell computed that speed…
next course: Physics 4 — Thermo & Fluids →