History of Electricity & Magnetism – Quick Review

Electromagnetism Overview

  • Unified interaction of electric charges, magnetic moments, and electromagnetic fields
  • Moving charges generate magnetic fields; varying magnetic fields induce electric currents

Forms of Electricity

  • Static (Electrostatics): charges at rest; e.g., rubbed amber, lightning
  • Dynamic (Electrodynamics): charges in motion (current), produced by magnetism, chemicals, light, heat, or pressure

Essential Quantities & Components

  • Current: flow of electrons through a conductor
  • Capacitor: stores charge on two plates
  • Conductors: silver, gold, copper, steel, sea water
  • Insulators: rubber, glass, oil, diamond, dry wood
  • Semiconductors: silicon, germanium, gallium arsenide (conductivity between insulator & metal)

Core Laws & Equations

  • Ohm’s Law: V=IRV = IR
  • Coulomb’s Law: F=kq<em>1q</em>2r2F = k \dfrac{q<em>1 q</em>2}{r^2}
  • Ampère’s Circuital Theorem: ∮B⃗⋅dl⃗=μ0I\oint \vec{B} \cdot d\vec{l} = \mu_0 I
  • Faraday’s Law of Induction: E=−dΦBdt\mathcal{E} = - \dfrac{d\Phi_B}{dt}
  • Lenz’s Law: induced current opposes the change that produces it
  • Photon energy–frequency relation: E=hf=hcλE = h f = \dfrac{h c}{\lambda}

Lightning Snapshot

  • Charge separation in clouds: positive top, negative base
  • Discharges: intra-cloud, inter-cloud, cloud-to-ground
  • Typical potential difference ≈ 109 V10^9\,\text{V}

Historical Timeline (Key Milestones)

  • 2635 BC – Hoang-Ti uses lodestone compass
  • 600 BC – Thales observes static electricity on amber
  • 1492 – Columbus notes compass declination
  • 1600 – Gilbert coins “electricity”; Earth as giant magnet
  • 1729 – Gray distinguishes conductors & insulators
  • 1733 – Du Fay: positive vs. negative charges
  • 1745 – Cuneus & Muschenbrock invent Leyden jar (first capacitor)
  • 1752 – Franklin proves lightning is electrical; lightning rod
  • 1771 – Galvani discovers bio-electricity (frog legs)
  • 1785 – Coulomb quantifies electric forces
  • 1800 – Volta constructs voltaic pile (first battery)
  • 1819 – Oersted links electric current to magnetic field
  • 1820 – Ampère quantifies magnetic force from current
  • 1827 – Ohm formulates V=IRV=IR
  • 1831 – Faraday builds first generator; discovers induction
  • 1833 – Lenz articulates opposition principle
  • 1830s – Henry: electromagnetic motor & induction
  • 1860s – Maxwell mathematically unifies electromagnetism
  • 1876 – Bell patents telephone (electrical speech transmission)
  • 1879 – Edison commercializes electric light & power systems
  • 1886 – Hertz detects electromagnetic waves (radio basis)
  • 1888 – Tesla develops AC induction motor & Tesla coil
  • 1901 – Marconi achieves trans-Atlantic wireless telegraphy

Electronics Evolution

  • 1887 onward: electronics diverges from classical electricity (vacuum tubes → transistors → robotics)