J

9/15/25 Fon Lecture (fields)

  • You can characterize an elementary particle

    • mass, charge, spin, etc.

      • interactions on different fields

  • Our universe is based off of two charges (positive and negative)

  • electrons represent an excitation in the electrical field

  • e = 1.63 × 10-19 C

    • 1 C = 6.6 × 1018 e-

  • Coulomb’s law

    • charges should have absolute value around them

      • ε₀ (epsilon naught) is the permittivity of free space

        • 8.8 × 10-12

        • measure of how easily an electric field can be established in a vacuum

      • εr

        • permittivity of substance

  • μ0

    • permeability of free space = 4 pi * 10-7

  • What is a conductor/insulator

    • free electron gas is a conductor, free electrons can carry current

      • when you apply electrical field → free electron tends to move in a direction

    • insulator

      • no free electrons, tightly bound to atom

      • no current

  • semiconductor

    • in between conductors and insulators

  • EACH charged particle creates an electrical field

    • the source of an electrical field is a charged particle

  • The source of a magnetic field

    • is a moving charged particle (no movement, no magnetic field)

  • How to charge objects

    • induction

    • polarization

      • dipoles are formed (temporary charges)

    • friction

      • think rubbing a marker onto your head (electrons jump from head to marker, static)