Electric Field

Summary

• Field
  • A field is…
    • a physical quantity that has a value (or set of values) at every point in space and time
    • a mathematical function that returns a value (or set of values) for every point in space and time
    • a way to deal with philosophical arguments against action at a distance
  • Fields can be…
    • scalar fields associated with quantities such as…
      • temperature
      • pressure
      • density
      • electric charge
    • vector fields associated with…
      • the flow of fluids (the velocity field) such as…
        • wind
        • ocean currents
        • solar wind
      • non-contact forces (force fields) such as…
        • gravitational field
        • electric field
        • magnetic field
    • tensor fields associated with…
      • continuum mechanics quantities, namely the…
        • stress tensor
      • general relativity quantities such as the…
        • metric tensor
        • stress-energy tensor
        • Ricci curvature tensor
• Electric field
  • Magnitude

    E =	FE
    	q

    Where…

    E =	magnitude of electric field (electric field strength)
    Fg =	electric force on test charge
    q =	charge of test charge

  • The electric field has two frequently used, equivalent SI units…
    • the newton per coulomb and
    • the volt per meter.

    ⎡ ⎢ ⎣	N	=	V	⎤ ⎥ ⎦
    	C		m

  • Direction
    • Electricity is described by a vector field.
    • The direction of the electric field at any point in space is the direction of the net electric force on a "small" positive test charge.
    • Use vector addition to find the net electric field when more than one charged object is present.
  • Diagrams
    • The electric field around a spherically symmetric charge is radial and…
      • diverges from positive charge
      • converges on negative charge
    • Field lines never intersect.
    • Electric field strength is proportional to line density.