June 9, 2008

A global gauge transformation has the same phase shift everywhere whereas a local gauge transformation has a phase shift as a function of location.

Benjamin Franklin fixed the convention for positive and negative charge and the direction of current flow.

Lorentz invariance of the equation of motion implies that the Lagrangian must be a scalar. Gauge invariance of the Lagrangian implies conservation of charge.

The Lorentz force is the force of the electromagnetic field upon a charge.

No magnetic monopoles have been observed although some theories allow for them. A field approximating a magnetic monopole can be constructed using a very long solenoid. 

Topics: 
  • Gauge transformation
  • Gauge invariance
  • Conservation of charge
  • Lorentz force
  • Magnetic monopoles