Physics 201- Introduction to Electricity & Magnetism
November 13-  Ampere's Law






  Gauss' Law and Magnetism

What is the net magnetic flux through any closed surface?

Ampere's Law

Be careful with your direction of integration.

Ampere's Law is useful, when there is symmetry.

  • What does symmetry mean here?  When we were working with Gauss' Law and electric fields, we needed the electric field to be either perpendicular or parallel to the normal of our surface.  This made the flux integral easy as the flux became EA or 0, there were no integrals to perform. 
  • For magnetic fields and Ampere's Law symmetry means that the magnetic field is either parallel or perpendicular to the path of integration.  This way the sum of B along the path is either Bl or 0. 
  • Just like Gauss' Law, Ampereís Law is always true, it just isn't useful unless we have this symmetry. 


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Jeff Phillips
Loyola Marymount University
Fall 2002