https://www.edumedia-sciences.com/es/

http://hyperphysics.phy-astr.gsu.edu/hbasees/hframe.html

https://drive.google.com/open?id=0BzQDb4ZMspdDUkhfOGZBMDdjbXM

http://www.geofisica.cl/uchile/universidad-de-chile/Electromagnetismo-Geofisica-TGT-NT2-Labs.htm