NASA
Nasa: Magnetic Fields
This site from NASA provides a short, illustrated description of the basics of magnetic fields and magnetic poles.
Michigan State University
Michigan State University: Physics: Electric Fields and Potentials
Defines electric potential, field lines, and equipotential lines. Contains example problems and formulas for solving.
Texas Education Agency
Texas Gateway: Electric and Magnetic Forces
Given diagrams, illustrations, or descriptions, students will identify examples of electric and magnetic forces.
CK-12 Foundation
Ck 12: Physical Science: Using Earth's Magnetic Field
[Free Registration/Login may be required to access all resource tools.] The Earth's magnetic field and how it protects life on Earth, and how it is used for navigation.
CK-12 Foundation
Ck 12: Physical Science: Magnetic Field Reversal
[Free Registration/Login may be required to access all resource tools.] Discusses what a magnetic field reversal is and the evidence that this has happened with the Earth.