Electromagnetic radiation (ER) is a form of energy, and it acts like a wave as it moves at the speed of light--it's how energy from the sun reaches Earth. ER is classified by frequency--how many times the wave oscillates in a given amount of time.

Originally released by National Science Foundation, 2011. Streaming video file encoded with permission for digital streaming by Infobase on May 05, 2015.

Electromagnetic Radiation: Chalk Talk (1:00); .