The discovery of electromagnetic waves. The lesson may be started with a discussion of waves. It isn't completely accurate, but it covers the waves studied here. Ripples forming on the surface of water, after a stone is thrown in. Sound waves, in air, water and solid materials.
Earthquakes propagate as waves in the solid earth.
These can be viewed as one-dimensional waves, spreading along a given direction only. Radio Waves . So are electrons and ions. Unless raised by a student, the following is better skipped, to save time and potential confusion. Wave velocity v , the velocity with which crests advance in space.