Wavelength and frequency

To picture electromagnet waves think of ocean waves, or ripples in a pond. The wavelength of any wave is the distance from the top of one wave or ripple to the top of the next one. It's sometimes called the ``peak to peak'' distance. The frequency is the number of times a wave top appears, per second, at one place. Wavelengths are measured using any convenient unit of length, but frequencies (of light) are almost always specified in ``cyles per second,'' which is often abbreviated 'Hertz' or 'Hz.'