EM WAVE V EM WAVELENGTH

Light is an electromagnetic wave: it is a ripple through both the electric field and the magnetic field simultaneously. These two fields exist perpendicular to each other, so a wave through them is represented as two sine waves at right angles to each other.

The wavelength is measured from the peak of one wave to the peak of the next, or the trough of one to the trough of the next. This is different to amplitude, which is the height of the wave from trough to peak.