Does the equation for calculating the speed of a wave not apply to light waves?

Answer 1

There are several equations relating the speed of a wave to other parameters. Let us call the speed of a wave v. The following equations are true for ALL waves, including (but not limited to) sound waves, water waves, electromagnetic (light) waves, and waves on a string like on a guitar:

v = l * f

Here l is the wavelength of the wave and f is the frequency. Imagine a bunch of ripples of water, or the graph of the function sin(x). The distance between two peaks in these cases is the wavelength. The frequency of a wave is the number of wavelengths created per unit time. Another equation which describes the speed of a wave is called, appropriately, the wave equation. This equation is a differential equation, which means that it relates a function F to a "rate of change" of itself. For example, the speed of an object is the rate of change in the object's position. See the Wikipedia article describing the wave equation.

Now light waves are special kinds of waves because they are the only kind of wave that can propagate through empty space (ignoring quantum mechanical waves). In empty space (vacuum), light ALWAYS travels at the speed of light (really?!), or 180,000 miles per second. This is not true for other kinds of waves (sound waves need to propagate through matter like air or metal, water waves need to propagate through water [SURPRISE], and it doesn't take a genius to realize that waves on guitar strings actually need the strings in order to exist).