What properties of a wave do you need to calculate the wave speed?

The frequency and the wavelength

Explanation:

A wave is a periodic disturbance of the space that carries energy without carrying matter.

The displacement of a wave is described by a sine/cosine function.

Moreover, there exist two types of waves:

- Mechanical waves: they are produced by the oscillations of the particles in a medium - they can only propagate through a medium (not through a vacuum)

- Electromagnetic waves: they consist of the oscillations of the electric and magnetic fields - these are the only waves able to propagate through a vacuum

The speed of a wave is given by:

where:

is the frequency of the wave, which is the number of oscillations completed by the wave per second

is the wavelength of the wave, which is the distance between two consecutive crests (point of maximum amplitude) of the wave

Therefore, if we know wavelength and frequency of a wave, we can calculate its speed.

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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