Find the frequency of the X-rays if their wavelength in vacuum is 20 pm.

In order to find the frequency of X-rays, if their wavelength in vacuum is 20 pm, we consider the equation for mechanical waves:

υ = λ ν.

That is, the speed of the wave is equal to the wavelength times the frequency.

For electromagnetic waves, and X-rays are such, the propagation speed is equal to c = 3 * 108 m / s (which is a constant value).

We can write the formula as:

c = λ ν.

v = c / λ.

Substitute the values and calculate:

v = 3 * 10 ^ 8/20 * 10 ^ -12 = 1.5 * 10 ^ 19 Hz = 15 EHz.