Question

What is the frequency of an x-ray with wavelength 0.15 nm ? assume that the wave travels in free space?

Answer 1

Let's convert first the wavelength into meters:
$\lambda = 0.15 nm = 0.15 \cdot 10^{-9}m$
Then, we know that the wavelength is related to the frequency by the following equation:
$f = \frac{c}{\lambda}$
Where $c=3 \cdot 10^8 m/s$ is the speed of light in free space. Therefore, putting in the numbers, we find the frequency f:
$f= \frac{3 \cdot 10^8 m/s}{0.15 \cdot 10^{-9}m}=2 \cdot 10^{18}Hz$