Using x-rays to peer into the human body was a major milestone in modern medicine. Wilhelm Röntgen (German ,1845-1923)
discovered the portion of the electromagnetic spectrum that he called “x-rays”. X-ray wavelengths range from 0.1 to 10 Angstroms compared to 4000 to 7000 Angstroms for visible light.
In its simplest form, the wave equation refers to a scalar quantity u that satisfies
is a fixed constant equal to the propagation speed of the wave.