Soft X-rays and Hard X-rays
X-rays are of two types : (i) Soft X-rays and (ii) Hard X-rays
(i) Soft X-rays
X-rays having wavelength of 4Å or above, have lesser frequency and hence lesser energy. They are called soft X - rays due to their low penetrating power. They are produced at comparatively low potential difference.
(ii) Hard X-rays
X-rays having low wavelength of the order of 1Å have high frequency and hence high energy. Their penetrating power is high, therefore they are called hard X-rays. They are produced at comparatively high potential difference.
The wavelength of X-rays depends upon the kinetic energy of the electrons producing them and this kinetic energy depends upon the potential difference between the filament and the target.
A German scientist, Wilhelm Roentgen, in 1895, discovered X-rays when he was studying the phenomenon of discharge of electricity through gases.
After performing a series of experiments, Roentgen concluded that when a beam of fast moving electrons strike a solid target, an invisible penetrating radiation is produced. Due to the unknown nature of the radiation, Roentgen called these radiations as X - rays.
X-rays are electromagnetic waves of short wavelength in the range of 0.5 Å to 10 Å. Roentgen was awarded Nobel prize in 1901 for the discovery of X-rays.