In 1895 German scientist prof. Rontgen observed that when fast moving cathode rays strike a metal piece of high atomic weight and high melting point, a new kind of rays are produced known as X-rays. The intensity of X- rays is proportional to the number of electrons emitted per second from the filament. If the number of electrons striking the target is increased, the quantity of X-rays produced will also be increased, that is, high-intensity X-rays will be produced. Therefore, in order to 'Increase the intensity of the X-rays produced in a Coolidge tube, the current through its filament is increased. This increases the number of electrons emitted by the filament and hence, the intensity of X-rays produced is increased.