Diagram showing the workings of an X-ray machine. In an evacuated glass tube inside the machine, cathode filament is heated, releasing electrons from the filament surface. The positively-charged anode, a disc made of tungsten, attracts the electrons across the tube. The voltage difference is high, and the energetic electrons collide at speed with tungsten atoms in the anode, producing x-rays. X-rays are not absorbed very much by soft tissues and pass through them, but are absorbed by denser tissues such as bones, leaving shadows on X-ray film.