X-rays are invisible electromagnetic radiations. Their wavelengths are smaller than those of the visible light. They are high-energy rays, have high penetrating power and travel at the speed of light. They can also pass through the flesh of human beings and animals. A German Scientist, Professor Wilhelm Conrad Roentgen in 1895, discovered x-rays. They are sometimes referred to as ‘Roentgen rays’ also. They were called x-rays (x means unknown) because not much was known about them earlier. Professor Roentgen was awarded the first Nobel Prize for Physics in 1901 for the discovery of x-rays. The apparatus used for producing x-rays is called ‘x-ray tube’. This tube is made up of hard glass and is fitted with two electrodes, which are connected to high voltage power supply. The electrode connected to the negative terminal is called cathode and the one connected to the positive terminal is called anode. Low pressure is created inside the tube by pumping out air from it. When high voltage is applied to the electrodes, electrons emerge from the cathode and strike the anode or the ‘target’, which produces x-rays. X-rays are very useful to us. They can pass through substances like wood, paper, skin and flesh but are absorbed by bones, iron, lead, etc. Doctors make use of x-rays to detect the dislocations and fractures of bones, examine the diseases of various organs and presence of stones in kidneys and gall bladder. The part of the body to be x-rayed is placed between the x-ray machine and the x-ray film. When the machine is switched on, the rays produce an image on the film, which is then developed like a negative. From the x-ray film, the areas affected by the disease or with defects are located easily. X-rays are also used to treat cancer. Airports use x-Rays on the baggage of the travellers because with the help of these rays, gold and other valuable gems as well as firearms hidden in the clothes can be detected easily. They are also used to detect cracks and bubbles in metals used for constructing bridges and building purposes. X-rays have a damaging effect on body’s cells, and it is for this reason that a person should not be exposed to x-rays quite often and for long durations. Today, using soft x-ray instruments like CAT (Computerised Axilliary Tomography) scanners are used to detect body abnormalities.