Properties of cathode and anode rays

To explain the production and properties of cathode and anode rays. and also differentiate between two rays.

1. PROPERTIES OF CATHODE AND ANODE RAYS BY Ms.G.Kavitha ., Assistant Professor, PG & Research Department of Physics, Edayathangudy G.S Pillay Arts and Science college, Nagapattinam .

2. DISCOVERY OF ELECTRONS (CATHODE RAYS) Cathode rays  ( electron beam  or  e-beam ) are streams of  electrons  observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode (the electrode connected to the negative terminal of the voltage supply). They were first observed in 1869 by German physicist Julius Plücker  and Johann Wilhelm Hittorf , and were named in 1876 by  Eugen Goldstein Kathodenstrahlen , or cathode rays .  In 1897, British physicist  J.J . Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the  electron . Cathode-ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.

3. A gas discharge tube is fitted with two metallic electrodes acting as cathode and anode. The tube is filled with a gas ,air or vapours of substance at any desired pressure. The electrodes are connected to source of high voltage. The exact voltage required depends upon length of tube and pressure inside tube. The tube is attached to vacuum pump by means of small side tube so that conduction of electricity may be studied at any value of low pressure It is observed that current does not flow through gas at ordinary pressure even at high voltage of 5000 volts. When pressure inside tube is reduced and high voltage of 5000- 10000 volts is applied, then an electric discharge takes place through the gas pro ducing a uniform glow inside a tube. When pressure is reduced further to about 0.01 torr , the original glow disappears. Some rays are produced which create fluorescence on glass wall opposite to cathode . These rays are called cathode rays. The colour of glow or fluorescence produced on walls of glass tube, depends upon composition of glass.

4. PROPETIES OF CATHODE RAYS They travel linearly They have a negative electric charge They have particle property Magnets can deflect them Charge/mass ratio of the rays is constant They travel from the cathode to the anode Their properties are independent from the electrodes and gas present in the cathode ray tube. Cathode rays can ionize gas The travel more slowly than light They can heat objects that they hit They can penetrate through thin Aluminium plates They can make phosphors glow

5. An  anode ray  (also  positive ray  or  canal ray ) is a beam of positive ions that is created by certain types of gas-discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist  Eugen Goldstein, in 1886 .  Later work on anode rays by Wilhelm Wien and J. J. Thomson led to the development of mass spectrometry . If the cathode in a discharge tube is perforated, “luminous rays” are observed behind the cathode. These rays travel in a direction opposite to the cathode rays, i.e.., from the anode to cathode. These rays produce fluorescence when they strike a fluorescent screen present at the back of cathode. They are deflected by electric and magnetic fields. The direction of deflection indicates that they are positively charged. These rays are called Positive rays or Canal rays, DISCOVERY OF ANODE RAYS

6. These rays consists of positively charged ions produced by the ionization of the gas atoms by the fast moving electrons of the cathode rays. These positive ions travel towards the cathode and emerge out through the perforations in the cathode. The positive ions are gas atoms which have lost one or more electrons. Hence the mass of positive ion is almost the same as that of a neutral gas atom. “ PERFORATED CATHODE” Perforated cathode  means  cathode  with holes. In production of  anode  rays, a  perforated cathode  ray tube is used which is pierced with holes through which  anode  rays passed and form red spot behind the  cathode  because of strike between rays and wall of discharge tube.

7. They are travel in straight line. They can produce ionization in gases. These rays affect a photographic plate, produce fluorescence and penetrate thin aluminum foils. They are deflected by electric and magnetic fields. The direction of deflection indicates that they are positively charged. The magnitude of deflection suffered by positive rays is much smaller than that of cathode rays. Therefore, the positive ray particles are much heavier than the electrons. The velocities of all the positive ray particle is not the same. The velocities of these rays range from to   PROPETIES OF ANODE RAYS

8. ANALYSIS Millikan’s oil- drop experiment Thomson’s parabola method Aston’s spectrograph Dempster’s spectrograph Bainbridge’s mass spectrograph

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