Atomic Structure : Discovery of electron (CATHODE RAYS)

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Discovery of electron (CATHODE RAYS)

In 1859, Julius plucker started the study of conduction of electricity through gases at low pressure in a discharge tube. When a high voltage of the order 10,000 volts or more was impressed across the electrodes, some sort of invisible rays moved from the –ve electrode to the +ve electrode. Since the –ve electrode is referred to as cathode, these rays were called cathode rays.

Properties of Cathode rays

•  They travel in straight lines away from cathode with very high velocity .
•  A shadow of metallic object placed in the path is cast on the wall opposite to the  cathode.

•  They produce a green glow when strick the glass wall matter. Light is emitted when they strike the zinc-sulphide screen(fluorescent material).
• When a small pin wheel  placed in their path, the blades of the wheel are set in motion. Thus the cathode rays consist of material particles which have mass and velocity.

• They are deflected by the electric and magnetic fields. When the rays are passed between two electrically charged plates, these are deflected towards the positively charged plate. It shows that cathode rays carry -ve charge. These particles carrying negative charge were called negatrons by Thomson. The name negatron was changed to 'electron' by Stoney.

• They produce heat energy when they collide with the matter. It shows that cathode rays posses Kinetic energy which is converted into heat energy when stopped by matter.  
• Cathode rays can ionize the gases through which they pass.
•  Cathode rays can penetrate the thin foil of solid materials.
• These rays affect the photographic plate.
• The nature of cathode rays is independent of

(a) The nature of cathode and

(b) The gas in discharge tube.

Hope you understand discovery of electron 

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