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ag CATHODE RA’
ELECTRON
d existence of electron was establisheg
duction of electricity through gases, In 18
d the study of conduction of elect
pressure in a discharge tube. [A ¢ "
ts of a hard glass cylindrical tube (
tal electrodes sealed on both the ends, Iti
connected to a side tube through which it can be evacuated to
desired pressure with the help of a vacuum pump.] Air was al
completely removed from the discharge tube (pressure about 104
atmosphere). When a high voltage of the order of 10,000 volts g
more was impressed across the electrodes, some sort of invisib
rays moved from the negative electrode to the positive electr
(Fig. 2.1). Since, the negative electrode is referred to as cathode,
The nature an
experiments on con
Julius Plucker starte
through gases at low
discharge tube consist
50 cm long) with two met
Gas at low pressure
Cathode
Cathode rays
Vacuum pump
Fig. 2.1 Production of cathode rays
these rays were called cathode rays. Further investigations wee
made by W. Crookes, J. Perrin, J.J. Thomson and others. Cathode
rays possess the following properties:
(i) They travel in straight lines away from the cathod
very high velocities ranging from 10° —10!! cm per secon?
shadow of metallic object placed in the path is cast on the val
opposite to the cathode.
(ii) They produce a green glow when strike the glass wal
beyond the anode. Light is emitted when they strike the "
sulphide screen.
i (ii) The produce heat energy when they collide with i
maeoten: iv titzt cathode rays possess kinetic enerey whe
cor.verted into neat energy when stopped by matter.
fe with (iv) 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.
They discharge a positively charged gold leaf electroscope. It
shows that cathode rays carry negative charge.
(v), They possess kinetic energy. It is shown by the
experiment that when a small pin wheel is 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.
These particles carrying negative charge were called negatrons
oy Thomson.
The name ‘negatron’ was changed to ‘electron’ by Stoney.
(vi) Cathode rays produce X-rays. When these rays fall on a
material having high atomic mass, new type of penetrating rays
of very small wavelength are emitted which are called X-rays.
(vii) These rays affect the photographic plate.
(viii) These rays can penetrate through thin foils of solid
materials and cause ionisation in gases through which they pass.
(ix) The nature of the cathode rays is independent of :
(a) the nature of the cathode and
(b) the gas in the discharge tube.
