Cathode Rays: if
the gas pressure in a discharge tube is 10⁻² to 10⁻³ mm of Hg and a potential
difference of 10⁴ volt is applied between the electrodes, then a beam of
electrons emerges from the cathode which is called cathode rays. Hence cathode
rays are beam of high energy electrons Cathode is an electrode with a negative
charge.
Properties of cathode
rays:
(i)
Cathode rays are invisible and travel in
straight line.
(ii)
These rays carry negative charge and travel from
cathode to anode.
(iii)
These rays emerge perpendicular to the cathode
surface and are not affected by the position of anode.
(iv)
Cathode rays travel with very high velocity (1/
10th the velocity of light).
(v)
These rays are deflected by electric and
magnetic fields.
(vi)
These rays can ionize gases.
(vii)
These rays heat the material on which they fall.
(viii)
They can produce chemical change and thus affect
a photographic plate.
(ix)
These rays can penetrate through thin metal
foils.
(x)
The source of emf used in the production of
cathode rays is induction coil.
(xi)
When they strike a target of heavy metals such
as tungsten, they produce x-rays.
(xii)
The nature of cathode rays is independent of nature
of cathode and the gas in the discharge tube.
Positive or canal
rays:
If perforated cathode is used in a discharge tube, it is
observed that a new type of rays are produced from anode moving towards the
cathode and passed through the holes of cathode. These rays are positively charged
and are called positive rays or canal rays or anode rays. These rays were discovered
by Goldstein.
Properties of Canal
rays:
(i)
The positive rays consist of positively
charged particles.
(ii)
These rays travel in straight line.
(iii)
These rays can exert pressure and thus possess
kinetic energy.
(iv)
These rays are deflected by electric and magnetic
fields.
(v)
These rays are capable of producing physical
and chemical changes.
(vi)
These rays can produce ionization in gases.
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