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.
4. • 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 producing 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.
5. 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
6. • 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
7. • 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.
8. • 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 105 to 106 𝑚𝑠−1.
PROPETIES OF ANODE RAYS
