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Thursday, 9 March 2017

Dual Nature of Radiation and Matter - I


Electric Discharge:

The passage of an electric current through a gas is called electric discharge.

Discharge Tube:
A hard glass tube along with the necessary arrangement, which is used to study the passage of electric discharge through gases at low pressure, is called a discharge tube.

Cathode Rays:

Cathode rays are the stream of negatively charged particles, electrons which are shot out at a high speed from the cathode of a discharge tube at pressure below 0.01 mm of Hg.

Work Function:
The minimum amount of energy required by an electron to just escape from the metal surface is known as work function of the metal.
W0  = f0  = hv0
Electron Emission:
The minimum amount of energy required by an electron to just escape from the metal surface is known as work function of the metal.

Thermionic Emission:
Here electrons are emitted from the metal surface with the help of thermal energy.

Field or Cold Cathode Emission:
Electrons are emitted from a metal surface by subjecting it to a very high electric field.

Photoelectric Emission:
Electrons emitted from a metal surface with the help of suitable electromagnetic radiations.

Secondary Emission:
Electrons are ejected from a metal surface by striking over its fast moving electrons.

Forces Experienced by an Electron in Electric and Magnetic Fields:

a) Electric field: The force FE experienced by an electron e in an electric field of
strength (intensity) E is given by,
FE = eE


b) Magnetic field: The force experienced by an electron e in a magnetic field of strength B weber/m2 is given by
FE = eE


where v is the velocity with which the electron moves in the electric field and the magnetic field, perpendicular to the direction of motion.

c) If the magnetic field is parallel to the direction of motion of electron, then, FB = 0.

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