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Discharge Through Gases and Atomic Excitation
Concepts tested here
- Origin of glow in a discharge tube
All Questions
2008 AIPMT 1 question
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In the phenomenon of electric discharge through gases at low pressure, the coloured glow in the tube appears as a result of -In a discharge tube at low pressure, the charged particles (electrons) emitted from the cathode are accelerated by the applied electric field.
These fast particles collide with the atoms of the gas present in the tube.
In such a collision, energy is transferred to the atom and its electrons are raised from the ground state to higher (excited) energy levels.
The excited state is unstable, so the electrons quickly fall back to lower energy levels.
During each downward transition a photon of definite energy $h\nu = E_2 - E_1$ is emitted, which is seen as light of a definite colour.
Since the energy levels are characteristic of each gas, every gas gives its own colour of glow (for example, neon gives an orange-red glow).
Thus the coloured glow appears as a result of the excitation of the electrons in the atoms of the gas, produced by the collisions of the cathode particles with the gas atoms.