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Discharge Through Gases
Concepts tested here
- Ionisation by electron collision
All Questions
2006 AIPMT-PRE 1 question
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In a discharge tube ionization of enclosed gas is produced due to collisions between :A gas at low pressure in a discharge tube always contains a few free electrons and ions (produced by cosmic rays and natural radioactivity).
When a high potential difference is applied, these free electrons are accelerated towards the anode.
Because the pressure is low, the mean free path is long, so the electrons gain enough kinetic energy between collisions.
When such a fast electron collides with a neutral atom or molecule of the gas, it knocks out an electron and ionises it.
The electrons released are in turn accelerated and ionise more atoms, so the ionisation multiplies.
Electrons are much lighter and faster than positive ions, so they are far more effective in producing ionisation.
So the ionisation is produced due to collisions between negative electrons and neutral atoms/molecules.