Practice portal › Dual Nature of Matter and Radiation › Electron Emission and Cathode Rays
Asked in AIPMT 2006 · Discharge through gases
The field in a discharge tube accelerates free electrons much more effectively than ions, because an electron is thousands of times lighter and reaches a high speed over the same distance.
At low pressure an electron travels far between collisions, so it gains a large kinetic energy before it strikes anything.
When it hits a neutral atom with more than the ionisation energy, it knocks out another electron.
That freed electron is accelerated in turn, and the process cascades, which is what sustains the discharge.
So the ionisation comes from collisions between negative electrons and neutral atoms or molecules.
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