Concept:In a discharge tube, ionization occurs through collisions between high-energy electrons and neutral gas atoms/molecules.
Explanation:1.
Setup in discharge tube: A high voltage is applied across two electrodes in an enclosed gas at low pressure.
2.
Initial ionization: The electric field accelerates free electrons (from residual ionization) toward the anode, gaining high kinetic energy.
3.
Collision mechanism: These high-energy electrons collide with neutral gas atoms/molecules.
4.
Ionization process: When a fast electron collides with a neutral atom/molecule, it can knock out an electron from the atom, creating:
- A positive ion (atom minus an electron)
- A secondary electron (the knocked-out electron)
5.
Cascade effect: These secondary electrons are also accelerated and cause further collisions, leading to impact ionization and a discharge.
6.
Why other options fail:- Option A: Neutral atoms alone don't ionize each other
- Option B: Positive ions move toward cathode and don't cause primary ionization
- Option D: Photons are produced *after* ionization, not the cause
Answer:C. negative electrons and neutral atoms/moleculesThe ionization in a discharge tube is primarily produced by collisions between
high-energy electrons and neutral gas atoms/molecules through the process of impact ionization.
