The conductivity of gasses at low pressure can be termed as
- I. Hot cathode emission
- II. Thermionic emission
- III. Cold cathode emission
- IV. Field emission
- A. I & II
- B. II & III
- C. III & IV
- D. IV & I
Let’s analyze each statement as follows:
- Hot cathode emission is the liberation of streams of electrons from a metal surface by subjecting it to intense heat. It is not the same as gas conductivity at low pressure.
- Thermionic emission basically means the same thing as hot cathode emission. Thermionic emission is the liberation of electrons from a metal surface by subjecting same to heat. This is different in concept from gas conductivity at low pressure.
- Cold cathode emission is the liberation of electrons when high voltage is applied to a low-pressure gas. Heat is not involved here.
- Field emission is the emission of electrons when a conductor is subjected to a strong electric field. This is basically what happens when gasses at low pressure is subjected to high potential difference.
I believe it is now obvious that III and IV are correct.
Now for the right answer to the above question:
- Option A is incorrect. in gas conduction at low pressure, electrons are liberated by high voltage and not by heat.
- Option B is incorrect.
- C is correct. during cold cathode emission, low pressure gasses are subjected to strong electric field.
- D is not the correct answer.
You may please note these/this:
- Thermionic emission and hot-cathode emission simply mean the same thing, they are different names describing almost the same thing.
- Field emission, cold-cathode emission, and low pressure gas conductivity all mean the same thing.
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/ culled from 2019 JAMB-UTME physics question 32 /