Question

The ionization gauge is an instrument used for the measurement of

• A. Vacuum pressure
• B. Medium pressure
• C. High pressure
• D. Very high pressure

Hint:

Ionization gauges are the gold standard for measuring ultra-high vacuums down to $10^{-12}\text{ Torr}$.
They cannot operate at atmospheric pressure as the filament would oxidize and burn out immediately.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the pressure range or application for which an ionization gauge is used.

Step 2: Detailed Explanation:

• An ionization gauge is a highly sensitive pressure measuring instrument designed to measure extremely low gas pressures, typically in the high-vacuum to ultra-high-vacuum range ($10^{-3}\text{ Torr}$ to $10^{-12}\text{ Torr}$).

• It works by using electrons (emitted from a hot filament or cold cathode) to ionize the residual gas molecules inside the gauge volume.

• These positive ions are attracted to a collector electrode, creating an ion current.

• The magnitude of this ion current is directly proportional to the number density of the gas molecules, which corresponds to the pressure.

• At higher pressures (such as atmospheric or medium pressures), the high density of gas molecules leads to rapid filament burnout and excessive ion currents, making the ionization gauge unsuitable.

• Therefore, it is specifically designed and used for measuring vacuum pressure.

Step 3: Final Answer:
The ionization gauge is used for the measurement of vacuum pressure.