Question

Vacuum pressure is usually measured using:

• A. Bourdon gauge
• B. U-tube manometer
• C. McLeod gauge
• D. Diaphragm gauge

Hint:

Logic Tip: The McLeod gauge solves the problem of "there is barely any gas here to measure" by trapping a huge sample of it and squishing it down until the pressure is actually high enough to see on a scale.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Standard pressure gauges often lack the sensitivity required to measure "vacuum" (pressures significantly lower than atmospheric pressure). Specialized instruments are used for these low-range measurements.
Step 2: Key Formula or Approach:
Identify the specialized vacuum measurement tool.
Step 3: Detailed Explanation:
The McLeod gauge is a scientific instrument used to measure very low pressures, down to $10^{-6}$ Torr. It works by taking a sample of the low-pressure gas and compressing it to a higher, measurable pressure using a column of mercury. Because it relies on Boyles' Law for its calibration, it is often used as a primary standard to calibrate other vacuum gauges.
Step 4: Final Answer:
Vacuum pressure is usually measured using a McLeod gauge.