ANS:A - Mcloid

A pressure of 0.0001 absolute psi is extremely low and falls within the range typically measurable by a McLeod gauge.

Explanation:

• McLeod Gauge:
  • A McLeod gauge is a specialized instrument used to measure very low pressures, typically in the range of 10^-6 to 10^-3 absolute atmospheres, which corresponds roughly to 10^-4 to 10^-1 absolute psi.
  • It operates on the principle of compressing a known volume of gas and measuring the pressure change, allowing for highly sensitive pressure measurements.
• Other Gauges:
  • Pirani Gauge: A Pirani gauge measures pressures in the low to medium vacuum range (typically around 10^-3 to 10^3 Torr, or about 10^-3 to 10^3 mbar), but not as low as a McLeod gauge.
  • Thermocouple Gauge: Also known as a thermocouple vacuum gauge, it measures pressures from low to high vacuum (typically around 10^-3 to 10^-10 Torr), but is not suitable for measuring pressures as low as 0.0001 absolute psi.
• Conclusion:
  • Since a pressure of 0.0001 absolute psi is extremely low and falls within the sensitivity range of a McLeod gauge, it is the most appropriate instrument for measuring such low pressures. Therefore, the correct answer is McLeod gauge.