Question

Which of the following gauges can measure the lowest vaccum pressure ?

• A. McLeod gauge
• B. Pirani gauge
• C. lonisation gauge
• D. Thermocouple gauge

Answer 1

The correct option is C lonisation gauge

Pirani gauge $\to$ upto ${10}^{-4}$ Torr
Mcleod gauge $\to$ upto ${10}^{-6}$ Torr
lonisation vaccum gauge $\to$ upto ${10}^{-9}$ Torr

So, lonisation vaccum gauge can measure lowest vaccum preassure.

Note: vaccum pressure is pressure having a value below atmospheric pressure.