Question

Pirani gauge operation is based on the following principle:

• A. Change in volume with pressure
• B. Change in viscosity with pressure
• C. Change in thermal conductivity of gas with pressure
• D. Ionization of gas at low pressure

Hint:

Pirani gauge → used for vacuum measurement → based on heat conduction by gases.

Answer 1

The Correct Option is C

Pirani gauges are commonly used in instrumentation engineering to measure low pressures, typically in vacuum systems. They operate based on the principle that the thermal conductivity of a gas changes with pressure. Here's how it works:

• The gauge contains a heated filament that loses heat to the surrounding gas. The rate of heat loss depends on the thermal conductivity of the gas.
• As pressure changes, the density of the gas also changes, leading to a variation in thermal conductivity.
• The change in thermal conductivity alters the heat loss from the filament, causing a change in its temperature.
• This temperature variation impacts the filament's electrical resistance, which is measured to determine the pressure of the gas.

The correct answer for the principle of Pirani gauge operation is: Change in thermal conductivity of gas with pressure.