Physics
Physics
Problem
A vacuum chamber used for physics demonstrations is evacuated until the absolute pressure inside the chamber reaches . The chamber is located in a laboratory where the atmospheric pressure on that particular day is . (a) Determine the gauge pressure inside the chamber once the desired vacuum level has been reached. (b) A sensor mounted on the chamber door is designed to display pressure relative to the ambient laboratory air. What numerical reading (including the appropriate sign) should the sensor show under these conditions?Intuitive explanation
The key here is understanding gauge pressure versus absolute pressure. The chamber's interior is at 15 kPa absolute, but what matters for the net force pushing inward on the walls is the difference between outside and inside pressure. Think of it like a pressure imbalance: the atmosphere pushes in at 101 kPa while the weak vacuum inside pushes back at only 15 kPa, creating a net inward force. The gauge pressure—the "extra" pressure from the atmosphere—is what you'll use to find stresses on the chamber walls.
Intuitive explanation
The key here is understanding gauge pressure versus absolute pressure. The chamber's interior is at 15 kPa absolute, but what matters for the net force pushing inward on the walls is the difference between outside and inside pressure. Think of it like a pressure imbalance: the atmosphere pushes in at 101 kPa while the weak vacuum inside pushes back at only 15 kPa, creating a net inward force. The gauge pressure—the "extra" pressure from the atmosphere—is what you'll use to find stresses on the chamber walls.