Questions: Absolute, Gauge, and Atmospheric Pressure
2 questions to test your understanding
Score: 0 / 2
Question 1 Multiple Choice
A pressure gauge reads 250 kPa. Atmospheric pressure is 101 kPa. What is the absolute pressure?
A149 kPa
B250 kPa
C351 kPa
D101 kPa
Absolute pressure = gauge pressure + atmospheric pressure = 250 + 101 = 351 kPa. The gauge reads relative to atmosphere, so you must add atmospheric pressure to get the absolute value referenced to a perfect vacuum.
Question 2 Short Answer
A vacuum gauge reads 40 kPa. What is the absolute pressure if atmospheric pressure is 101 kPa?
Think about your answer, then reveal below.
Model answer: 61 kPa absolute. A vacuum gauge reads how far below atmospheric the pressure is, so P_abs = P_atm − P_vacuum = 101 − 40 = 61 kPa.
Vacuum readings are positive numbers representing negative gauge pressure. P_gauge = −40 kPa, so P_abs = 101 + (−40) = 61 kPa. This is above zero (no true vacuum), but low enough to risk cavitation if it approaches the vapor pressure of the liquid.