Definitions of Pressure — Comparing to Atmosphere When the pressure intensity at a point is greater than the local atmospheric pressure, the difference between them is called:
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Agauge pressure
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Babsolute pressure
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Cpositive gauge pressure
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Dvacuum pressure
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E—
Answer
Correct Answer: gauge pressure
Explanation
Introduction:Engineering pressure terms distinguish between measurements relative to absolute zero and measurements relative to the local atmosphere. Correct terminology avoids confusion in design and safety calculations.
Given Data / Assumptions:
- Local atmospheric pressure p_atm is the reference for many instruments.
- Measured pressure p is greater than p_atm.
Concept / Approach:Absolute pressure p_abs is measured from absolute vacuum. Gauge pressure p_g is measured relative to p_atm. If p > p_atm, then p_g = p - p_atm is positive and is called gauge pressure (often implicitly positive). Vacuum pressure typically refers to p_atm - p when p < p_atm.
Step-by-Step Solution:Compute p_g = p - p_atm.Given p > p_atm, p_g > 0, named gauge pressure.Absolute pressure would be p_abs, not the difference; vacuum pressure applies when p < p_atm.
Verification / Alternative check:Typical pressure gauges read zero at atmosphere. A reading of 200 kPa on a gauge implies 200 kPa gauge, not absolute; absolute would be approximately 200 + 101.3 ≈ 301.3 kPa (assuming standard atmosphere).
Why Other Options Are Wrong:Absolute pressure: not a difference; it includes atmospheric baseline.Positive gauge pressure: a descriptive phrase, but the precise term is simply gauge pressure.Vacuum pressure: used when pressure is below atmospheric (negative gauge).
Common Pitfalls:Confusing gauge and absolute scales; mixing units; forgetting local altitude and weather change p_atm slightly.
Final Answer:gauge pressure