Pressure Measurement — Manometer Capability Can a manometer be configured to measure vacuum (negative gauge) pressures as well as positive gauge pressures?
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AAgree
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BDisagree
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C—
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D—
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E—
Answer
Correct Answer: Agree
Explanation
Introduction / Context: Manometers are fundamental devices for measuring pressure differences using hydrostatic columns. With appropriate connection and reference, they can indicate pressures above or below atmospheric pressure (gauge positive or vacuum/negative gauge).
Given Data / Assumptions:
- U-tube or inclined manometer with a suitable manometric fluid (e.g., mercury, water, oil).
- One leg can be open to atmosphere; the other connected to the system point.
- Hydrostatic equilibrium applies, neglecting capillary corrections at macroscales.
Concept / Approach: The manometer measures pressure difference via Δp = ρ_m g Δh (adjusted for fluid columns). If the system pressure is below atmospheric, the meniscus moves opposite to the positive case, and the indicated height difference corresponds to a vacuum (negative gauge) value. Thus, by reading Δh and sign, vacuum is readily measured.
Step-by-Step Reasoning:
Connect one limb to the point of interest and the other to atmosphere. If p_system < p_atm, the column shifts to show a deficit; compute |p_atm − p_system| = ρ_m g Δh (with corrections if multiple fluids are present). Report vacuum magnitude and, if needed, convert to absolute pressure p_abs = p_atm − |p_vac|.Verification / Alternative check: Industrial vacuum lines routinely use mercury or oil manometers and Bourdon gauges scaled for negative gauge pressure, confirming practicality.
Why Other Options Are Wrong: “Disagree” ignores common practice and the symmetric operation of manometers around atmospheric reference.
Common Pitfalls: Misreading sign conventions; using an inappropriate manometric fluid (too light or hazardous); neglecting capillary or temperature corrections in precise work.
Final Answer: Agree — manometers measure both vacuum and positive gauge pressures.