Pressure terminology: a pressure value less than atmospheric pressure is referred to as

Introduction / Context:
Engineers use different reference frames for pressure: absolute, atmospheric, and gauge. Values below atmospheric occur in condensers, primed pump suctions, and vacuum systems, and are described by several equivalent terms in practice.

Given Data / Assumptions:

• Atmospheric pressure p_atm as the reference for gauge readings.
• Gauge pressure p_gauge = p_absolute − p_atm.
• Negative gauge indicates p_absolute < p_atm.

Concept / Approach:

When p_absolute is less than atmospheric, p_gauge becomes negative. This condition is commonly described as “vacuum pressure,” “negative gauge pressure,” or colloquially as “suction,” acknowledging that devices do not pull fluids but create a pressure differential that ambient pressure uses to push fluids in.

Step-by-Step Solution:

Verification / Alternative check:

Vacuum gauges read in mmHg or kPa below atmospheric; converting these to gauge pressure yields negative values, confirming equivalence of terms.

Why Other Options Are Wrong:

(e) Absolute pressure is referenced to zero vacuum and is never negative; it cannot describe a state “less than atmospheric” without specifying the reference.

Common Pitfalls:

Assuming suction is a force; it is merely lower pressure. Confusing absolute and gauge scales when sizing equipment or interpreting specifications.

Final Answer:

All the above