BASICS OF UNITS — Identify the physical quantity. Question: The unit "bar" is used to measure which physical quantity?

Introduction / Context:
Everyday weather reports and many engineering tables use the unit “bar.” Recognizing what it measures helps connect meteorology, fluid mechanics, and instrumentation.

Given Data / Assumptions:

• “Bar” is a non-SI unit widely used for pressures around atmospheric levels.
• Standard atmospheric pressure at sea level is close to 1 bar.
• We are distinguishing among scalar thermodynamic and electrical quantities.

Concept / Approach:
Pressure equals force per unit area. SI uses the pascal (Pa). By definition, 1 bar = 10^5 Pa, which is very close to 1 atmosphere (1.01325 * 10^5 Pa). Hence bar is a convenient rounded unit for atmospheric and process pressures.

Step-by-Step Solution:
Recall: 1 bar = 100,000 Pa.Atmospheric pressure at sea level ≈ 1.01325 bar.Therefore, “bar” measures pressure, often atmospheric or gauge pressures.Options linked to temperature, heat, current, or resistance are unrelated dimensions.

Verification / Alternative check:
Instrument dials on compressors or scuba gear often show pressure in bar alongside psi or kPa, reinforcing the interpretation.

Why Other Options Are Wrong:
A) Temperature is in K, °C, or °F.B) Heat is energy, measured in J or cal.D) Current is in ampere (A).E) Resistance is in ohm (Ω).

Common Pitfalls:
Confusing “bar” (pressure) with “bar” as a length of metal (shape), or mixing up atmospheric “atm” and “bar.” Remember the simple relation 1 bar = 10^5 Pa.

Final Answer:
atmospheric pressure