Questions on Compressibility
Compressibility – Multiple Choice Questions
1. What is compressibility?
A) The ability of a fluid to flow
B) The resistance of a fluid to shear stress
C) The measure of the change in volume under pressure
D) The tendency of solids to expand when heated
E) The ability of gases to mix freely
2. Which of the following substances is generally considered highly compressible?
A) Water
B) Steel
C) Mercury
D) Air
E) Glass
3. What is the unit of compressibility in the SI system?
A) m²/s
B) 1/Pa
C) N/m²
D) Pa·s
E) kg/m³
4. The mathematical expression for compressibility (κ) is:
A) κ = ΔV / ΔP
B) κ = ΔP / ΔV
C) κ = - (1/V) × (∂V/∂P)
D) κ = V × P
E) κ = P × T / V
5. If a substance has low compressibility, it means:
A) It expands significantly under pressure
B) Its volume increases with increased pressure
C) It has a high rate of heat conduction
D) Its volume changes very little under pressure
E) It has a high density
6. For gases, compressibility becomes more significant at:
A) Low temperatures and high pressures
B) High temperatures and low pressures
C) Standard atmospheric conditions
D) Zero gravity
E) Room temperature
7. What type of process assumes zero compressibility?
A) Adiabatic
B) Isobaric
C) Incompressible
D) Isothermal
E) Isochoric
8. Which of the following materials is typically considered incompressible in fluid dynamics?
A) Helium
B) Water
C) Methane
D) Steam
E) Air
9. The compressibility factor (Z) is used in:
A) Newton's law of viscosity
B) Ideal gas law adjustments
C) Bernoulli’s equation
D) Fluid statics
E) Thermocouples
10. When is Z (compressibility factor) equal to 1?
A) For real gases under high pressure
B) For all liquids
C) For ideal gases
D) For solids at melting point
E) For gases at absolute zero
11. The bulk modulus (K) is related to compressibility how?
A) K = 1/κ
B) K = κ × P
C) K = V × κ
D) K = T × κ
E) K = κ²
12. If the bulk modulus of a material is very high, the material is:
A) Easily compressible
B) Thermally unstable
C) Rigid and resistant to compression
D) Very elastic
E) Electrically conductive
13. In atmospheric science, compressibility explains:
A) Ocean salinity variation
B) Temperature inversion
C) Air pressure and density changes with altitude
D) Lightning formation
E) Magnetic field alignment
14. Which of the following would not significantly affect gas compressibility?
A) Pressure
B) Temperature
C) Volume
D) Gas constant
E) Chemical composition
15. The compressibility of a substance influences:
A) The color of light it reflects
B) Its magnetic susceptibility
C) Its behavior under mechanical stress
D) Its refractive index
E) Its entropy
16. What happens to compressibility when temperature increases (generally)?
A) It decreases in gases
B) It increases in gases
C) It becomes zero
D) It becomes negative
E) It does not change
17. Which of the following best describes the compressibility of liquids?
A) Liquids are as compressible as gases
B) Liquids are completely incompressible
C) Liquids are less compressible than gases
D) Liquids compress more with temperature
E) Liquids expand under pressure
18. What does a compressibility factor Z < 1 indicate for a real gas?
A) The gas behaves ideally
B) The gas is more compressible than expected
C) The gas volume is greater than ideal
D) The temperature is too high
E) The gas has zero entropy
19. In which field is understanding compressibility least important?
A) Aerodynamics
B) Hydraulic engineering
C) Thermodynamics
D) Optical fiber design
E) Meteorology
20. In computational fluid dynamics (CFD), compressible flow simulations are necessary when:
A) Fluid velocity is low
B) Fluid is water
C) Mach number exceeds 0.3
D) Temperature is constant
E) Flow is laminar
Answers with Explanations
1. C – Compressibility is the measure of volume change under pressure.
2. D – Gases like air are highly compressible.
3. B – Compressibility has units of inverse pressure (1/Pa).
4. C – Standard definition from thermodynamics.
5. D – Low compressibility means small volume change.
6. A – Gases deviate from ideal behavior under these conditions.
7. C – Incompressible processes assume no volume change.
8. B – Water is often treated as incompressible in fluid dynamics.
9. B – Z accounts for deviations in real gases from ideal gas law.
10. C – Ideal gases have Z = 1.
11. A – Bulk modulus is the inverse of compressibility.
12. C – High K means strong resistance to compression.
13. C – Compressibility explains how pressure and density vary with height.
14. D – The gas constant (R) is constant and does not vary with the gas.
15. C – Compressibility is directly linked to mechanical properties.
16. B – For most gases, compressibility increases with temperature.
17. C – Liquids are much less compressible than gases.
18. B – Z < 1 means the gas is more compressible than predicted.
19. D – Optical fibers are more concerned with light transmission.
20. C – Mach number > 0.3 requires compressible flow modeling.
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