MCQ Detailed View

Viscosity is the measure of a fluid’s resistance to flow. It describes how much a fluid resists movement when a force is applied. In liquids, it results from internal friction caused by intermolecular forces. Viscosity is an important concept in physical chemistry and fluid dynamics.

The standard unit of dynamic viscosity in the CGS (centimeter-gram-second) system is the poise. It is named after Jean Léonard Marie Poiseuille, a French physicist. One poise (P) is defined as one dyne-second per square centimeter (dyne·s/cm²). In SI units, viscosity is measured in Pascal-seconds (Pa·s), where 1 Pa·s = 10 poise.

Viscosity is often expressed in centipoise (cP), where 1 poise = 100 centipoise. For example, water at 20°C has a viscosity of about 1 cP.

Each of the other options listed belongs to different physical quantities:

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  Decibel is a unit used to measure sound intensity or loudness.

  
  


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  Torr is a unit of pressure. One torr is approximately equal to 1/760 of atmospheric pressure.

  
  


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  Hertz (Hz) is a unit of frequency, indicating cycles per second.

  
  

Only poise is used to measure viscosity. It specifically applies to dynamic viscosity. Another related property is kinematic viscosity, which is measured in stokes (St) in the CGS system and m²/s in the SI system. Kinematic viscosity is the ratio of dynamic viscosity to density.

Knowing the correct unit is important for interpreting data in physics, engineering, and chemistry, especially when working with fluids in processes like lubrication, flow control, and material design.