Problem 60 - A Complete Resource Book in Chemistry for JEE Main

Question

Poise is a unit of (a) viscosity (b) vapour pressure (c) surface tension (d) parachore value

Step-by-Step Solution

Answer

(a) viscosity.

Step 1: Understand the Question

The question asks us to identify the physical property that is measured in poise. We need to recall the definitions or unit associations for each of the given options: viscosity, vapor pressure, surface tension, and parachore value.

Step 2: Recall the Definition of Poise

Poise is a unit for measuring viscosity. The poise is a centimeter-gram-second (CGS) unit of dynamic viscosity, named after Jean Léonard Marie Poiseuille. It is commonly used in physics to describe the measure of a fluid's resistance to gradual deformation by shear stress or tensile stress.

Step 3: Analyze the Options

Now that we understand poise measures viscosity, examine all options. Option (a) is viscosity, which aligns with the definition of poise. Vapor pressure, surface tension, and parachore value do not measure in poise.

Step 4: Select the Correct Answer

Based on our understanding, the correct choice is that poise is a unit for measuring viscosity, which matches option (a).

Step 5: Verify and Confirm the Answer

Verify your understanding by reviewing the physical property definitions. Since viscosity is the only property related to poise, we confirm the answer as (a) viscosity.

Key Concepts

Units of Measurement

Units of measurement allow us to quantify and compare different physical properties. In the field of physics, these units are crucial to understanding the nature and behavior of materials and phenomena. For example, when we talk about viscosity, it's important to have a standard unit to describe how thick or thin a fluid is.
In the metric system, the centi-meter-gram-second (CGS) system is one of the commonly used systems, particularly in older texts and specific domains like fluid dynamics.

• Length is measured in centimeters (cm)
• Mass is measured in grams (g)
• Time is measured in seconds (s)

This system also provides us with derived units for various quantities, such as the poise for dynamic viscosity. Understanding and using the correct units consistently is essential for scientific accuracy and communication.

Poiseuille

Jean Léonard Marie Poiseuille was a French scientist known for his works in fluid dynamics. He notably studied the flow of blood through the veins, which led to the famous Hagen-Poiseuille equation for laminar flow. His work was foundational in understanding how fluids behave in both natural and engineered systems.
The unit named after him, the poise, reflects the significance of his contributions. It underscores how even complex properties like viscosity can be systematically measured and understood through established scientific principles. The poise measures the internal friction in a fluid, giving a sense of how easily a fluid can flow.

Dynamic Viscosity

In everyday terms, dynamic viscosity is how sticky or thick a fluid is. Scientifically, it's a measure of a fluid's resistance to flow, especially when it's subjected to external forces like a stirring rod or pumping.

• High viscosity means a fluid is thick, like honey or molasses.
• Low viscosity means a fluid is thin, like water or alcohol.

Dynamic viscosity is particularly important in engineering and various scientific fields, where understanding a fluid's behavior under different conditions is necessary. The standard unit for dynamic viscosity in the CGS system is the poise, where 1 poise equals 1 dyne-second per square centimeter.
For simpler calculations or international applications, the SI unit for dynamic viscosity is the pascal-second (Pa·s), where 1 Pa·s equals 10 poise. This conversion is crucial for fluid dynamics applications across global contexts.