Problem 55 - A Complete Resource Book in Chemistry for JEE Main

Question

The unit of surface tension is (a) Joule \(\mathrm{m}^{-1}\) (b) \(\mathrm{N} \mathrm{m}^{-1}\) (c) \(\operatorname{erg} \mathrm{cm}^{-1}\) (d) none of these

Step-by-Step Solution

Answer

The unit of surface tension is (b) N m^{-1).

Step 1: Understanding Surface Tension

Surface tension is a force that acts on the surface of a liquid. It acts along the surface and is typically measured in force per unit length.

Step 2: Si Unit of Surface Tension

The standard unit of force is the Newton (N) and the standard unit of length is the meter (m), therefore, the SI unit for surface tension is Newton per meter (N m^{-1}).

Step 3: Analyzing Provided Options

Let's examine the given options to find which matches the derived SI unit. Option (b) is N m^{-1}, which is the correct SI unit for surface tension.

Step 4: Final Decision

After our analysis, the SI unit of surface tension, N m^{-1}, corresponds to option (b) among the given options.

Key Concepts

SI Units

In physics, standardizing units across measurements is vital to ensure consistency and accuracy. These standardized measurements are referred to as SI Units, or the International System of Units.
Standardization helps scientists around the world to understand and share data without confusion. The SI system is based on seven base units such as meter for length, kilogram for mass, and second for time.
The SI unit of force is the Newton (N), and it plays a crucial role in various physical calculations, including surface tension. In the case of surface tension, which is a measure of the force along the surface of a liquid, it is expressed as force per unit length. This means that the SI unit for surface tension would be Newton per meter (N/m).
Standardizing these units allows individuals to exchange complex data easily and ensure everyone is on the same terms with physical quantities.

Force per Unit Length

Surface tension can be understood as a special type of force acting along a liquid's surface. This force arises due to the cohesive forces between liquid molecules.
Imagine a thin line placed on a liquid surface. Surface tension acts along this line, pulling the molecules inward towards the liquid body.
Thus, we measure surface tension in terms of force per unit length. The force exerted is measured in Newtons, while the length is measured in meters. The resulting unit is Newton per meter (N/m).

• This unit signifies the amount of force in Newtons that acts along each meter of a surface line.
• It provides an understanding of the intensity of molecular forces per unit length of the liquid surface.

Understanding the concept of force per unit length helps to analyze phenomena like the formation of droplets and the wetting properties of liquids.

Physics Concepts

Physics is filled with intriguing concepts that explain the natural world, among which surface tension is quite compelling. It involves understanding how molecules at the surface of a liquid interact with each other and the environment.
The idea behind surface tension is based on molecular attraction. Molecules within the liquid are surrounded by other molecules from all sides, creating an even balance of forces. However, molecules at the surface experience a net inward pull, as they are not surrounded above by liquid molecules.
This net force causes the surface to behave like an elastic film, minimizing its area. Real-life manifestations of surface tension include insects walking on water and soap bubbles forming perfect spheres.

• These occurrences rely on the forces acting parallel to the liquid surface and the cohesive forces between molecules.
• Examining surface tension as a physics concept aids in understanding diverse natural phenomena and technological applications.

Physics concepts like these demonstrate the complexity and richness of the natural world, offering a deeper insight into how and why things happen as they do.