Surface Tension Concept Explanation

Surface tension is the property of a liquid that allows it to resist external forces due to the cohesive nature of its molecules. In this problem, a liquid film supports a weight through surface tension forces.

Step 1: Understand the Setup

A U-shaped wire holds a liquid film with a light slider of length 30 cm. The weight supported is $W=1.5\times {10}^{–2}\text{N}$. The slider has negligible weight.

Step 2: Identify Forces

The liquid film has two surfaces (front and back), each exerting surface tension force. The total upward force due to surface tension balances the weight.

Surface tension force from one surface: $F=T\times L$, where $T$ is surface tension and $L$ is length.

Total upward force = $2TL$ (since two surfaces)

Step 3: Apply Equilibrium Condition

At equilibrium: Total upward force = Weight supported

Step 4: Substitute Values

Length $L=30\text{cm}=0.3\text{m}$

Weight $W=1.5\times {10}^{–2}\text{N}$

Equation becomes: $2T\times 0.3=1.5\times {10}^{–2}$

Step 5: Solve for Surface Tension T

Final Answer

The surface tension of the liquid film is $0.025\text{Nm}–1$

Related Topics

• Capillary Action
• Cohesive and Adhesive Forces
• Meniscus Formation
• Surface Energy

Important Formulae

Surface Tension: $T=\frac{F}{L}$

Excess Pressure in Soap Bubble: $P=\frac{4T}{R}$

Capillary Rise: $h=\frac{2T\cos \theta }{\rho gr}$