Capillary rise

Capillary Rise Experiment – For Schools, Teachers, and Students

Definition

Capillary rise is the phenomenon where a liquid rises or falls in a narrow tube (capillary) due to the interplay between adhesive and cohesive forces. It occurs when the adhesive forces between the liquid and the tube wall are stronger than the cohesive forces within the liquid.

This concept is demonstrated in Dencity – Online Science Lab and Simulations to enhance interactive learning.

Theory

1. Capillary Action in Tubes

When a capillary tube is placed vertically in a liquid, the liquid rises or falls depending on the adhesive and cohesive forces.

• If adhesive forces between the liquid and the tube are stronger than cohesive forces, the liquid rises in the tube (e.g., water in glass).
• If cohesive forces within the liquid are stronger, the liquid depresses (e.g., mercury in glass).

The height to which the liquid rises or falls is given by:

$$Height=(2\times SurfaceTension\times cos(ContactAngle))/(Density\times Gravity\times RadiusofTube)$$

Key Factors Influencing Capillary Action:

• Capillary Rise: Occurs when the contact angle is less than 90 degrees (e.g., water in glass).
• Capillary Depression: Occurs when the contact angle is greater than 90 degrees (e.g., mercury in glass).
• Narrower tubes cause higher liquid rise due to increased adhesive force.
• Higher surface tension increases capillary action.

Examples of Capillary Action

1. Water in a Glass Capillary

• When a narrow glass tube is dipped in water, water rises due to strong adhesive forces between water and glass.

2. Mercury in a Glass Capillary

• When a glass capillary is dipped in mercury, the liquid depresses because cohesive forces within mercury are stronger than the adhesive forces with glass.

3. Water Movement in Soil

• Capillary action helps water move upward through soil pores, allowing plants to absorb moisture even in dry conditions.

4. Ink Movement in Pens

• Fountain pens and marker pens use capillary action to transfer ink to the paper without the need for external force.

Real-Life Uses of Capillary Action

• Transport of water in plants through xylem vessels.
• Wicking materials in fabrics, medical bandages, and face masks.
• Ink flow in pens, markers, and printers.
• Fluid movement in porous materials like bricks, sponges, and soil.

Observations

• Smaller capillary tubes result in a higher rise or depression of the liquid.
• Liquids with higher surface tension show greater capillary action.
• Contact angle determines whether the liquid rises or falls.
• Denser liquids experience less capillary rise due to increased weight.

This experiment helps students understand fluid mechanics and its applications in daily life, engineering, and nature.