Test: Surface Tension - UPSC MCQ

Surface tension is the force that acts perpendicular to the surface of a liquid, creating a "skin-like" effect.

Surface tension is caused by cohesive forces between the molecules of a liquid, which attract each other and create a tension at the surface.

Surface tension is affected by temperature, pressure, and impurities in the liquid. These factors can alter the strength of the cohesive forces between liquid molecules.

Due to surface tension, surface tries to minimize its area. As sphere has the minimum surface area among all geometrical shapes thus, liquid drop becomes spherical.

Surface tension generally decreases with an increase in temperature. The increased kinetic energy of the molecules weakens the cohesive forces, reducing surface tension.

Capillary rise in a narrow tube is due to surface tension. The adhesive forces between the liquid and the tube's walls pull the liquid upward.

Mercury has the highest surface tension among the given options. Its cohesive forces are strong, resulting in a high resistance to deformation.

Surface tension explains the formation of raindrops (coalescence of water droplets), floating of a needle on water (surface tension supports the needle), and the rise of oil in a lamp wick (capillary action).

The contact angle between a liquid and a solid surface is minimum when there is complete wetting of the solid by the liquid. Adhesion dominates over cohesion.

Surfactants are substances that lower the surface tension of a liquid. They disrupt the cohesive forces between liquid molecules, reducing surface tension.

The formation of soap bubbles is due to surface tension. The soap solution lowers the surface tension, allowing the thin films of liquid to form bubbles.

An angle of contact of 180° indicates no wetting of the solid by the liquid. The liquid does not spread on the solid surface.

The rise or fall of liquid in a capillary tube is inversely proportional to the radius of the tube.A smaller radius results in a higher capillary rise, as the surface tension dominates over gravity.

Capillary action is a phenomenon due to surface tension. The adhesive forces between the liquid and the capillary walls, along with cohesive forces within the liquid, cause it to rise or fall in the tube.

Honey has a higher viscosity compared to water, alcohol, and gasoline. It flows more slowly due to the stronger cohesive forces between its molecules.

The viscosity of a liquid can be affected by temperature, pressure, and molecular size, but color of the liquid has no impact on the viscosity of a liquid

Stronger intermolecular forces, such as hydrogen bonding, result in higher surface tension because the cohesive forces between molecules are stronger.

Viscosity is the property of a liquid that resists its flow. It is related to the internal friction between molecules within the liquid.

Since surface tension is force per unit length, its unit will be unit of force / unit of length = Newton / meter
Unit of force is newton and the unit of length is meter. So,  unit of surface tension is Newton/meter

Capillarity is used in various natural and mechanical systems. In plants, it helps in the movement of water through capillary tubes. In animals, it aids in the functioning of capillary networks. Machines can utilize capillary action for liquid transfer and other applications.