Question

The spherical shape of liquid drops is due to (1) viscosity (2) vapour pressure (3) surface tension (4) molecular size

Short answer

Surface tension

Step-by-step solution

Define the spherical shape formation

The spherical shape of liquid drops is formed to minimize the surface area for a given volume.

Analyze the options

Consider the effects of viscosity, vapour pressure, surface tension, and molecular size on the shape of liquid drops.

Focus on surface tension

Surface tension acts to pull the liquid molecules towards each other, minimizing the surface area and resulting in a spherical shape.

Conclusion

Understand that none of the other factors (viscosity, vapour pressure, molecular size) contribute as directly as surface tension to the spherical shape of liquid drops.

Key concepts

Spherical Shape of Droplets

When you observe droplets of liquid, particularly small ones like dew on a leaf, you will notice they are often nearly perfect spheres. This spherical shape is not random but occurs because it allows the droplet to minimize its surface area for its volume. This phenomenon is primarily due to surface tension.

Surface tension is the cohesive force between liquid molecules at the surface. It acts to pull the molecules closer together, minimizing the surface area. Since the sphere has the smallest surface area for a given volume, liquid droplets naturally adopt this shape to reduce the energy associated with the surface. This is why you will often find small liquid droplets in a spherical form in nature.

To summarize, the spherical shape helps to minimize the liquid's surface area, which reduces the energy associated with the formation of the surface.

Minimizing Surface Area

In physics, minimizing energy is a key principle, and surface tension is a force that drives this when it comes to liquids. By forming a sphere, a droplet of liquid can achieve the smallest possible surface area for the amount of volume it contains. This is important because more surface area means more surface molecules are exposed, which increases the potential energy.

Here are a few points to understand how surface tension minimizes surface area:

• Surface molecules are attracted inward, creating a tightening effect.
• This inward pull reduces the overall surface area of the liquid.
• Because a sphere has the least surface area for a given volume, droplets naturally adopt this shape to go against the surface tension.

In conclusion, minimizing surface area is a way for liquid droplets to achieve a state of lower energy, leading to the formation of spherical shapes.

Factors Affecting Liquid Droplets

While surface tension is the primary force shaping liquid droplets into spheres, several other factors also play a role in the behavior of liquid droplets. Here are the key factors:

• Viscosity: This is the measure of a liquid's resistance to deformation. For droplets, higher viscosity means they are slower to change shape and can resist external forces better, but it does not primarily determine the spherical shape.
• Vapour Pressure: This influences how quickly a liquid evaporates. While it plays a role in the behavior and stability of droplets, it does not directly affect their shape.
• Molecular Size: The size of molecules affects the overall properties of the liquid, like density and viscosity. However, alone, it does not decide the droplet's shape.

Thus, while viscosity, vapour pressure, and molecular size influence the behavior and properties of liquids, surface tension is the main factor that dictates the spherical shape of droplets.