Physics 2003 JAMB Past Questions - Question 8: Water does not drop through an open umbrella of silk material unless the inside of the umbrella is touched. This is due to

Correct Answer

D

Explanation

Water does not drop through an open umbrella made of silk material unless the inside of the umbrella is touched because of the surface tension of water and the hydrophobic properties of silk.

1. **Surface Tension:** Water has a property called surface tension, which causes water molecules to be attracted to each other and form a sort of "skin" on the surface of the liquid. When water comes into contact with a hydrophobic (water-repelling) surface like silk, it tends to bead up and not readily penetrate the material. This is because the cohesive forces between water molecules are stronger than the adhesive forces between water and the silk fabric.

2. **Hydrophobic Nature of Silk:** Silk is a natural protein fiber and has hydrophobic characteristics. The surface of silk is not naturally inclined to allow water to pass through it. The water droplets tend to bead up and sit on the surface of the silk fabric.

When you touch the inside of the silk umbrella, you disrupt the surface tension and allow water to flow through. The water then wets the silk fabric on the inside, and it may start to drip through the umbrella. This effect is a demonstration of the hydrophobic properties of silk and the surface tension of water.