Cotton is a good absorber of water and exposes sweat to the atmosphere for easy evaporation.
Explanation
The scientific basis for wearing cotton in summer lies in the physical phenomenon of evaporative cooling. Cotton, being a natural cellulosic fibre, possesses high hygroscopicity (water-absorbing capacity), which is essential for managing perspiration in hot conditions.
Detailed Analysis:
- Mechanism of Cooling: During summer, the human body perspires to regulate body temperature. Cotton fabric effectively absorbs this sweat and spreads it over a larger surface area. This exposes the moisture to the atmosphere, facilitating rapid evaporation.
- Latent Heat of Vaporization: As the sweat evaporates, it requires energy to change state from liquid to gas. This energy, known as the latent heat of vaporization, is absorbed from the body, thereby lowering the body temperature and providing a cooling sensation.
- Analysis of Incorrect Options:
- Cotton is a poor conductor of heat.: While cotton is a poor conductor of heat, this property is generally associated with insulation (trapping air) rather than the active cooling mechanism required in summer.
- Cotton has a light colour which reflects sunlight.: The reflection of sunlight depends on the colour of the fabric (white vs. black), not the material itself. Cotton can be dyed dark, which would absorb heat.
- Cotton fibres are loosely packed allowing air circulation.: While cotton is porous and allows air circulation, the primary cooling mechanism distinguishing it from synthetic fibres (which may also be woven loosely) is its ability to absorb moisture and facilitate evaporation. Synthetic fibres tend to trap sweat, causing discomfort.
Key Takeaway:
Cotton is recommended in summer because it absorbs sweat and facilitates evaporation, which extracts latent heat from the body, causing a cooling effect.