Question

To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.

Answer 1

Wetting of spectacles :

• Humans inhale oxygen $\left({\mathrm{O}}_2\right)$ from the atmosphere and exhale Carbon Dioxide $\left({\mathrm{CO}}_2\right)$.
• We exhale water vapor $\left({\mathrm{H}}_2\mathrm{O}\right)$ along with carbon dioxide $\left({\mathrm{CO}}_2\right)$ gas when we breathe out.
• When water vapor strikes a glass surface, it condenses and causes the glass to become wet.
• Condensation is the process of conversion of gaseous vapors into the liquid phase at atmospheric temperature.
• The same phenomenon is responsible for the wetting of glasses when we breathe out.
• A soft towel can be used to quickly clean this somewhat damp glass.