Question

Why is the glass covered with a thin layer of moisture when breathing?

Answer 1

in colder days when we exhale moist air, moist air is at higher temperature ( generally at body temperature) as compare to the surrounding.

when moist air comes in contact with glass (which is at lower temperature), moisture in air looses its latent heat & condenses on glass surface.

this happens only when glass temperature lower than dew point temperature of moist air.

{generally in colder days}

*dew point temperature of air : temperature at which water vapour in air condenses into liquid water.