Why do glasses fog up?
Show answer & explanation
Answer: Water vapor condenses on cool lens
Breath contains particles — Wrong. Breath has moisture (water vapor), but fogging occurs when vapor condenses to liquid on cool surface, not particle deposition.
Water vapor condenses on cool lens ✓ — Correct! Warm air holds more moisture (water vapor) than cool air. Warm breath meets cold glasses—air cools rapidly, can't hold as much moisture. Water vapor condenses into tiny liquid droplets on lens—fog! Dewpoint: temperature where air becomes saturated. Same principle: bathroom mirrors after shower, car windows in winter. Anti-fog coatings reduce surface tension, preventing droplet formation!
Temperature creates tiny clouds — Wrong. Temperature difference drives process, but specific mechanism is condensation—water vapor becoming liquid droplets on cool surface.