If we are wearing spectacles/sunglasses and step out of an AC car, why does vapour form on the glasses?

Question

Technical answers only please.

Answer 1

When your glasses are sufficiently cold, and you step into a hot environment, the water in the atmospheres condenses on the glasses. After a while, your glasses will absorb heat and the moisture on your lenses will once again turn into a gas. The condensation will be released back into the environment. That's also why a cold glass of water gets moisture on the outside. Atmospheric moisture condenses on the outside.

Answer 2

Good answers. Just to give a little more background info, the amount of water vapor that air can hold is a function of temperature. Hot air can hold more water vapor than cold air. Relative humidity is therefore a function of both the amount of water vapor in the air and the temperature of the air.

If you take air with a fixed amount of water vapor and cool it down, the relative humidity gradually increases until it reaches 100%. At that point (the dewpoint), further cooling will reduce the amount of water vapor which the air can hold below the actual amount, meaning some water vapor must condense out as liquid.

When you step out of the car AC on a humid day, a thin (laminar) layer of air right next to the glass lens gets cooled down below the dewpoint, and some water will therefore condense out on the cold lens. Just shake 'em like a polaroid picture, and they'll heat back up above the dp.

Answer 3

Air conditioning removes moisture from the air, rendering it very dry. The moisture condenses inside the AC unit, and, in home models, runs out a channel on the back. The AC unit of course cools the air as well.

So, after a long while in a cold car, your glasses are cold. When you step out into warm air that is also much closer to being saturated (maximum humidity), the cold glasses cause moisture to condense out of the air, forming droplets on your glasses.

You can observe a similar phenomenon if you take a bottle of cold water outside on a warm day. The moisture that forms on the outside has condensed out of the air.

Answer 4

I actual have worn glasses simply by fact that i became 11 and at the instant own 3 pairs. One pair I placed on distinctive the time, they have an anti mirrored image coating, I actual have a spare pair only in case and 2 prescription solar glasses - not often ever worn :-) As my lenses are small i don't hassle with bi or varifocals, I peer over the perfect while i could desire to study labels. Laser surgical operation isn't on the perfect of my want record, to boot my glasses are gentle-weight and that i not often be conscious them, basically while it rains or they get steamed up.

Answer 5

The temperature of the lenses is lower than the dew point of the air. This causes moisture to condense on the lenses