Help me to find it out

[JamSmith]

Hi everyone,

 

I was solving some real time physics question and come across this question.

I have tried to find out the perfect answer but couldn't satisfied with my analysis. Can anyone guide me?

 

On a cold, dry winter day your glasses fog up when you go indoors after being outside for a while. Why is that?

And if you go back outside with your glasses still fogged up, they quickly clear up. Why is that?

Edited March 2, 2017 by JamSmith

[studiot]

Hi everyone,

 

I was solving some real time physics question and come across this question.

I have tried to find out the perfect answer but couldn't satisfied with my analysis. Can anyone guide me?

 

On a cold, dry winter day your glasses fog up when you go indoors after being outside for a while. Why is that?

 

And if you go back outside with your glasses still fogged up, they quickly clear up. Why is that?

 

This is a really good way to go about discussing a subject. +1

 

You have presented some basic observations, are they complete?

 

That is

 

Have you considered both plastic and glass lenses?

 

Which side of the lens fogs up, or is it both?

This is an important question that provides a clue to the answer.

 

Have you looked at other glass/plastic objects, for instance window panes?

 

Which side of a window pane fogs up?

[J.C.MacSwell]

What is the dew point of the air in the house vs the air outside?

[JamSmith]

What is the dew point of the air in the house vs the air outside?

I am not sure about it, may be 20° C or below

 

This is a really good way to go about discussing a subject. +1

 

You have presented some basic observations, are they complete?

 

That is

 

Have you considered both plastic and glass lenses?

 

Which side of the lens fogs up, or is it both?

This is an important question that provides a clue to the answer.

 

Have you looked at other glass/plastic objects, for instance window panes?

 

Which side of a window pane fogs up?

I have only tried it on glass.

 

If Discussiong about Window panes then I observed that when Cooling outside the window fog up inside.

 

The higher the dew point, the longer it will take for the glasses to clear.

[Klaynos]

And what is the dew point in terms of what it means?

[swansont]

Also think about what is happening when something "fogs up"

 

Have you ever noticed anything fogging up in, say, the bathroom, after taking a shower?

[JamSmith]

And what is the dew point in terms of what it means?

The dew point is the temperature at which air is saturated with water vapor, which is the gaseous state of water.

I have also read that Dew point is closely linked to relative humidity, which is the ratio of the pressure of water vapor in a parcel of air relative to the saturation pressure of water vapor in that same parcel of air at a specific temperature.

 

Is this satisfying description?

Also think about what is happening when something "fogs up"

 

Have you ever noticed anything fogging up in, say, the bathroom, after taking a shower?

Yes, I have noticed that, and also research on it last night.

 

I sum up with this:

 

The fog in the mirror is the moisture of water vapor as it abuts a colder surface. With the cold water, we just cool down the bathroom. So the vapor came from the hot shower, mostly condense and will not reach the mirror.

 

At the same time, if we do something opposite like vapor comes from heat or hot air will become less likely on the warmer surface.

 

For air containing a certain amount of moisture, there is a maximum temperature at which the water will Epitomize. This is called the dew point.

 

Right?

[swansont]

The fog in the mirror is the moisture of water vapor as it abuts a colder surface. With the cold water, we just cool down the bathroom. So the vapor came from the hot shower, mostly condense and will not reach the mirror.

 

At the same time, if we do something opposite like vapor comes from heat or hot air will become less likely on the warmer surface.

 

For air containing a certain amount of moisture, there is a maximum temperature at which the water will Epitomize. This is called the dew point.

 

Right?

What cold water? You have moisture in the air, and it condenses on the mirror. The water vapor loses energy when it contacts the surface, and forms small droplets.