A double-paned window has two glass panes separated by a layer of air. Why is air, rather than glass, used to fill this space? HELP PLEASE!!!!!!!!!

Question

 

A. The conduction of heat is slowed by the air.

B. The convection of heat is increased by the air.

 

C. The radiation of heat is increased by the air.

D. The convection of heat is slowed by the air.

Answer 1

I know I am very late to the party, and no one probably cares anymore, but I think the previous answer is mistaken.

 

The main error, I think, is in the imprecise definitions of the various kinds of heat transfer.  I think a more accurate description is:

 

conduction:  the transfer of hear without the bulk motion of material.  This means that heat is transferred without any part of the material moving to a different location.  This is common in solids, because the material is often not free to move very much.  Heat is transferred principally by the jiggling of one atom pulling on the atom next to it, which pulls on the atom next to it, and so on.  But no part of the material breaks off and moves to another location (because it can't).

 

convection:  the transfer of heat BY the bulk motion of material.  This is more common in liquids and gases, where whole sections of the material can move together to another part of the medium.  An example of this is a "rolling boil" of water in a heated pot.  The water is rolling because whole sections of it are moving from the bottom (where they absorb heat from the solid pan by conduction) to the top (where heat is released to the surroundings).  The heat is being conveyed by the material; hence, convection.

 

radiation:  the transfer of thermal energy by electromagnetic radiation (no medium required).  This is not limited to infrared radiation.  In fact, in the glowing spoon example from the previous answer, the glowing must actually be visible radiation.  Any wavelength of light can transfer thermal energy by radiation.  The main attribute is that it does not require a medium.

 

I often illustrate this in class by taking an eraser to the back of the class (representing a quantity of heat), and having it sent back to me in various ways.  First, the students (the medium) pass it from one to another until it gets back to me.  The heat moved to me, even though no student had to leave their seat.  That is conduction.  Then, I have a student in the back carry the eraser up to me.  The student changed position to carry the heat to me.  That is convection.  Finally, I have a student pass me the eraser like a football from the back of class.  Disregarding the launch, this transfer required no medium involvement at all to get the eraser back to me.  That's radiation.

 

In the case of the window, the main heat transfer method from inside to outside is conduction.  If there were only one solid pane of glass, conduction would be fairly strong.  However, because air is not as dense as glass, it conducts heat much less well.  So having an air gap very much slows the conduction of heat outside (when it is cooler outside) or inside (when it is cooler inside).  

 

On this basis, I think the answer should be A.

 

Now, if the gap were wide enough that a reasonable amount of air flow could start, the air could conduct heat by convection, which is a much more efficient way for air to conduct heat.  So the gap needs to be narrow enough so this does not happen.  But since it is the size of the gap, and not the air itself, that slows convection, I do not think this fits with answer D.

 

Answer 2

To help, you need to know about the transfer of heat.  

 

 

Conduction of heat is created when two objects are in contact with one another and the heat is transferred between them.  In this case, it would be like touching a hot spoon onto ice cream.  The ice cream would melt pretty fast due to the the conductive transfer of heat.

 

Convection is the transfer of heat from the area and its environment.  This would be like putting a hot metal spoon NEAR the ice cream but not directly on it.  The ice cream would melt but not as quickly since there is no direct contact.

 

Radiation of heat is the transfer of heat in the way of infrared light.  In this case, if you heated up the spoon until it was glowing, that would be radiation.

 

 

Now then, a double-paned window is used to trap heat inside and keep excess heat outside.  When it comes to the nature of any kind of energy it slows down when it goes through a different medium.  Since you're trying to alter the transfer of heat from its environment, the answer should now become obvious.