00:02
So this problem wants us to determine how much heat passes through the window per second.
00:07
So what the problem is asking is the heat current through heat transfer by conduction.
00:14
So let's denote this as h.
00:21
And our interface here is window air window.
00:26
For heat transfer by conduction, this is the formula for heat current.
00:30
Thermal conductivity multiplied by the area over the thickness.
00:35
And this quantity multiplied by the temperature difference.
00:42
So from hot minus hot, hot temperature minus the cold temperature.
00:51
And note that this quantity is the reciprocal of thermal resistance, which we denote as r.
01:01
Then the formula for heat current will become like this.
01:10
And for this case, the heat current is equals to this.
01:26
Temperature difference over the total resistance.
01:31
And the total resistance here are the sum of each resistance of the material.
01:41
So we have two, since we have two windows of the same material, so two r window plus r of the air.
01:54
And from here we can derive an expression for the thermal resistance, and we can find that thermal resistance is equals to l over kt8.
02:09
For the window, it was stated that the length or the thickness, i mean, so l is thickness over product of thermal conductivity area.
02:30
It is not that it is equals to 0 .3 centimeters...