A room has s window fitted with a single `1.0mxx2.0m` glass of thickness 2mm. (a) Calculate the rate of heat flow through the closed window when the temperature inside the room is `32^(@)C` and that outside is `40^(@)C` . (b) The glass is now replaced by two glasspanes, each having a thickness of 1mm and separated by a distance of 1mm. Calculate the rate of heat flow under the same condition of temperature. Thermal conductivity of window glass `=1.0Js^(-1)m^(-1)C^(-1)` and that of air `=0.025Js^(-1)m^(-1)C^(-1)` .

Answer

A, B, C

Explanation

`(a) Q/t=(kA(theta_1-theta_2))/(1)`
`=(1xx2xx(40-32))/(2xx10^(-3))`
`=8000 J//sec.`
(b)resistance of glass =`1/(ak_g)+1/(ak_g)`
Resistance of air =`1/(ak_g)`
Net resistance =`1/(ak_g)+1/(ak_a)+1/(ak_g)`
`=1/(a)((2)/(k_g)+(1)/(k_a))`ltbr.`1/a((2k_g +kg)/(k_g k_a))`
`=(1xx10^(-3)xx1.05)/0.05`
`Q/t=(theta_1-theta_2)/R`
`=385.9=381 W.