A wall has two layers A and B of equal areas.
Their thicknesses are 10 cm and 20cm.
Conductivity of A is twice that of B. Under
thermal equilibrium, if the temperature
difference across the wall is 45°C, then
temperature difference across the layer A is
1) 36°C 2) 27°C 3) 18°C4) 9°C
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Answer:
For thermal equilibrium,
Energy received by earth = Energy emitted by earth
4πd
2
T
s
4
⋅4πR
s
2
×πR
e
2
=σ⋅ρ⋅T
e
4
⋅4πR
e
2
4×d
2
×e
T
s
4
×R
s
2
=T
e
4
(Here, Emissivity of earth e=α×ρ)
⇒
4×(2×10
11
)
2
×0.6
(6000)
4
×(7×10
8
)
2
=T
e
4
⇒
4×4×0.6
36×36×7×7
×10
6
=T
e
4
⇒66.15×108=T
e
4
T
e
=300K.
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