Two parallel plates in vacuum, separated by a distance which is small compared with their linear dimensions, are at temperatures 
and 
respectively ( 
).
A
If the plates are non-transparent to radiation and have emission powers 
and 
respectively, show that the net energy W transferred per unit area per second is 
where 
and 
are the emission powers of black bodies at temperatures 
and 
respectively.
and respectively, show that the net energy W transferred per unit area per second is where and are the emission powers of black bodies at temperatures and respectively. B
Hence, what is W if 
is 300 K and 
is 4.2 K , and the plates are black bodies?
?
is 300 K and is 4.2 K , and the plates are black bodies? ?
C
What will W be if n identical black body plates are interspersed between the two plates in
Text Solution
Verified by ExpertsThe correct answer is:
CHECK THE SOLUTION.
Let 
and 
be the total emission powers (thermal radiation plus reflection) of the two plates respectively. We have
The solution is
Hence
For black bodies, 
.
Assume that the n interspersed plates are black bodies at temperatures 
. When equilibrium is reached, we have
with solution
with solution
Then in the general we have
with solution
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