Two identical rectangular rods of metal are welded end to end in series between temperature \[0{}^\circ C\] and \[100{}^\circ C\] and 10 J of heat is conducted (in steady state process) through the rod in 2.00 min. If 5 such rods are taken and joined as shown in figure maintaining the same temperature difference between A and B, then the. time in which 20 J heat will flow through the rods is: |
A) 30 sec.
B) 2 min.
C) 1 min.
D) 20 sec.
Correct Answer: C
Solution :
\[\frac{dQ}{dt}=\frac{KA\,\Delta \,T}{2\ell }=\frac{\Delta \,T}{\frac{2\ell }{KA}}=\frac{10}{120}J/sec.\] |
New rate \[\frac{dQ}{dt}=\frac{\Delta \,T}{\frac{\ell }{2\,KA}}=\frac{40}{120}J/sec.\,\,;\] |
So time taken is \[t=\frac{20}{40}\times 120\,\sec .=60sec.\] |
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