A) 30 sec.
B) 2 min.
C) 1 min.
D) 20 sec.
Correct Answer: C
Solution :
[C]\[\frac{dQ}{dt}=\frac{KA\Delta T}{2\ell }=\frac{\Delta T}{2\ell }=\frac{10}{120}J/sec.\] |
New rate \[\frac{dQ}{dt}=\frac{\Delta T}{\frac{\ell }{2KA}}=\frac{40}{120}J/sec.\,\,;\] |
So time taken is \[t=\frac{20}{40}\times 120\sec ,=60\,\sec .\] |
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