| Five identical rods are connected between two large reservoirs of temperatures \[100{}^\circ C\] and \[0{}^\circ C\]. Each rod has thermal conductivity k, length l, and area A. |
| There is no heat transfer through sides of rods. |
 |
| Heat flow rate from reservoir A to B is |
A) \[\frac{100kA}{l}\]
B) \[\frac{100kA}{7l}\]
C) \[\frac{100kA}{3l}\]
D) \[\frac{100kA}{13l}\]
Correct Answer: A
Solution :
| Rods are connected as, |
 |
| Following electrical analogy no heat current flows through rod 2. |
| So, equivalent thermal resistance of network is |
 |
| \[{{\operatorname{R}}_{eq}}=\frac{2R\times 2R}{2R+2R}=R=\frac{l}{kA}\] |
| So, heat flow rate through network is |
| \[H=\frac{\Delta T}{{{\operatorname{R}}_{eq}}}=\frac{100kA}{l}\] |
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