A) 3 : 5
B) 5 : 3
C) 3 : 4
D) 3 : 2
Correct Answer: B
Solution :
The thermal resistance of a rod of length\[l,\] area of cross-section A and thermal conductivity K, is \[R=\frac{l}{KA}\] Given, thermal resistance of rods is equal therefore, also\[{{A}_{1}}={{A}_{2}}\] \[\frac{{{l}_{1}}}{{{K}_{1}}{{A}_{1}}}=\frac{{{l}_{2}}}{{{K}_{2}}{{A}_{2}}}\] \[\Rightarrow \] \[\frac{{{l}_{1}}}{{{K}_{1}}}=\frac{{{l}_{1}}}{{{K}_{2}}}\] \[\Rightarrow \] \[\frac{{{l}_{1}}}{{{l}_{2}}}=\frac{{{K}_{1}}}{{{K}_{2}}}=\frac{5}{3}\]
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