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If \mathrm{K_{1}} and \mathrm{K_{2}} are the thermal conductivities, \mathrm{L_{1}} and \mathrm{L_{2}} are the lengths and \mathrm{A_{1}} and \mathrm{A_{2}}  are the cross sectional areas of steel and copper rods respectively such that \mathrm{\frac{K_{2}}{K_{1}}=9, \frac{A_{1}}{A_{2}}=2, \frac{L_{1}}{L_{2}}=2}.  Then, for the arrangement as shown in the figure, the value of temperature  \mathrm{T}  of the steel - copper junction in the steady state will be : 

Option: 1

\mathrm{18^{\circ} \mathrm{C}}


Option: 2

\mathrm{14^{\circ} \mathrm{C}}


Option: 3

\mathrm{45^{\circ} \mathrm{C}}


Option: 4

\mathrm{150^{\circ} \mathrm{C}}


Answers (1)

best_answer

Let the heat current flowing through steel and Copper 

\mathrm{ H_1 =H_2 }

\mathrm{\frac{K_1 A_1(450-T)}{\ell_1} =\frac{K_2 A_2(T-0)}{\ell_2} }

\mathrm{2(450-T) =9 \times 2(T) }

\mathrm{\\ 450-T =9 T}

\mathrm{10 T =450 }

\mathrm{T =45^{\circ}}

Hence 3 is correct option.

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Gunjita

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