Three identical rods A.B and C of equal lengths and equal diameters are joined in series as shown in figure. Their thermal conductivities are 2k,k and k/2 respectively. The temperatures at two junction points are
A
85.7, 57.1∘C
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B
80.85, 50.3∘C
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C
77.3, 48.3∘C
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D
75.8, 49.3∘C
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Solution
The correct option is C 85.7, 57.1∘C Governing equation: ˙Q=KAΔTl Heat flowing through all the rods is the same, and all rods have same lengths and cross sectional areas. I.e. ˙QlA=KΔT=constant; I.e. 0.5K(T2−0)=K(T1−T2)=2K(100−T1) Combining any two of those equations and solving we get T1=85.7 and T2=57.1