A slender rod of length L, diameter d (L >> d) and thermal conductivity k1 is joined with another rod of identical dimensions, but of thermal conductivity k2, to form a composite cylindrical rod of length 2L. The heat transfer in radial direction and contact resistance are negligible. The effective thermal conductivity of the composite rod is

\(\frac{{{k_1}{k_2}}}{{{k_1} + {k_2}}}\)

\(\frac{{2{k_1}{k_2}}}{{{k_1} + {k_2}}}\)

A slender rod of length L, diameter d (L >> d) and thermal conductivit

1.	A slender rod of length L, diameter d (L >> d) and thermal conductivity k1 is joined with another rod of identical dimensions, but of thermal conductivity k2, to form a composite cylindrical rod of length 2L. The heat transfer in radial direction and contact resistance are negligible. The effective thermal conductivity of the composite rod is
A.	k1 + k2
B.	\(\sqrt {{k_1}{k_2}}\)
C.	\(\frac{{{k_1}{k_2}}}{{{k_1} + {k_2}}}\)
D.	\(\frac{{2{k_1}{k_2}}}{{{k_1} + {k_2}}}\)
Answer» E.

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