Two rods $A$ and $B$ of different materials are welded together as shown in  figure.Their thermal conductivities are $K_1$ and $K_2$  The thermal conductivity of the composite rod will be
  • A$\frac{{3{K_1}{K_2}}}{2}$
  • B$\frac{{{K_1} + {K_2}}}{3}$
  • C$\;\frac{{{K_1}{K_2}}}{{3({K_1} + {K_2})}}$
  • D$\;\frac{{{K_1} + {K_2}}}{2}$
NEET 2017, Medium
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