Find effective thermal resistance between $A$ & $B$ of cube made up of $12$ rods of same dimensions and shown given thermal conductivity. [ $l =$ length of rod, $a =$ cross section area of rod]
  • A$\frac{l}{{ka}}$
  • B$\frac{2l}{{ka}}$
  • C$\frac{4l}{{7ka}}$
  • D$\frac{l}{{2ka}}$
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