rod of $40\, cm$ in length and temperature difference of ${80^o}C$ at its two ends. $A$ nother rod $B$ of length $60\, cm$ and of temperature difference ${90^o}C$, having the same area of cross-section. If the rate of flow of heat is the same, then the ratio of their thermal conductivities will be

  • A

    $3:4$

  • B

    $4:3$

  • C

    $1:2$

  • D

    $2:1$

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