Two bars of thermal conductivities $K$ and $3K$ and lengths $1\,\, cm$ and $2\,\, cm$ respectively have equal cross-sectional area, they are joined lengths wise as shown in the figure. If the temperature at the ends of this composite bar is $0\,^oC$ and $100\,^oC$ respectively (see figure), then the temperature $\varphi $ of the interface is......... $^oC$

818-871

  • A

    $50$

  • B

    $\frac{{100}}{3}$

  • C

    $60$

  • D

    $\frac{{200}}{3}$

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  • [AIIMS 1998]

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