What must be the lengths of steel and copper rods at $0^o C$ for the difference in their lengths to be $10\,cm$ at any common temperature? $(\alpha_{steel}=1.2 \times {10^{-5}} \;^o C^{-1})$ and $(\alpha_{copper} = 1.8 \times 10^{-5} \;^o C^{-1})$

  • A

    $30\, cm$ for steel and $20\,cm$ for copper

  • B

    $20\,cm$ for steel and $30\,cm$ for copper

  • C

    $40\,cm$ for steel and $30\,cm$ for copper

  • D

    $30\,cm$ for steel and $40\,cm$ for copper

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