A steel rod is $4.000 \mathrm{cm}$ in diameter at $30 °\mathrm{C}$ . A brass ring has an interior diameter of $3.992 \mathrm{cm}$ at $30 °\mathrm{C}$ . In order that the ring just slides onto the steel rod, the common temperature of the two should be

$\left({\mathrm{\alpha }}_{\mathrm{steel}}=11\times {10}^{-6}/ °\mathrm{C}\mathrm{ }\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{ }{\mathrm{\alpha }}_{\mathrm{brass}}=19\times {10}^{-6}/ °\mathrm{C}\right)$