Two rods are joined between fixed supports as shown in the figure. Condition for no change in the lengths of individual rods with the increase of temperature will be
( ${\alpha _1},\,{\alpha _2},$ = linear expansion coefficient
$A_1, A_2$ = Area of rods
$Y_1, Y_2$ = Young modulus)
$\frac{{{A_1}}}{{{A_2}}}\, = \,\frac{{{\alpha _1}{Y_1}}}{{{\alpha _2}{Y_2}}}$
$\frac{{{A_1}}}{{{A_2}}}\, = \,\frac{{{L_1}{\alpha _1}{Y_1}}}{{{L_2}{\alpha _2}{Y_2}}}$
$\frac{{{A_1}}}{{{A_2}}}\, = \,\frac{{{L_2}{\alpha _2}{Y_2}}}{{{L_1}{\alpha _1}{Y_1}}}$
$\frac{{{A_1}}}{{{A_2}}}\, = \,\frac{{{\alpha _2}{Y_2}}}{{{\alpha _1}{Y_1}}}$
A unit scale is to be prepared whose length does not change with temperature and remains $20\,cm$, using a bimetallic strip made of brass and iron each of different length. The length of both components would change in such a way that difference between their lengths remains constant. If length of brass is $40\,cm$ and length of iron will be$...cm$
$\left(\alpha_{\text {iron }}=1.2 \times 10^{-5} K ^{-1}\right.$ and $\left.\alpha_{\text {brass }}=1.8 \times 10^{-5} K ^{-1}\right)$.
A steel meter scale is to be ruled so that millimeter intervals are accurate within about $5 \times 10^{-5}$ $mm$ at a certain temperature. The maximum temperature variation allowable during the ruling is .......... $^oC$ (Coefficient of linear expansion of steel $ = 10 \times {10^{ - 6}}{K^{ - 1}})$
$Assertion :$ In pressure-temperature $(P-T)$ phase diagram of water, the slope of the melting curve is found to be negative.
$Reason :$ Ice contracts on melting to water.
On what value of $\alpha _l$ depends ? Write its unit.
A cuboid $ABCDEFGH$ is anisotropic with $\alpha_x = 1 × 10^{-5} /^o C$, $\alpha_y = 2 × 10^{-5} /^o C$, $\alpha_z = 3 × 10^{-5} /^o C$. Coefficient of superficial expansion of faces can be