There is formation of layer of snow $x\,cm$ thick on water, when the temperature of air is $ - {\theta ^o}C$ (less than freezing point). The thickness of layer increases from $x$ to $y$ in the time $t$, then the value of $t$is given by
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(a) Since $t = \frac{{\rho L}}{{2k\theta }}(x_2^2 - x_1^2)$
$\therefore $$t = \frac{{\rho L}}{{2k\theta }}({x^2} - {y^2}) = \frac{{\rho L(x + y)(x - y)}}{{2K\theta }}$
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