==> % increase in energy $ = \frac{{{Q_2} - {Q_1}}}{{{Q_1}}} \times 100 = 46\% $
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A slab consists of two parallel layers of copper and brass of the same thickness and having thermal conductivities in the ratio $1 : 4$ . If the free face of brass is at ${100^o}C$ and that of copper at $0^\circ C $, the temperature of interface is ........ $^oC$
Suppose the sun expands so that its radius becomes $100$ times its present radius and its surface temperature becomes half of its present value. The total energy emitted by it then will increase by a factor of
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