A sphere and a cube of same material and same volume are heated upto same temperature and allowed to cool in the same surroundings. The ratio of the amounts of radiations emitted will be

- A
$1 :1$

- B
$\frac{{4\pi }}{3}:1$

- C
${\left( {\frac{\pi }{6}} \right)^{\frac{1}{3}}}:1$

- D
$\frac{1}{2}{\left( {\frac{{4\pi }}{3}} \right)^{\frac{2}{3}}}:1$

Two sheets of thickness $d$ and $2 d$ and same area are touching each other on their face. Temperature $T_A$, $T_B$, $T_C$ shown are in geometric progression with common ratio $r = 2$. Then ratio of thermal conductivity of thinner and thicker sheet are

A body cools from $62\,^oC$ to $50\,^oC$ in $10\, minutes$ and to $42\,^oC$ is next $10\, minutes$. The temp. of surrounding is ........ $^oC$

The ratio of thermal conductivity of two rods of different materials is $5 : 4$. The two rods of same area and same thermal resistance will have lengths is the ratio

A wall is made of two layers of thickness $1\ cm$ and $4\ cm$ and thermal conductivities $K$ and $3K$ respectively. If temperature difference for the wall is $50\ ^oC$ then temperature difference for the thin layer will be

Two rods of same length and material transfer a given amount of heat in $12\, seconds$, when they are joined end to end. But when they are joined in series, then they will transfer same heat in same conditions in ......... $\sec$