A metallic sphere cools from $50^{\circ} C$ to $40^{\circ} C$ in $300 \,s.$ If atmospheric temperature around is $20^{\circ} C ,$ then the sphere's temperature after the next $5$ minutes will be close to$.....C$
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If the sun’s surface radiates heat at $6.3 \times {10^7}W{m^{ - 2}}$. Calculate the temperature of the sun assuming it to be a black body $(\sigma = 5.7 \times {10^{ - 8}}W{m^{ - 2}}{K^{ - 4}})$
Two spheres made of same material have radii in the ratio $1: 2$ Both are at same temperature. Ratio of heat radiation energy emitted per second by them is
Hot water cools from ${60^o}C$ to ${50^o}C$ in the first $10$ minutes and to ${42^o}C$ in the next $10$ minutes. The temperature of the surrounding is ......... $^oC$
The two ends of a metal rod are maintained at temperatures $100 ^o C$ and $110^o C$. The rate of heat flow in the rod is found to be $4.0\ J/s$. If the ends are maintained at temperatures $200^o\ C$ and $210^o\ C$, the rate of heat flow will be.... $J/s$
Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in $20$ minutes and $40$ minutes respectively. The ratio of thermal conductivities of the materials is
A metal rod of length $2\, m$ has cross-sectional areas $2A$ and $A$ as shown in the following figure. The two ends are maintained at temperatures $100\,^oC$ and $70\,^oC$. The temperature of middle point $C$ is ........ $^oC$
A body takes $4$ minutes to cool from ${100^o}C$ to ${70^o}C$. To cool from ${70^o}C$ to ${40^o}C$ it will take ........ $\min.$ (room temperature is ${15^o}C$)
A cylindrical rod having temperature ${T_1}$ and ${T_2}$ at its ends. The rate of flow of heat is ${Q_1}$ $cal/sec$. If all the linear dimensions are doubled keeping temperature constant then rate of flow of heat ${Q_2}$ will be