Colour of shining bright star is an indication of its
AIIMS 2001, Easy
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(c)According to Wein’s displacement law.
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A very thin metallic shell of radius $r$ is heated to temperature $T$ and then allowed to cool. The rate of cooling of shell is proportional to ........
A black body radiates heat energy at the rate of $2\times10^5\, J/sm^2$ at temp. of $127\,^oC$. The temp of black body at which rate becomes $32\times10^5\, J/s-m^2%$ is ....... $^oC$
The heat is flowing through a rod of length $50 cm$ and area of cross-section $5c{m^2}$. Its ends are respectively at ${25^o}C$ and ${125^o}C$. The coefficient of thermal conductivity of the material of the rod is $0.092 kcal/m×s×^\circ C$. The temperature gradient in the rod is
A cup of coffee cools from $90^{\circ} \mathrm{C}$ to $80^{\circ} \mathrm{C}$ in $\mathrm{t}$ minutes, when the room temperature is $20^{\circ} \mathrm{C}$. The time taken by a similar cup of coffee to cool from $80^{\circ} \mathrm{C}$ to $60^{\circ} \mathrm{C}$ at a room temperature same at $20^{\circ} \mathrm{C}$ is :
A black body radiates at the rate of $W$ watts at a temperature $T$ . If the temperature of the body is reduced to $T/3$ , it will radiate at the rate of (in Watts)
Two spheres of the same material have radii $1\; m$ and $4\; m$ and temperatures $4000 \;K$ and $2000 \;K$ respectively. The ratio of the energy radiated per second by the first sphere to that by the second is