(a)Natural convection arises due to difference of density at two places and is a consequence of gravity.
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Assume that Solar constant is $1.4 \,kW / m ^2$, radius of sun is $7 \times 10^5 \,km$ and the distance of earth from centre of sun is $1.5 \times 10^{8} \,km$. Stefan's constant is $5.67 \times 10^{-6} \,Wm ^{-2} K ^{-4}$, find the approximate temperature of sun ....... $K$
The end $A$ of a rod $AB$ of length $1\,m$ is maintained at $80\,^oC$ and the end $B$ at $0\,^oC.$ The temperature at a distance of $60\,\,c.m.$ from the end $A$ is......... $^oC$
The 'Kangri' is an earthen pot used to stay warm in Kashmir during the winter months. Assume that the 'Kangri' is spherical and of surface area $7 \times 10^{-2} \,m ^{2}$. It contains $300 g$ of a mixture of coal, wood and leaves with calorific value of $30 \,kJ / g$ (and provides heat with $10 \%$ efficiency). The surface temperature of the 'Kangri' is $60^{\circ} C$ and the room temperature is $0^{\circ} C$. Then, a reasonable estimate for the duration $t$ (in h) that the 'Kangri' heat will last is (take the 'Kangri' to be a black body)
There is a rough black spot on a polished metallic plate. It is heated upto $1400 K$ approximately and then at once taken in a dark room. Which of the following statements is true
A solid cylinder of length $L$ and radius $r$ is heat upto same temperature as that of a cube of edge length $a$. If both have same material, volume and allowed to cool under similar conditions, then ratio of amount of radiations radiated will be (Neglect radiation emitted from flat surfaces of the cylinder)
Wein's constant is $2892 \times {10^{ - 6}}$$MKS$ unit and the value of ${\lambda _m}$ from moon is $14.46$ microns. What is the surface temperature of moon ...... $K$
The temperatures of two bodies $A$ and $B$ are respectively ${727^o}C$ and ${327^o}C$. The ratio ${H_A}:{H_B}$ of the rates of heat radiated by them is