d (d) The polished surface reflects all the radiation.
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Two spherical stars $A$ and $B$ emit blackbody radiation. The radius of $A$ is $400$ times that of $B$ and $A$ emits $10^4$ times the power emitted from $B$. The ratio $\left(\lambda_A / \lambda_B\right)$ of their wavelengths $\lambda_A$ and $\lambda_B$ at which the peaks occur in their respective radiation curves is
Wires $A$ and $B$ have identical lengths and have circular cross-sections. The radius of $A$ is twice the radius of $B$ $i.e.$ ${r_A} = 2{r_B}$. For a given temperature difference between the two ends, both wires conduct heat at the same rate. The relation between the thermal conductivities is given by
A cup of tea cools from $65.5^o C to 62.5 ^o C$ in one minute in a room of $22.5 ^o C$. How long will the same cup of tea take, in.............. minutes, to cool from $46.50^o C to 40.5 ^o C$ in the same room ? (choose nearest value)
A cylinder of radius $R$ is surrounded by a cylindrical shell of inner radius $R$ and outer radius $2R$. The thermal conductivity of the material of the inner cylinder is $K_1$ and that of the outer cylinder is $K_2$. Assuming no loss of heat, the effective thermal conductivity of the system for heat flowing along the length of the cylinder is
There are two spherical balls $A$ and $B$ of the same material with same surface, but the diameter of $A$ is half that of $B$. If $A$ and $B$ are heated to the same temperature and then allowed to cool, then
A $5cm$ thick ice block is there on the surface of water in a lake. The temperature of air is $-10°C$ ; how much time it will take to double the thickness of the block ...... hour ($L = 80 cal/g, Kicc = 0.004 Erg/s-k, dice = 0.92 g cm^{-3}$)
A planet of radius $R_{p}$ is revolving around a star of radius $R^{*}$, which is at temperature $T^{*}$. The distance between the star and the planet is $d$. If the planet's temperature is $f T^{*}$, then $f$ is proportional to
hree rods of same dimensions are arranged as shown in figure they have thermal conductivities ${K_1},{K_2}$ and${K_3}$ The points $P$ and $Q$ are maintained at different temperatures for the heat to flow at the same rate along $PRQ$ and $PQ$ then which of the following option is correct