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$r T$
B$\frac{1}{r}$
C$r^2$
D$r^0$
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D$r^0$
d (d)
Rate of cooling depends on temperature of body, surrounding temperature, not on radius.
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Two plates $A$ and $B$ have thermal conductivities $84\,Wm ^{-1}\,K ^{-1}$ and $126\,Wm ^{-1}\,K ^{-1}$ respectively. They have same surface area and same thickness. They are placed in contact along their surfaces. If the temperatures of the outer surfaces of $A$ and $B$ are kept at $100^{\circ}\,C$ and $0{ }^{\circ}\,C$ respectively, then the temperature of the surface of contact in steady state is $..........\,{ }^{\circ} C$.
The three rods shown in figure have identical dimensions. Heat flows from the hot end at a rate of $40 \,W$ in the arrangement $(a)$. Find the rates of heat flow when the rods are joined as in arrangement $(b)$ is ......... $W$ (Assume $K_al=200 \,W / m ^{\circ} C$ and $\left.K_{c u}=400 \,W / m ^{\circ} C \right)$
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 $30$ minutes. The ratio of their thermal conductivities will be
A constant potential difference is applied to the ends of a graphite rod, whose resistance decreases with a rise of temperature. The rod can be $(1)$ covered with asbestos or $(2)$ left open to atmosphere. Answer for steady state.
The absolute temperatures of two black bodies are $2000 K$ and $3000 K$ respectively. The ratio of wavelengths corresponding to maximum emission of radiation by them will be