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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 ........
The energy spectrum of a black body exhibits a maximum around a wavelength ${\lambda _o}.$ The temperature of the black body is now changed such that the energy is maximum around a wavelength $\frac{{3{\lambda _o}}}{4}$.The power radiated by the black body will now increase by a factor of
The maximum wavelength of radiation emitted at $2000\;K$is $4\mu m$. What will be the maximum wavelength of radiation emitted at $2400\,K$ is ...... $\mu m$
For a black body at temperature $727^{\circ} C$, its radiating power is $60\; watt$ and temperature of surrounding is $227^{\circ} C$. If temperature of black body is changed to $1227^{\circ} C$ then its radiating power will be ..... $watt$
The only possibility of heat flow in a thermos flask is through its cork which is $75 cm^2$ in area and $5 cm$ thick. Its thermal conductivity is $0.0075 cal/cmsec^oC$. The outside temperature is$ 40^oC$ and latent heat of ice is $80 cal g^{-1}$. Time taken by $500 g$ of ice at $0^oC$ in the flask to melt into water at $0^oC$ is ....... $hr$
The rate of loss of heat from a body cooling under conditions of forced convection is proportional to its $(A)$ heat capacity $(B)$ surface area $(C)$ absolute temperature $(D)$ excess of temperature over that of surrounding : state if
If the temperature of the sun were to be increased from $T$ to $2T$ and its radius from $R$ to $2R$ , then the ratio of the radiant energy received on the earth to what it was previously will be
Three rods of Copper, Brass and Steel are welded together to form a $Y$ shaped structure. Area of cross - section of each rod $= 4\ cm^2$ . End of copper rod is maintained at $100^o C $ where as ends ofbrass and steel are kept at $0^o C$. Lengths of the copper, brass and steel rods are $46, 13$ and $12\ cms$ respectively. The rods are thermally insulated from surroundings excepts at ends. Thermal conductivities of copper, brass and steel are $0.92, 0.26$ and $0.12\ CGS$ units respectively. Rate ofheat flow through copper rod is ....... $cal\, s^{-1}$
Two rods having thermal conductivity in the ratio of $5 : 3$ having equal lengths and equal cross-sectional area are joined by face to face. If the temperature of the free end of the first rod is $100°C$ and free end of the second rod is $20°C$ . Then temperature of the junction is...... $^oC$
The temperature of a body falls from ${50^o}C$to ${40^o}C$ in $10$ minutes. If the temperature of the surroundings is ${20^o}C$ Then temperature of the body after another $10$ minutes will be ........ $^oC$