The original temperature of a black body is ${727^o}C.$The temperature at which this black body must be raised so as to double the total radiant energy, is ....... $K$
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Two materials having coefficients of thermal conductivity $3K$ and $K$ and thickness $d$ and $3d$, respectively, are joined to form a slab as shown in the figure. The temperatures of the outer surfaces are $\theta_2$ and $\theta_1$ respectively $\left( {\theta _2} > {\theta _1} \right)$ . The temperature at the interface is
The black body spectrum of an object $O _1$ is such that its radiant intensity (i.e. intensity per unit wavelength interval) is maximum at a wavelength of $200\,nm$. Another object $O _2$ has the maximum radiant intensity at $600\,nm$. The ratio of power emitted per unit area by source $O _1$ to that of source $O _2$ is
A rod of length $L$ and uniform cross-sectional area has varying thermal conductivity which changes linearly from $2K$ at endAto $K$ at the other end $B$. The endsA and $B$ of the rod are maintained at constant temperature $100^o C$ and $0^o C$, respectively. At steady state, the graph of temperature : $T = T(x)$ where $x =$ distance from end $A$ will be
Bottom of a lake is at $0^{\circ} C$ and atmospheric temperature is $-20^{\circ} C$. If $1 cm$ ice is formed on the surface in $24 \,h$, then time taken to form next $1 \,cm$ of ice is ......... $h$
For the figure shown, when arc $ACD$ and $ADB$ are made of same material, the heat carried between $A$ and $B$ is $H$ . If $ADB$ is replaced with another material, the heat carried becomes $2H$ . If the temperatures at $A$ and $B$ are fixed at $T_1$ and $T_2$ , what is the ratio of the new conductivity to the old one of $ADB$
Two bars of thermal conductivities $K$ and $3K$ and lengths $1\,\, cm$ and $2\,\, cm$ respectively have equal cross-sectional area, they are joined lengths wise as shown in the figure. If the temperature at the ends of this composite bar is $0\,^oC$ and $100\,^oC$ respectively (see figure), then the temperature $\varphi $ of the interface is......... $^oC$
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 following figure shows two air-filled bulbs connected by a $ U-$ tube partly filled with alcohol. What happens to the levels of alcohol in the limbs $X$ and $Y$ when an electric bulb placed midway between the bulbs is lighted
A body cools in $7$ minutes from $60^{\circ}\,C$ to $40^{\circ}\,C$. The temperature of the surrounding is $10^{\circ}\,C$. The temperature of the body after the next $7$ minutes will be