Three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. The first and third plates are maintained at temperatures $2\,T$ and $3\,T$ respectively. The temperature of the middle (i.e. second) plate under steady state condition is
${\left( {\frac{{65}}{2}} \right)^{\frac{1}{4}}}\,T$
${\left( {\frac{{97}}{4}} \right)^{\frac{1}{4}}}\,T$
${\left( {\frac{{97}}{2}} \right)^{\frac{1}{4}}}\,T$
${\left( {97} \right)^{\frac{1}{4}}}\,T$
Heat is conducted across a composite block of two slabs of thickness $d$ and $2d$. Their thermal conductivities are $2k$ and $k$ respectively. All the heat entering the face $AB$ leaves from the face $CD$. The temperature in $^o C$ of the junction $EF$ of the two slabs is :
The power radiated by a black body is $P$ and it radiates maximum energy around the wavelength $\lambda_0$. If the temperature of the black body is now changed so that it radiates maximum energy around wavelength $\frac{3}{4}\lambda_0$, the power radiated by it will increase by a factor of
$Assertion :$ Bodies radiate heat at all temperatures.
$Reason :$ Rate of radiation of heat is proportional to the fourth power of absolute temperature.
Two rods of crossectional area $A$ and $2A$ and equal length having thermal conductivities $2K$ and $3K$ are joined in parallel, then equivalent thermal conductivity of their combination will be-
A block of metal is heated to a temperature much higher than the room temperature and allowed to cool in a room free from air currents. Which of the following curves correctly represents the rate of cooling