A wall is made of two layers of thickness $1\  cm$ and $4\  cm$ and thermal conductivities $K$ and $3K$ respectively. If temperature difference for the wall is $50\ ^oC$ then temperature difference for the thin layer will be

A body cools in a surrounding which is at a constant temperature of $\theta _0$ . Assuming that it obeys Newton's law of cooling, its temperature $\theta $ is plotted against time $t$ . Tangents are drawn to the curve at the points $A(\theta  = \theta _1)$ and $B(\theta = \theta _2)$ . These tangents meet the time-axis at angles $\alpha _1$ and $\alpha _2$ as shown in the graph then

Two large holes are cut in a metal sheet. If this is heated, distances $AB$ and $BC$, (as shown)

A black body at a high temperature $T\, K$ radiates energy at the rate $E\, watt/m^2$ ; when the temperature falls to $(T/2)\, K$ the radiated energy will be

A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using

$Assertion :$ Bodies radiate heat at all temperatures.
$Reason :$ Rate of radiation of heat is proportional to the fourth power of absolute temperature.