Find effective thermal resistance between $A$ & $B$ of cube made up of $12$ rods of same dimensions and shown given thermal conductivity. [ $l =$ length of rod, $a =$ cross section area of rod]

Two thin metallic spherical shells of radii ${r}_{1}$ and ${r}_{2}$ $\left({r}_{1}<{r}_{2}\right)$ are placed with their centres coinciding. A material of thermal conductivity ${K}$ is filled in the space between the shells. The inner shell is maintained at temperature $\theta_{1}$ and the outer shell at temperature $\theta_{2}\left(\theta_{1}<\theta_{2}\right)$. The rate at which heat flows radially through the material is :-

Three identical rods have been joined at a junction to make it a $Y$ shape structure. If two free ends are maintained at $90\,^oC$ and the third end is at $30\,^oC$ , then what is the junction temperature $\theta $ ?……… $^oC$

Select correct statement related to heat …….

A composite block is made of slabs $A, B, C, D$ and $E$ of different thermal conductivities (given in terms of a constant $K$ ) and sizes (given in terms of length, $L$ ) as shown in the figure. All slabs are of same width. Heat $'Q'$ flows only from left to right through the blocks. Then in steady state $Image$

$(A)$ heat flow through $A$ and $E$ slabs are same.

$(B)$ heat flow through slab $E$ is maximum.

$(C)$ temperature difference across slab $E$ is smallest.

$(D)$ heat flow through $C =$ heat flow through $B +$ heat flow through $D$.