On a winter morning,a metal surface feels colder to the touch than a wooden surface because:

Two rods are connected as shown. The rods are of the same length and same cross-sectional area. In the steady state,the temperature $(\theta)$ of the interface will be........ $^oC$

Three rods of the same dimensions have thermal conductivities $3k, 2k$ and $k$. They are arranged as shown,with their ends at $100\,^{\circ}C, 50\,^{\circ}C$ and $0\,^{\circ}C$. The temperature of their junction is

$A$ wall is made of equally thick layers $P$ and $Q$ of different materials. The thermal conductivity of $Q$ is half of that of $P$. In the steady state,if the temperature difference across the wall is $24^{\circ} C$,then the temperature difference across the layer $P$ is ............... . (in $^{\circ} C$)

Two rods with thermal conductivities $K$ and $3K$ and equal cross-sectional areas are joined as shown in the figure. Their lengths are $1 \ cm$ and $2 \ cm$,respectively. If the temperatures of the two ends of this composite rod are $0^{\circ}C$ and $100^{\circ}C$ (see figure),then the temperature $\phi$ of their interface is:

Define thermal conductivity. Also,provide its $SI$ unit and dimensional formula.