Heat Transfer Questions

Three identical heat conducting rods are connected in series as shown in the figure. The rods on the sides have thermal conductivity $2K$ while that in the middle has thermal conductivity $K$. The left end of the combination is maintained at temperature $3T$ and the right end at $T$. The rods are thermally insulated from outside. In steady state, temperature at the left junction is $T_1$ and that at the right junction is $T_2$. The ratio $T_1/T_2$ is:

The two ends of a rod of length $L$ and a uniform cross-sectional area $A$ are kept at two temperatures $T_1$ and $T_2$ ($T_1>T_2$). The rate of heat transfer, $\frac{dQ}{dt}$, through the rod in a steady state is given by:

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