As you increase the temperature, the electrons, which are a cold Fermi gas, get more excited. Only a thin skin of electrons around the Fermi energy, of width kT, can do anything at all, like conduct heat. As the temperature increases, the electrons can conduct more heat.
The heat conductivity of electrons is greater than the heat conductivity of phonons, and together these account for the entire thermal conductivity. What is going on is that as the temperature goes up, the higher thermal conductivity electrons are carrying a larger fraction of the heat, and this makes the thermal conductivity go down.
In the absence of electronic thermal conductivity, for an insulating material, the thermal conductivity would go down with temperature, and this is also true for the thermal conductivity of just the phonons in the metal. But the electron contribution leads to this otherwise paradoxical effect.
It always helps to remember that a metal is never classical, the electrons are always quantum. A metal is a like a gigantic chemical bond involving all the atoms in a metal nonlocally, this is the conduction band, and the shared electrons have classically paradoxical properties. This is why the Drude model is wrong and the Fermi model is right.
Typically meat at the usual oven temperature of 350 F takes about 20 minutes per
pound. The objective is to get the interior of the roast cooked which means getting it
up to between 160 F and 170 F.
In Short, you are using an convection oven at 350 degrees to raise the temperature
of the meat from around 70 F to 170 F, a rise of 100 F in N minutes.
If the oven is only at 200 F, does it make sense that it will take a lot longer
to raise the temperature of the meat to 160 F to 170 F.
350 - 70 = 280
200 - 70 = 130
280 / 100 = 2.8
130 / 100 = 1.3
2.8/1.3 = 2.154 Times as long. so 43 minutes per pound.
I would use less than this number though, as it is impossible to
fix when it is overcooked.
Best Answer
They basically measure the intensity of the infrared blackbody radiation in some wavelength region and calculate the temperature needed to give that intensity according to Planck's law.