Heat Conduction

In this mechanism, heat transfer is due to vibration amplitudes of molecules & atoms present in solids.

Consider a cubicle of solid. Let us maintain one face of cube at high temperature (TH) and other opposite face at low temperature(Tc).

Due to temperature difference an amount of heat energy (Q) passes from  hot face to cold face in time 't'.

Conduction rate  Pcond (amount of energy transferred for uni time) is

Pcond = Q/t = K*A*(TH-Tc)/d;

where 'K' is coefficient of thermal conductivity, a constant for given material.
           'd' is thickness of slab
           'A' Area of slab
            't' is time of conduction

Therefore, Q= K*A(TH-Tc)*t/d

Note: i) 'K' depend on nature of material of which slab is made
         ii) A good thermal conductor has 'K' greater value.

Thermal Resistance to conduction(R-value):

This explains resisting of thermal conductivity. The R-value(thermal resistance) of a slab of thickness 'd' is defined as R=d/k. Thus material having less value of 'K' will have higher R-value and thus acts as a good thermal insulator.


i) 'R' is properly assigned to specified thickness of slab but not to material of slab.
ii) In steady state, conducting rates thru any no. of materials must be equal.
     Therefore, Pcond = A*(TH-Tc) / Σ(d/K)
iii) Heat is transferred from molecule to molecule by conduction. In this case molecules do not bodily move but simply vibrate.

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