Heat and Mass Transfer
Thermal conductivity of a material may be defined as the

Quantity of heat flowing in one second through one cm cube of material when opposite faces are maintained at a temperature difference of 1°C
Quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
All of these
Heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces

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