Explain thermal conductivity and obtain an expression for
coefficient of thermal conductivity. compare it with electrical
conductivity.
Answers
Thermal conductivity :- refers to the ability of a given material to conduct/transfer heat. It is generally denoted by the symbol ‘k’.The reciprocal of this quantity is known as thermal resistivity.
Fourier’s law of thermal conduction (also known as the law of heat conduction) states that the rate at which heat is transferred through a material is proportional to the negative of the temperature gradient and is also proportional to the area through which the heat flows.
⇒ ‘k’ = q * d/(T1 - T2)
Where , q = quantity of heat passing through a unit area of the sample in unit time [W/m² ]
d = distance between two sides of the sample [m]
T1 = temperature on warmer side of the sample [K]
T2 = temperature on the colder side of the sample [K
The quantity of transferred heat q is given by:
⇒ q = Q/A [W/m² ]
Where,
Q = is quantity of heat passing through a base area of the sample [W]
A = base area of the sample [m²]
Thermal conductivity is the propensity for any material to transfer heat from one point to another. Of course for heat to "flow," it is necessary for a difference of temperature to exist within a continuous section of the material. Thermal conductivity is analogous to electrical conductivity. Similarly, thermal resistance is the inverse of thermal conductivity as electrical resistance is the inverse of electrical conductivity.
Coefficient of thermal conductivity also known as coefficient of thermal expansion is the rate at which a material will grow in length with an increase in temperature. Most material grow in a fairly linear fashion, particularly within a defined range of temperatures. A positive coefficient of expansion indicates that the material gets longer as its temperature increases. Most metals are like that. Ice is a well-known example of a negative coefficient of expansion, since it contracts in length with increasing temperature.