[Physics Class Notes] on Thermal Conductivity of Metals Pdf for Exam

Conductivity of Metals

Conduction is an important concept in Physics. It is one of the three concepts by which heat and energy can be transferred from one place to the other within a material or from one material to another. Conduction occurs by direct contact whereas Convection occurs by movement or flow of heat. Radiation on the other hand occurs with the help of electromagnetic waves. Conduction mostly occurs in metals and the conductivity of metals is different from one another. When it comes to the best metal for thermal conductivity, ideally it is Silver but Copper is used instead. The reason for it is that Silver is too expensive and is infeasible to use. Copper, on the other hand, is available in abundance, is affordable, and can be used in any application.

Law of Conduction

A list containing the conductivity of various metals is used to compare and accordingly use metal for a specific purpose. Calculating the thermal conductivity of the metal rod was one of the initial and important experiments that were carried out to measure the conductivity of metals.

The law of conduction or the Fourier’s law states that the time required for heat transfer through metal is proportional to the negative gradient in the area and temperature. This law is applicable in two forms; differential form and integral form. 

Various calculations can be made to measure the transfer of heat. Heat flux for instance is the amount of heat flow that occurs per unit area. Similarly, the opposite of thermal conductivity, which is thermal resistivity, can also be calculated. 

Thermal resistivity is the ability of a material to not conduct heat. This property is present in materials that do not conduct heat. They are used as insulators. Some of them are rubber, fabric, cork, ceramic, styrofoam, etc.

Heat transfer is bound to occur when two materials of different temperatures come in contact with each other. Thermal insulation is done to minimize the heat that is transferred from one material to the other. This process also depends on the product density and the specific heat capacity of the insulating material used.

Thermal Conductivity of Metals: Uses

Based on their rate of conduction, metals are classified and used for particular applications. If a metal has high thermal conductivity, then it is used in heat sink applications. On the other hand, if the metal has low thermal conductivity, then it is used in thermal insulation applications. 

Insulation acts against heat transfer whereas heat sink favors it. If you consider some metals like steel and copper then, the thermal conductivity of steel and copper is 45 W/m-K i.e. 45 Watts per meter-Kelvin and 385 W/m-K i.e. 385 Watts per meter-Kelvin respectively.

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Solved Example

Question 1:  Consider a window of width 1.3m and height 1.7m, having a thickness of 6.3mm and a thermal conductivity value of 0.28 W/m/degree C. The temperature inside the house is 22 degrees Celsius and that outside the house -5 degrees Celsius.  Calculate the rate of heat transfer.

Answer: Surface Area of the window = length x breadth

    = (1.3 x 1.7) meter square

= 2.21 meter square

The thickness of the window = 6.3 mm

= 0.0063 m

Rate of heat transfer = (Thermal conductivity) x (Surface area) x (Difference of the temperatures) / (Thickness of the window)

= (0.28 W/m/degree C) x (2.21 meter square) x (22-(-5) degrees C) / (0.0063 m)

          ~ 2652 W

The rate of heat transfer for the given example is 2652 W.

Fun Fact

Did you know that besides metals, gases can be conductors of heat too? Yes, that’s right. In the entire periodic table, metals and gases are the two categories of elements that can conduct heat. Most of the metals and some other elements are conductors of electricity as well. Gases, however, do not conduct electricity.

Even though they can conduct heat, their rate of conductivity is much less than the rate of conductivity of metals. Due to this, gases are instead used as insulators. Thermal insulation or resistivity is the property of not being able to conduct heat. 

Materials such as rubber, wood, plastic, glass, etc. are used as insulators. They work opposite to the thermal conductivity of metals.