Conduction - Transfer of Energy for JEE

Conduction is the process of transferring energy by means of the motion of particles in contact with one another, and it is a recognizable phenomenon in all the states of matter (solids, liquids and gases). Materials allowing conduction are referred to as conductors. On the basis of energy transferred during this process, conduction is classified as heat, electrical, and sounds conduction.

It must be noted that during transmission of heat energy from one substance to another, there is no alternation in the state of matter, as the particles transfer energy by vibrating at their original positions only. In electrical conduction, the transfer of charge occurs through free electrons and ions inside the conductor, and the current is allowed to pass. The conduction of heat and electricity can be noticed in day-to-day events. Let’s get deeper into the topic.

List of Properties of Conduction

• Thermal energy is transferred between materials by direct contact.

• The transfer of heat in case of conduction is at a low speed. For example, the hotter end of a heated metal rod transmits the heat to the cooler end slowly.

• The conduction of heat only happens through a hot material, that is, the transfer of heat will occur when a material is heated.

• Heat transfer starts due to the temperature difference between the materials.

Units of Conduction

For thermal conductivity, the SI unit is watts/meter-kelvin \[\left( \dfrac{W}{mK} \right)\], or \[\left( \dfrac{W}{cmK} \right)\],

And thermal conductivity, \[K=\dfrac{QL}{A\Delta T}\]

Where,

Q = Quantity of heat transfer through any material in $\left(\dfrac{J}{s}\right)$ or (W)

A = Area of the body in (m2), and

\[\Delta T=\] Difference in the temperature in \[({}^\circ K)\]

In case of electric conduction, conductivity \[(\sigma )\] which is inversely proportional to resistivity \[(\rho )\], SI unit is siemens/meter or $(\dfrac{S}{m})$.

And \[\sigma =\dfrac{1}{\rho }\]

Various other units of conduction include $\left(\dfrac{mho}{m}\right)$, BTU and so on.

Types of Conduction

There are three types of conduction that are to be discussed.

• Thermal conduction or Heat conduction

• Electrical Conduction

• Sound or Acoustic Conduction

Let’s go through each one in detail.

1. Thermal Conduction or Heat Conduction:

The energy transmission from a hotter material to a colder material, when both are in contact with each other, is referred to as thermal conduction. Conduction of energy occurs inside an object at fixed position due to temperature difference in the adjacent material in contact with each other.

Movement of energy may be fast or gradual depending on the type of material and is subject to its various properties. One significant property is temperature gradient which is defined as the way and rate in which a change in the temperature occurs from one point to another. Copper and diamonds are good thermal conductors.

Thermal conduction can be explained by conduction of heat in an iron rod which is being heated at one of its ends. Heat energy provided to one end travels to the other end due to temperature difference. Conduction is possible due to vibration of atoms at the heated end which slowly transfers the heat and distributes the heat energy to the other end and the rod attains thermal equilibrium.

Heat conduction in iron rod heated at one end.

2. Electrical Conduction:

It refers to the movement of electrically charged molecules through a particular medium, as the electricity passes through the power lines. The strength of the electric field is directly proportional to the density of the material and the density of the material is a major criterion to decide the conductivity of a material. Metals are good conductors of electricity, as they have almost negligible resistance towards electric current. On the other hand, insulators offer maximum resistance towards the flow of electric current.

Copper and silver are good examples of conducting material, but copper is a preferred material for electric wires because it is a better conductor of electricity as compared to silver, and is also economically efficient. Structure of the materials plays a major role in determining the bonding of electrons and the release of atoms with ease. Superconductors are the ones when cooled closely to absolute zero temperature, possess zero electrical resistance, and permit the incoming electric charges to pass without any loss in energy.

3. Sound or Acoustic Conduction:

It is the transportation of sound waves through a medium, similar to vibrations from loud music which can be felt at the other side of the wall. Sound is generated due to vibration and causes the atoms inside the matter to vibrate and conduct sound through the material.

Law’s Related to Conduction

1. Ohm’s Law depicts the relationship between voltage (V), current (I) and resistance (R) and states that the voltage is equal to the product of current and the resistance in the circuit.

i.e. V=IR

2. Fourier's Law states that the thermal energy transmits from warmer materials to the cooler ones.

\[q=-k\triangledown~T\]

Where,

q= Rate of heat conduction,

k= Thermal conductivity of the material,

$\triangledown~T=$ Difference in temperature throughout the material,

List of Formulae

Conclusion

The conduction, in general, is the transportation of anything inside a material. The conduction is broadly classified into three types; heat, electric and sound conduction. Ohm’s law and Fourier’s law are two main laws associated with conduction.

Conduction uses can be noticed in heating pads, utensils made of metals for faster cooking, electric wires made of copper for better electric flow, and sonic insulators to prevent the sound entering the walls (sound proofing). In the end of this topic we got the information about conduction, its type and some important formulas related to it.