Conduction is the transfer of energy (heat or electricity) from one object to another when there is direct contact between these objects. During Conduction, a molecule gains energy and starts vibrating. This energy is then transferred to the other surrounding molecules until complete transfer of energy within the body is complete.
In this article, we will understand the meaning of conduction, types of conduction, Fourier’s Law, Conduction Resistance, and Heat conduction along with the difference between conduction, convection, and radiation.
What is Conduction?
Conduction is the transfer of energy between one material particle to another when there is direct contact between the particles. There is no movement of the molecules within the particle, but the transfer of heat takes place when the molecule vibrates amongst themselves.
During Conduction, when a molecule gains heat it starts vibrating and transfers its heat to the next neighboring molecule. This process keeps on repeating until complete transfer of heat within a body takes places.
When we heat a rod, the molecules close to the heat source gains heat energy and starts vibrating. These molecules than transfer the heat to its neighbouring molecule. As a result the farther end of the rod also gets heated even when the heat is applied to the other end.
Conduction Definition
Conduction is the process of transfer of heat from a hot body to a cold body without actual movement of molecules.
In conduction, the transfer of heat takes place by direct contact of material particles. Transfer of heat through conduction is more pronounced in solids than in liquids due to less intermolecular spaces in solids (more packed molecules).
Examples of conduction
There are several examples of transfer of heat through conduction. Some of them are discussed below:
⦁ Boiling of water: When the water is poured in a vessel and heated then the molecules of water closer to the vessel are heated which transfer their heat to neighbouring molecules. Thus, the entire quantity of water is heated via conduction.
⦁ Holding an ice cube: Whenever we hold an ice cube in our hand, we get the feeling of coldness in our hands. This is because the transfer of heat through conduction takes place from our hands to ice cube.
⦁ Ironing of cloths: When the cloths are ironed, the transfer of heat takes place from iron to cloths via conduction which removes the wanted creases from cloths.
Types of Conduction
There are mainly two types of conduction of heat namely:
- Steady State Conduction
- Transient Conduction
Steady State Conduction
Steady state refers to the condition when the temperature of each section of the substance is constant. In steady state conduction the transfer of heat takes place with a constant rate.
A material in which steady-state conduction takes place is called as steady-state conductor. During this conduction, the temperature of the material remains same.
Transient Conduction
Transient Conduction is also known as non-steady conduction. It occurs when the temperature of the substance changes, i.e., the temperature of the substance is changed either from outside or inside.
During the transient conduction, the temperature change is due to the sudden entry of a new heat source within the object. In this conduction, the temperature of the substance varies within the object at a given time.
Fourier’s Law
Fourier’s Law is also known as the law of heat conduction. This law states that during the conduction of heat the negative gradient of temperature and time in which heat transfer takes place is directly propotional to area of that gradient through which heat flows.
It is mathematically represented as:
q ∝ – A (dT/dx)
q = – kA dT/dx
where,
- q= heat flux
- A= Area
- dT/dx= Temperature gradient
The gradient is negative as heat flows from hot body to cold body.
Conduction Resistance
Conduction resistance is the resistance offered by the material when the transfer of heat takes place in material. It is also called as thermal resistance. Higher the value of thermal resistance lesser will be the conductivity of the substance.
In other words, if the value of thermal resistance is high then substance will be insulator while if the value of thermal resistance is low then the substance would be a conductor.
Thermal resistance depends on many factors. Some of them are described below:
Conductivity: Conductivity is inversely proportional to conduction resistance. Higher the conductivity of the substance lesser would be the resistivity of the substance.
Area of cross-section: When the area of cross-section is larger, it offers low resistance of heat to the substance.
Length of substance: Length of the substance is directly proportional to resistivity of heat. When the length of substance is increased, resistivity also increases.
Heat Conduction
Heat conduction is the movement of heat from one object to another when they are in contact with each other. It occurs when there is a temperature difference between the two bodies. It is caused due to the movement of electrons within the body.
Coefficient of thermal conductivity of a material is factor that depicts how well a material can transfer its heat energy from one molecule to another.
Conduction in matters depends on various factors, some of them are discussed below-
Cross-section of material: Transfer of heat is directly proportional to the cross-section of the material. More the cross-section area of the material, more rapidly the conduction of heat takes place.
Length of the material: Length of a material represents the distance through which the conduction of heat takes place. It is inversely proportional to the conduction of heat, i.e., lesser the length, more rapidly the transfer of heat takes place.
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Classification of Material Based on Conductivity
Based on the conductivity of the substance, there are two types of substances:
Conductors: These are the substances which allows the heat energy to flow through them easily. They are called good conductors of heat or simply conductors. These substances offer low resistance to thermal conductivity. Some examples of conductors are- copper, aluminum, iron, graphite, etc.
Insulators: These are the substances which does not allow the heat energy to flow through them easily . They are called bad conductors of heat or simply insulators. These substances offer high resistance to thermal conductivity. Some examples of insulators are- plastic, mica, air, wood, fabrics, etc.
Read More, Conductor and Insulator
Difference Between Conduction, Convection and Radiation
Transfer of heat takes place via conduction, convection and radiation. Difference between them is listed in the table given below:
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Medium is required.
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Medium is required.
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Medium is not required, can occur in vacuum.
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Transfer of heat takes place by direct physical contact.
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Transfer of heat takes place my motion of particles.
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Transfer of heat takes place by electromagnetic radiation.
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Occurs due to difference in temperature between two substances.
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Occurs due to difference in density between two substances.
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Occurs at all bodies which have temperature above absolute zero (0K).
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It is slow process.
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It is a faster process than conduction.
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It is fastest process of all three modes.
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Path of transfer of heat is irregular.
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Path of transfer of heat is irregular.
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Path of transfer of heat is linear.
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Conduction: Frequently Asked Questions
What is Electrical Conductor?
Electrical Conductors are materials that allows electric charge to flow through it with little resistance. Electrical conductors are usually metals, such as copper, silver, etc.
What are Superconductors?
The substances in which there exists a zero resitance or infinite conductance are called superconductors. These exits at very low temperatures, which is near to absolute zero.
What is Conduction and Convection?
Conduction is the transfer of energy between one particle to another when there is direct contact between the particles whereas Convection is the transfer of heat energy from one particle to another by the movement of its constituent particles.
What are the Types of Conduction?
There are three types of conduction:
- Ionic conduction
- Electric conduction
- Heat conduction
What are Modes of Heat Transfer?
There are three modes of heat transfer- conduction, convection and radiation.
What is Conduction of Metal?
Conduction of metals is caused due to collisions between fast-moving free electrons and metal ions. Metals are good conductors of heat and electricity.
Does Gravity play any role in Transfer of Heat?
Gravity takes part only in convection only. In conduction and radiation, gravity does not play any role in heat transfer.
What is a Black Body?
A black body is a body which completely absorbs all radiation falling on it whatever be its wavelength.
What is the Difference Between Temperature and Heat?
- Heat is a form of energy which is transferred between two bodies when there is a temperature difference between them.
- Temperature is defined as a property of body which tells the degree of hotness or coldness of body with respect to another body.
What is Unit of Transfer of Heat?
Heat is measured in joules(J) and transfer of heat is measured in joule per second(J/s).
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