What is conduction, convection and radiation

The way we travel from one place to the other, in the same way the heat also travels from one place to the other by different modes. This process of the travelling of heat from one body to other or one place to other is called Heat Transfer.

There are different modes of heat transfer:

1. Conduction
2. Convection
3. Radiation

Generally the process of conduction takes place in solids or solid fluid interface. Where as the process of Convection takes place in the fluids such as air and water. The Radiation process does not require any material medium for their transfer.

Conduction:

We know that conduction takes place in solids or solid fluid interface.

But how ????

👉 In solids, the molecules are very close to each other. They are very closely packed such that they can't move from one place to other unlike the fluids.

Like in this figure, we can see the packaging of the molecules.

Now, what will happen if we start heating the side A ?

1.  The molecules at side A will start getting hot.
2. The molecules which are just close to the hot ones will start getting hot by absorbing the heat energy from them. " You can see there are columns of molecules." So, heat will start travelling from one molecule column to the other.
3. All this happened because the molecules were in touch with each other.
4. Slowly the molecules which are on side B will become hot

📌📌

What did just happen ?

👉 The heat got transferred from side A to side B. But we can see here that the molecules did not move. Just the heat energy was transferred to the nearby molecules.

This is the process of conduction of heat.

Let me give you another example. Suppose five students are standing in a line as shown in figure below

Suppose the first student has the ball as you can see. If the ball has to be put in the bucket, then will the first student go and put it there?

👉 Noooo !!.. the ball will be passed to 2nd 👉to 3rd 👉to 4th👉to 5th 👉 bucket.

See.. this was similar to conduction process. Wasn't it ?

Convection:

What did we just see in Conduction?

👉 The molecules were standing at their position and they were just passing on the heat to the next molecule.

But this does not happen in case of convection.

Before getting into it, let's imagine a rugby or football match. A player who has the ball runs towards the goal post. Just the same thing happens in the molecules of fluids ( air & water ). The molecule which gets the heat start rising upward and the cold molecules which tend to remain at lower positions take its place.

Let us analyse it now.

As you can observe that the molecules which were just above the burner get the heat and start rising upwards and cold molecules from side take its place. The molecules keep on rising from middle and come down from the sides until all the molecules are heated up. This process is called Convection.

Here, the heat transfer takes place by actual movement of the molecules which was not the case in conduction.

Radiation:

Conduction and convection needed molecules for the heat transfer. In conduction molecules were passing the heat on to the next adjacent molecule and on the other hand in convection the molecules carried and moved around with the heat.

Now, the radiation : It does not need any material medium for its transfer. We know that out of the earth's atmosphere every thing is vacuum. In that vacuum only, planets and satellites are there. Now, planets and satellites are solids. Few are even compact gases. But they cannot transfer the heat energy because they are not in contact with each other. For conduction also we need to molecules to be in contact. Now, the radiation comes in to picture. Radiation is a method of transfer of heat in the form of waves. It is the same way through which heat comes from sun to earth. Even when we are sitting in front of fire, we get the heat though knowing that the hot gases will rise vertically up. Then how does heat reach us that way? It is transferred through radiations.