Thermal Energy

THERMAL ENERGY

Energy constitutes a very important aspect of our daily activities that we often need to transfer it from one point to another.

We have talked a lot about energy in this post. Energy is the mainspring of all life and of all the activities of man-kind. We have seen that the sun is the primary source of all energy available in the world and that this energy from the sun reaches us in the form of light and heat. We have also seen that energy can take different forms. We saw how one form of energy can be converted to another form. We will consider how energy is transferred from one place to another.
Specifically, we will be considering the transfer of heat energy.

TRANSFER OF HEAT ENERGY

How does heat travel from one place to another? We have already come across one way and that is the way heat gets to us from the sun. We stated that the heat from the sun travels by waves through space to us on Earth.

This method of heat transfer from the sun through space is called radiation. There are other ways in which heat travels. These are conduction and convection.

CONDUCTION

Hold a thick piece of copper wire in a bunsen flame. Can you continue to hold it for long?

The end of the wire which is not in the flame very quickly becomes hot. How does the heat get along the wire? The only way in which this can happen is for the heat to be passed on from one particle to the next until it reaches the far end of the wire. We say that heat has been conducted along the wire, and the process is called conduction.

Heat flows from a hot body to a cold body by itself. If you think for a minute, you will see why this is so. Heat is a form of energy. A hot body has energy stored up in it; that is potential energy. The only way in which a body with potential energy can loose it is by letting it pass to a body which has energy at a lower level. So, a hot body must loose heat energy to a cooler one.

Heat a pyrex test-tube half filled with water, by applying the flame near the middle of the tube. What happens to the water after some time? Touch the bottom of the tube.
How hot is it? What can you deduce from your observation about the conduction of heat by water?

Good and bad conductors

found that heat from one end of the rod was transferred to the other end without any movement of the particles of the rod. This method of heat transfer (conduction) occurs mostly in metals. Some substances conduct heat more easily than others. Good conductors are substances which conduct heat readily. All metals are good conductors of heat. Bad conductors are substances which do not conduct readily. Liquids and gases are bad conductors of heat. Water is an example of bad conductor.

CONVECTION

Use a piece of glass tubing to drop a crystal of potassiu tetraoxomanganate(VIl) on one side of a beaker full water. Heat the beaker under the crystal.

What do you observe? Eventually, all the water in the beaker will be heated up and it will boil. We have already found out that water is a bad conductor of heat. Yet, when you heat a beaker of water at the bottom, the water at the top very soon gets warm as you can test with your finger. How has the heat been transferred from the bottom of the beaker to the top?

The heat flows this time from the bottom to the top by the actual movement of the liquid molecules. This transfer of heat by the movement of liquid molecules is called convection.

The purple colour of the potassium tetraoxo-manganate (VII) shows the convection current clearly. Why should the liquid move like this when it is heated?

As the water is heated, molecules acquire heat energy, and move further apart. The hot liquid therefore becomes less dense than the colder liquid above. The molecules from the bottom rise to the top carrying the heat energy with them. The molecules from above sink to take the place of the risen molecules, and they in turn are heated and the cycle continues until the water boils.

RADIATION

We have already dealt with this method of heat transfer when we discussed the way in which heat gets to us from the sun. We also did some experiments to find out about it. Here is one more experiment to remind you about radiation.

How do we know? Nor did it travel by convection. How do we know?

This method of heat transfer which does not involve any material between the source of the heat and the receiver is called radiation. The heat is transferred by means of waves.

 

Feel free to drop your comment below ⬇️

About The Author

Leave a Reply

Your email address will not be published. Required fields are marked *