Hello friends, today we are learning about heat and the transfer of heat. In science, heat is a form of energy. It’s also known as thermal energy. It is the sum of the kinetic energy of atoms or molecules of any particularly given substance.
In thermodynamics, heat is energy that is moved between two things when one of them has a higher temperature than the other.
Heat always flows from the hotter body to the colder body.
Here we will be learning the various ways of heat transfer, like conduction, convection, and radiation.
Let’s understand the conduction by a simple activity. We need some materials like a copper rod, small nails, a candle, a matchbox and a wooden stand. Fix the nails on the copper rod with the help of the candle wax as shown. Maintain a distance of about 2 centimetres between two nails. Insert the other end of the copper rod into the paper roll as shown. Adjust the height of the candle accordingly to the height of the wooden stand. Light the candle and place it under one end of the copper rod so that this end will get heat from the candle flame. Observe some time and see what happens to the nails. After a few seconds, the first nail falls down as you continue to provide heat to the copper rod. After some time, the second nail falls down, and after that, the subsequent nails fall down as well. If you observe carefully, you will notice that the nail nearest to the candle flame falls down first, then the second nail, and so on.
When we provide heat to one end of the copper rod, the wax used to fix the nails to the copper rod melts down and hence the nails fall off. The copper rod gets heat from the candle, and this heat transfers from the hotter end of the copper rod to the colder end of the copper rod, hence the nails fall down sequentially from the copper rod. This process of heat transfer is known as the conduction of heat. In conduction, the transfer of heat from one atom to another is accomplished by direct contact with the atoms of a copper rod.
Now let’s understand another method of heat transfer. It’s known as the "convection method." Take a small glass bottle and tie the thread to the neck of the bottle, then put a few drops of ink or food colour in it. Fill this glass bottle with hot water. Slowly insert the glass bottle into the container using a thread and observe what happens inside. You can see beautiful clouds of coloured water coming from the glass bottle. Why is it happening? The density of the hot water is less than the density of the cold water. When we submerge the hot water bottle in cold water, due to the lower density of the hot water, it goes towards the upper side of the cold water container. Here, with the help of colour, you can see the path of the hot water. This process of heat transfer is known as convection. In this convection process of heat transfer, the movement of heat by a fluid such as water or air is convective. You can make some changes to the experiment. Instead of using a single bottle, you can use three bottles and repeat the above activity. If you fill three bottles with three different colours, then you will see different colours coming from the bottles. After some time, when the temperature of the water inside the bottle and outside the bottle gets equalized, you will not find the colourful clouds in the water tank.
Now let's understand one more method of the transfer of heat. It's known as radiation. Here we are using the radiometer that we got from the market.
A radiometer is a device that measures the power of electromagnetic radiation.
In this radiometer, the vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity. Here you will find heat transfer without any medium. This type of heat transfer is known as radiation.
Here you must observe the transfer of heat by electromagnetic waves. This type of heat transfer is known as radiation.
I hope you enjoyed the above activities involving heat and heat transfer. Some of these activities you can easily perform in your home. Please do all the above activities under adult supervision. Thank you very much.
Team: Prof. Harinath Chakrapani, Dr Sourabh Dube, Dr Aparna Deshpande, Shubhangi Wankhede, Ashok Rupner, Dr Neeraja Dashaputre, Dr Chaitanya Mungi, Ankish Tirpude, Shraddha Bhurkunde, Dinesh Turkar, Pradnya Pujari, Sakhee Bhure, Dr Apurva Barve, Dr Asim Auti, Shanti Pise, Rohit Piwal and Science media centre team of IISER Pune.