Various mechanisms of Heat transfer

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. Heat is a form of energy called thermal energy. It is a common experience that heat always flows from a hot to a cold object. There are many ways through which heat can be transferred. We are going to discuss these ways one after the other. Science called these mechanisms or ways; conduction, convection, and radiation.

CONDUCTION

_{A cup of tea with a spoon}
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It is our everyday experience that's when we pour hot water into an aluminum cup the handle of the cup soon feels hot to the touch. If you deep a silver spoon into a hot tea, the handle of the silver spoon very quickly feels hotter than it was before. What makes the handle to be hot was that heat has been transferred from the hot water to the spoon. The hot tea has caused the metal handle of the spoon to feels hot by the process of conduction.

In definition, heat is the process by which heat energy is transferred to a material, the average position of the particles of the material remaining the same.

When we have different temperatures at a different level of a solid, heat is normally transferred and the heat moves from the region of higher concentration to the lower region. That's from the hotter part to the cooler part.

Metallic metals like copper, aluminum, silver, iron, etc, easily conduct heat energy through them. They're the perfect transmitter of heat. On the contrary, water, air, wood, plastic, cloth, cotton, wool, cork, etc are known as non-conductors of heat. Or we can call them insulators. They do not conduct or allow heat to pass through them.
The handle of a cooking utensil is made of wood or plastic which are insulators, cooking utensil itself is made of a good conductor such as aluminum so that heat can be conducted easily through utensils but not through the handle.

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_{Cooking utensils}

Convention

Add a few drops of coloring matter for example ink, to a beaker of water. Add some aluminum powder which should sink to the bottom of the beaker. Gently heat the beaker with a small flame at the center of the base. Notice the movement of the aluminum particles. After a Time, bubbles form at the bottom of the beaker and rise.

Although practically, we can not spot the water particles but the behavior of the aluminum particles is a good indication of what is happening to the water particles too.
Eventually, all the water in the beaker will be heated up and it will boil. Although from our knowledge, what is a bad conductor of heat, yet when you heat the beaker at the bottom, the water at the top very soon gets one as you can test with a thermometer or even with your finger. From these experiments, you can see that heat was transferred from the bottom of the water to the uppermost top through the convention.

The difference between conduction and conversion is that in conduction the average position of the molecules remains the same but in convection heat is carried to the other parts of the liquid by the actual movement of the warm liquid itself.

Radiation

The third mechanism of heat transfer is radiation.
The process by which heat is transferred from a hotel to a cooler place without hitting the intervening medium is called radiation. In radiation, no material medium is needed, unlike conduction and convection which requires a material medium.

The heat from the sun reaches the Earth by radiation. When you warm yourself by the fireside the heat from the fire reaches you by radiation.

_{Radiation of the sun}
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The heat energy given out by radiation is known as radiant heat or radiant energy. Such Radiation is electromagnetic. It is called the infra-red and it travels with the velocity of light (3×10^8)