## Grade 7  |   Science  |   Heat Transfer, Heat, Olympiad, CBSE, ICSE, SOF, ITO

`Heat transfer`
As we have discussed earlier that heat is a form of energy which is transferred from one body to another body. The temperature variation of the two bodies determines the flow of heat.

Heat transfer takes place by the three modes-

1. Conduction

2. Convection

Conduction- This mode involves the transfer of heat from particle to particle without any movement of the particles at all. For example-

If you heat a metal spoon from its tip, slowly the handle will become hot as the heat has been transferred from the tip to the other end through conduction only.

All the solids are heated by conduction where no movement of the particles can take place.

When you place your hand on ice it becomes cold due to conduction only as heat from your hand has been transferred to the cold surface of the ice.

Convection- In this mode, the heat is transferred from one part of a medium to another part of the medium by the actual movement of the heated particles of the respective medium.

All the fluids (liquids and gases) are heated up by convection.

Convection is also responsible for the formation of land and sea breeze.

As you know during the daytime, the heat from the sun reaches the land and seawater on earth. As the land gets heated up faster than the sea water, the air above the land also gets heated up and becomes lighter. This lighter air starts rising up. Now the cooler air over the sea water lives towards land to fill the space. Hence, the sea breeze is created.

Now at night, the land loses its heat faster than the sea water. The air above the sea water is warmer and it rises up. So in the night, the air from the land blows towards the sea to fill the space. This is what we refer to a land breeze.

Room ventilation occurs out to convection only as the warm and impure air inside the room is continuously replaced by fresh air from the outside. Air becomes warm due to breathing and cooking in the kitchen which causes it to rise up and passes out from the ventilators. Now to fill the space cold and fresh air from outside comes inside from the doors and windows.

Earthquakes- As we know there the presence of magma between the earth's crust and core which exists in the molten state. Due to the large temperature difference between the cryt and the core, conventional currents are generated in the magma which results in immense pressure under the land masses. Sometimes, this pressure causes the sliding of some parts of land masses causing the earthquakes.

Oceanic Currents-  The oceanic currents arise due to the temperature difference as the water on the surface of the ocean gets heated due to the sun 's direct rays whereas water near the poles is cold. This causes the movement of the surface water from the equatorial region to the polar region and the water below the surface move from polar region to the equatorial region. This results in the formation of Oceanic Currents which helps to maintain the temperature of the ocean.

Radiation- It is a mode of heat transfer from the source to the receiver without any actual movement of the source or receiver and even without any heating of the intervening medium.
The heat transfer through the means of radiation requires no medium.
A common example of this is the warmth we receive from the sun. Another example is the heat we receive from the fire. The greenhouse works on this phenomena only and heating of a room by an electric heater are also because of radiation.