Part 2! CONVECTION

Have ever you had a hot pot meal in the winter? You may notice that the food keeps moving up and down in the water even when the temperature is well below that of boiling. This indicates that bulk movement of water exists when it is being heated. In fact, this movement of water, known as convection, serves as an effective way of heat transfer, especially when the rate of heating is high.

WHAT IS CONVECTION?
-Convection is the transfer of thermal energy by means of currents in a fluid( liguids or gases)

-When a fluid is heated, the particles in the volume of the fluid that is heated most (closest to the heat source) becomes more energetic and move faster and move apart from each other, lowering the density. The hotter and less dense part of the fluid thus rises. On the other hand, cooler and denser fluid sinks. As a result, heat is transferred upwards by the rising fluid. The rising of the hotter portion and the sinking of the cooler portion of the fluid form a convection current.






When a beaker of water is heated from below, a convection current is set up.






Convection of water observed with a dissolving crystal





Convection of water observed in a transparent pot. Tiny food particles are seen to move up and down.





The convection of air drives the smoke of a burning candle upwards.




-Convection does not take place in solids; it only takes place in fluids.
This is because convection involves the bulk movement of the fluids which carry thermal energy with them. For solids, the thermal energy is transferred from one particle to another through vibrations, without any bulk movement of the particles themselves.