-Conduction is the process of thermal enerygy transfer by the direct contact of molecules,without any flow of the material medium.
-Conduction takes place in solids, liquids, and gases, but works best in materials that have simple molecules that are located close to each other.
-Conduction occurs when two object at different temperatures are in contact with each other. Heat flows from the warmer to the cooler object until they are both at the same temperature. Conduction is the movement of heat through a substance by the collision of molecules. At the place where the two object touch, the faster-moving molecules of the warmer object collide with the slower moving molecules of the cooler object. As they collide, the faster molecules give up some of their energy to the slower molecules. The slower molecules gain more thermal energy and collide with other molecules in the cooler object. This process continues until heat energy from the warmer object spreads throughout the cooler object. Some substances conduct heat more easily than others. Solids are better conductor than liquids and liquids are better conductor than gases. Metals are very good conductors of heat, while air is very poor conductor of heat. You experience heat transfer by conduction whenever you touch something that is hotter or colder than your skin e.g. when you wash your hands in warm or cold water
This is a thermal infrared image of a coffee cup filled with a hot liquid. Notice the rings of color showing heat traveling from the hot liquid through the metal cup. You can see this in the metal spoon as well. This is an example of conduction.
The spoon in a cup of hot coffee becomes warmer because the heat from the coffee is conducted along the spoon.
Heat being conducted along a copper rod.The heat makes the copper atoms vibrate faster. These atoms in turn make the atoms near them vibrate faster.In this way the heat energy is gradually transferred along the rod from the hot end towards the cooler end.
We can demonstrate this by coating the rod in wax and timing how long it takes the wax to melt.With a copper rod the wax will melt quicker than an iron rod because copper is a better conductor of heat.
-silver
-copper
-gold
-aluminium
-iron
-lead
Good insulators of heat:
-vacuum
-styrofoam
-air
-wood
-glass
-water
One ice cube is placed on a wood board, a second one on a black sheet of aluminium. Both bases are black and have the same shape. On Aluminium, the ice melts much quicker because Aluminium has an excellent heat conductivity.At room temperature the ice on the aluminium sheet melts much quicker than the one on wood.
This experiment demonstrates that water is a poor conductor of heat. The ice at the lower part of the test tube does not melt quickly even when the water boils at the top.
Applications of good conductors of heat:
Good conductors of heat are used in heating processes to increase the rate of energy transfer. They are also used in cooling systems to facilitate heat loss. Metals are good conductors of heat and can normally endure strong heating. They are therefore used in cooking utensils, such as pans and woks. Metals are widely used in the cooling systems of cars and power plants to enhance heat loss.
Cooling fan (left) and heat sink (right) of a computer CPU.
Applications of good insulators of heat:
Good insulators of heat are used for energy retention, or for keeping a place cold against a warm environment. Materials such as plastics and polystyrene are good insulators of heat. The handles of many cooking utensils are made of plastics for safe handling. Expanded polystyrene cups and boxes are used in fast food shops to hold hot food or drinks. Materials such as fur, cotton and feathers are often used to make clothing and quilts. We wear lightweight goose-down jackets in cold weather. Cotton quilts keep us warm at night. Fur and feathers are the natural clothing of many animals; they help animals like polar bears and seals to withstand the extreme coldness in the poles. But why are furry materials so effective for heat insulation? The secret lies not in the materials themselves but in the air they trap. Air is a very poor conductor of heat. These furry materials have many tiny air spaces within them, and can thus slow down the rate of heat loss effectively
The fur of polar bears helps to keep them warm under extreme coldness.
The handle of a cooking pan is made of plastic for safe handling.
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