Explain the Transmission of Heat

Transmission of heat (movement of heat from the hotter item to the colder item) can be brought about three ways: by conduction, convection, and radiation.

Conduction takes place when two objects touch. While you place one end of a bar of metal in the flame of a bunsen burner, heat is conducted from the end in the flame to the end you are holding. (therefore the recommendation that you wear an oven mitt if you try this experiment.) While two materials are in direct contact, such as two parts of the same metal bar, then conduction can take place. Materials that willingly conduct heat are termed as good conductors of heat. Metals are the best heat conductors. It is simple for the atoms or molecules of metal to transfer their jiggling energy to atoms or molecules which are nearby. A material that slows down the conduction of heat is known as a good insulator. Wood, cork, wool, paper and styrofoam are all poor conductors of heat, and hence are good insulators.

Convection occurs when the heated substance itself moves. When the layer of water along the bottom of the spaghetti pot becomes hot from the stove, this layer of water expands and these hotter (having more jiggle energy) molecules rise letting the cooler water above them move downward to be heated. Convection occurs in all unevenly heated liquids and gases, creating convection currents. Convection currents in our Earth's atmosphere are the main cause of weather!

Radiation is the only type of heat transfer that can occur in empty space, such as in outer space. Any energy transferred by this method is called radiant energy. All radiant energy is in the form of electromagnetic waves. The electromagnetic waves from lower energy to higher energy are: radio waves, then microwaves, infrared, visible, ultraviolet, X rays and gamma rays. All objects give off a mixture of radiant wavelengths of energy. Like a radiant body becomes hotter, few of the radiant energy is in the visible range of wavelengths such as the filament of a light bulb. Still hotter objects like the Sun emit energy across the whole range of wavelengths including very high energy radiation such as x and gamma rays. This is the just only way that heat is removed from the contents of a thermos or vacuum bottle. By eliminating all the air molecules from the space around the contents of the thermos, you remove loss of heat by conduction and convection.