1. Thermal energy always flow from a region of higher temp. to a region of lower temp. Net flow of temp. only occurs when ther is a difference in temp.
1.1. Conduction
1.1.1. Transfer of thermal energy through a mediam without any flow of the medium.
1.1.1.1. Metals
1.1.1.1.1. Free electrons: diffuse
1.1.1.1.2. Tiny particles: Vibrate
1.1.1.2. Non-Metals
1.1.1.2.1. Tiny particles: Vibrate
1.2. Radiation
1.2.1. Transfer of thermal energy in the form of electromagnetic waves such as infrared radiation without the aid of a medium.
1.2.1.1. All objects and surfaces emit infrared radiation. This causes fall in temp.
1.2.1.1.1. Vacuum Flask
1.2.1.2. All objects and surfaces obsorb Infrared Radiation. This causes rise in temp.
1.2.1.2.1. Green Houses
1.3. Convection
1.3.1. Transfer of thermal energy by means of convection currents in a fluid due to difference in density.
1.3.1.1. They only occur in liquid and gases. They do not occur in solid.Convection requires bulk movement of a fluid which carries the thermal energy.
1.3.1.1.1. Electric Kettles
1.3.1.1.2. Household hot water system
1.3.1.1.3. Air-Conditoners
1.4. Factors affecting emisson and absorption
1.4.1. Colour and Texture of surface
1.4.1.1. Dull and dark surfaces are better emitters and absorbers than shiny and silver surfaces
1.4.2. Surface Temp.
1.4.2.1. Higher the temp. in relation to the surrounding and higher the rate of emission
1.4.3. Surface Area
1.4.3.1. Larger surface emits and absorbs better.
1.5. Applications
1.5.1. Good Conductors
1.5.1.1. Cooking Utensils
1.5.1.2. Soldering Iron Rods
1.5.1.3. Heat Exchangers
1.5.2. Poor Conductors
1.5.2.1. Handles of appliances and utensils
1.5.2.2. Table Mats
1.5.2.3. Clothing of cold weather
1.5.2.4. Doubled-glazed windows