Transfer Of Thermal Energy PDF

- Thermal energy is always transferred from a religion of higher temperature o a region of lower temperature. - 3 Ways thermal energy can be transferred - Conduction - Convection - Radiation - Conduction - Conduction is the flow of thermal energy through matter from a religion of...

- Thermal energy is always transferred from a religion of higher temperature o a region of lower temperature. - 3 Ways thermal energy can be transferred - Conduction - Convection - Radiation - Conduction - Conduction is the flow of thermal energy through matter from a religion of higher temperature to a region of lower temperature without the movement of matter as a whole. - Conduction Can only take place in solids as solids are the best conductor of heat and gases and liquids are not. - In solids when a metal is heated up the particles start to vibrate more vigorously and transfer this excess energy onto the next particles. In metals there are also free electrons as well. When given energy moves faster to the other parts of solids and interacts with particles there to transfer thermal energy much faster. - Hence because of the free electrons metal is a better conductor of heat than liquids and gases (Insulator). - Convection - Convection is the method in which thermal energy travels through fluids (Liquids and Gases) - Convection occurs due to the difference of density. - When fluids are heated they expand and hence become lighter due to which it rises - Then that vacuum is filled by the colder liquid or gas from above. - This flow of liquid or as is called convection - As they are heated, they expand and their density decreases. - Radiation - Radiation is another way in which thermal energy is transferred. - However radiation does not require a medium, it can take place in a vacuum as well. - Thermal Radiation is just infrared radiation which is an electromagnetic wave. - All objects emit infrared radiation. - Dull and black objects are better absorbers and emitters of radiation, and are a poor reflector of radiation. - Shiny and white surfaces are poor absorbers and emitters of radiation but are a good reflector of radiation. - Uses of conduction in daily life - Utensils in the kitchens are made of metal to speed up the process of cooking - Utensils handlebars are made from insulators to prevent the handles to heat up - Winter clothes are made from wool which trap air and provide thermal insulation. - Double glazed windows are used as they trap heat and provide thermal insulation, as air is used for thermal insulation materials that trap heat become effective in thermal insulation - Radiators of cars are made of metal to absorb heat from the water cooling the cars engine - We use table mats used of cork to prevent conduction - Uses of Convection in real life - Convection is used by heaters installed in our homes, hot air rises and circulation throughout the room is possible, it is best to install heaters at a lower height relative to the room - Convection is also used by the hot water tanks and kettles - Uses of Radiation in real life - Infrared thermometers are widely used in airport and hospitals, they detect thermal radiation emitted by an object and convert it into a electrical signal, the temperature is determined by a radiant power and it is a non contact way of finding out the temperatures of objects - Application involving more than one energy transfer - In a car radiator both conduction and radiation take place, As the coolant moves throughout the engine and cools the engine by absorbing the heat given out by the engine, and then the coolant passes through the radiator which absorbs the heat of the coolant and radiates it out into the environment to cool it self. - In a wood or a coal fire both involve the transfer of heat energy through convection and radiation, during the fire heat is radiated out in all directions, while hot air with low density moves upwards and is replaced by the colder air with higher density forming a convection current. - A vacuum or a thermos is used to keep cold water cold and hot water hot, by preventing conduction,convection and radiation. it uses a double walled glass which has a vacuum which does not allow conduction or convection to keep place and has slivering both walls from the vacuum as silver is a bad absorber hence radiation is also prevented.