Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer...
-
Upload
solomon-johnson -
Category
Documents
-
view
221 -
download
0
Transcript of Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer...
![Page 1: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/1.jpg)
Transfer of Thermal Energy
Sec 3 Physics
![Page 2: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/2.jpg)
What we are going to learn
The 3 methods of heat transfer and
how they are applied in everyday application.
![Page 3: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/3.jpg)
3 Processes of Heat Transfer
Conduction
Convection
Radiation
![Page 4: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/4.jpg)
CONDUCTION
Occurs mainly in solids
Conduction takes place when there is
Molecular vibration
Free electron diffusion
![Page 5: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/5.jpg)
Molecular Vibration
When one end of a solid is heated, the molecules at the hot end gain energy and their kinetic energy increases.
They start to vibrate more vigorously and in the process, collide with their neighboring molecules. In doing so, some energy is transferred to the neighbours.
The neighbour molecules gains energy and starts to vibrate more vigorously. The cycle continues until the other end is also heated.
![Page 6: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/6.jpg)
Free electron Diffusion
Free Electron diffusion takes place only in metals as only metals have free moving electrons.
When heated, the free electrons gain energy and move quickly towards the cold end. In the process, they collide with molecules and transfer energy to them. This helps to increase the rate of heat transfer.
![Page 7: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/7.jpg)
Conduction
Question:Why is conduction not the main form of heat transfer in liquids and gases?
Answer: Liquid and gas molecules are spaced further apart so it is very slow to transfer energy by molecular vibration.
![Page 8: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/8.jpg)
Comparing the 2 mechanisms
Molecular vibration Free electron diffusion
Occurs in all solids
Slow process
Occurs in metals only
Fast process
Metals are better conductor because they have 2 mechanisms of conduction taking place at the same time whereas non-metals only have one.
![Page 9: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/9.jpg)
Conductors and Insulators
Materials that can conduct heat fast are known as conductors (e.g. metal).
Materials that are slow in conducting heat are known as insulators (e.g. water, trapped air, wood, plastic)
![Page 10: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/10.jpg)
Applications of good conductors
Good conductors are used when heat transfer needs to be fast.
Uses of good conductors: metal cooking utensils, copper pipes in car radiators and water heater and heat sinks*
*Heat sinks are components that conducts heat away from electronic equipment to prevent overheating.
![Page 11: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/11.jpg)
Applications of poor conductors
Materials that trap air are good insulators e.g. wool, styroform and double glazed window.
They are used when heat transfer needs to be slowed down.
Uses of good insulators: wooden handle of cooking utensils, containers to hold hot drinks (styrofoam cups), winter wear made of wool etc.
![Page 12: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/12.jpg)
Convection
Occurs in liquids and gasesDoes not occur in solids because the
molecules are not free to move around
![Page 13: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/13.jpg)
What happens during convection
Water at the bottom is heated and it expands.
When water expands density decreases.
Heated water starts to rise because of its lower density
Cooler water of higher density will be displaced to the bottom.
The cooler water gets heated and the cycle repeats.
Convection currents are set up to heat the water evenly.
![Page 14: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/14.jpg)
Applications of convection
Air con is usually placed at the top of a room.
Heating coil of a kettle is usually at the bottom
Formation of land and sea breezes
![Page 15: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/15.jpg)
Radiation
Radiation is the transfer of heat by electromagnetic wave (Infrared Radiation).
When an object absorbs radiation, it will convert it into thermal energy.
Radiation does not require a medium to transfer heat. (can occur in a vacuum)
![Page 16: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/16.jpg)
Emitters and Absorbers
An object will absorb heat when it is
![Page 17: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/17.jpg)
Good & Poor Emitters/Absorbers
A good emitter would also be a good absorber.A poor emitter would be a poor absorber.
Good emitter/absorber Poor emitter/absorber
Dull, black surfaceRough surface
Shiny, silver surfaceSmooth surface
![Page 18: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/18.jpg)
Factors affecting radiation
Colour and texture of the surface (refer to previous slide)
Surface temperature
Higher surface temperature, higher rate of transfer.
Surface area
Larger surface area, higher rate of transfer
![Page 19: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/19.jpg)
Applications of radiation
TeapotsThe greenhouseColour and texture of clothingsSkin cancer
![Page 20: Transfer of Thermal Energy Sec 3 Physics. What we are going to learn The 3 methods of heat transfer and how they are applied in everyday application.](https://reader030.fdocuments.us/reader030/viewer/2022033100/56649f455503460f94c6698f/html5/thumbnails/20.jpg)
The vacuum flask
The vacuum prevents conduction and convection
The silvered surfaces reduces radiation
Cap and base are made of good insulators to reduce conduction