hi, yes yes so this is my physics notes and first aid blog. which hopefully by the end f the holidays would cover most of the topics needed and all the importatnt notes and exercises needed for revision.
the notes are still being updated. the late updates are due to house under renovation and being ill for a long time so please excuse the lack of posts T_T they'll be all up veryvery very soon...
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intro to heat! + conduction notes
intro to heat-
heat is not a substance but an energy which can be gained or lost via the principle of conservation of energy. thus it cannot be made or destroyed but only transferred from one substance to another.
* note * students often mix up what is thermal energy and what is heat.Q. what is the difference of thermal energy and heat?Thermal energy is the energy portion of a system that increases with its temperature while heat is the TRANSFER of thermal energy.Q.What causes transfer if thermal energy ?It is the difference in temperatures between objects that allows thermal energy to flow from a region of higher temperature to a region of lower temperature (***the greater the difference of temperature the faster the heat transfer)Q. what is the difference between temperature and thermal energy?temperature is the measure of thermal energy whereas thermal energy is an energy.as the video stated, there are mainly 3 common methods of heat transfer.
1. conduction2. convection 3. radiationapplication notes~
** the greater the difference of temperature the faster the heat transfer
- when you put an iron to your hand (which i expect you to be more intellectual to decide wether you should or not) the heat travels much faster due to the graeter difference of temperature and you feel the heat very quickly
- a cold spoon put in a hot glass of water feels hot after awhile.
OK
so conduction
is the main mode of heat transfer in solids
1. heat is transferred form hot to cold
- in this diagram it shows that the vibration of a particle due to heat causes its neighbouring particles to vibrate more. the particles actually move futher from each other this is the actual reason why heated objects expand
Process
1. When a part is supplied with thermal energy, the molecules at this area gain kinetic energy. They vibrate faster and collide with the neighbouring particles
2. As molecules collide, there is kinetic energy transfer. The less energetic molecules gain kinetic energy, vibrate faster and collide with other less energetic molecules in the colder part of the object
3. Process continues until heat energy from the hotter part spreads throughout the colder area
Solids are better than liquids and gases because the molecules are much closer together. Since the atoms are closer together, solids conduct heat better than liquids or gasses. This means that two solid materials in contact would transfer heat from one to the other better than a solid in contact with a gas or a gas with a liquid
the expansion varies
- in which solids expand the most as their particles are close together thus increasing the capacity in which the particles move further form each other
liquids expand less as they are alraedy spaced apart alittle bit and of course gas expands the least as they are already far apart though heating will infact increase pressure due to more kinetic energy and the higher chance of particles hitting against the inner surface of a container.
os here is a common diagram proving how heat is tranferred from hot to cold ...
** metals are good conducters as they have free electrons unlike non metals which are poorer conductors
application ~
All metals are good conductors of heat. cooking pans, kettles, electric iron are made of copper, aluminium or steel. Plastic and wood are poor conductors but good insulators, therefore handles of cooking utensils are made of plastic or wood.
so what are good conductors and what are bad?
the good - metals
listing from
1. iron
2. steel
3.tungsten (application note- thats why these are used in light bulbs)
4. platinum
5.aluminium
6. gold
7.silver
8. copper
(notice the betetr ones are the ones with more number of free electrons)
the bad
1.vacuum (the worst ever...) ~ reason being - there are no particles in the first palce XD therefore there is no conduction as conduction requires particles to move and vibrate
2. air
3. water
4. non metals
posted by supermassive on Monday, June 22, 2009
