Thursday, September 4, 2008
CHAPTER 8 - TRANSFER OF THERMAL ENERGY
NOTE!
- Thermal energy is transferred only when there is a difference in temperature
- Thermal energy always flows from a region of hgher temperture to a region of lower temperature
HOW IS THERMAL ENERGY TRANSFERRED?
Energy can be transferred in 3 ways: conduction, conection and radiation.
Conduction
Definition:
Conduction is ather process of thermal energy transfer without any flow of the material medium
Eg. when one end of a metal rod is heated,
the other end will soon be heated up as well.
this shows that energy is transferred.
HEAT IS TRAVELLED THROUGH A MEDIUM IN CONDUCTION!
Different materials conduct heat at different rates.
Metals such as copper, siver and iron are good conductors of heat.
Non-metals such as glass, plastic, water and even air are insulators (or poor conductors) of heat
and HOW DOES CONDUCTION WORK?
the difference between metals and non-metals is that metals have spare electrons and non-metals don't.
the SPARE/FREE electrons move freely and randomly between atoms.
When an atom in metals vibrate, the free electrons gains kinetic energy and causes the other atoms to vibrate as well, causing heat to be transferred at a greater speed as when compared to non-metals.
CONDUCTION in liquids and gases
The particles in gases and lquids are spaces further apart as when compared to that in solid, therefore there is lesser collision in liquids and lesser in gases.
The Transfer of kinetic energy from fast-moving particles to neighbourin particles are slower and that's why air is a better insulator as compared to water.
Convection
Definition:
Concection is the transfer of thermal energy by means of currents in a fluid (eg. liquids and gases)
HOW DOES CONVECTION WORK?
Convection can only work in FLUIDS! sch as liquids and gases.
(not in solids).
i actually found the same video a CHARA!
but here's something that we can use in our everyday life about how convectin currents affect global warming.
Radiation
Definition:
Radiation is the continual emission of infraread waves from the surfec of all bodies transmitted without the aid of a medium
OOH! same picture as chara again :D
-Radiation DOES NOT require a medium for energy tranfer!
- meanig, radiation can take place in a vacuum
- eg. thermal energy reach the Earth from the Sun through radiation.
- convection and conduction cannot be performed because there is no medium.
Thermal heat from Infrared waves(EM waves) are called radiant heat.
the hotte an object, the greater the amount of radiat heat.
The absorption of radiat heat causes the temperature in an object to increase.
Factors that affect the rate of infrared radiation
- Colour and textre of the surface
- Dull surfaces absorb radiation better than shiny white surfaces.
- Dull surfaces are also better emitters of infrared radiation
- Surface temperature
- The higher the temperature of the surface of the object
relative to the surrunding temperature, the higher the radiation.
- meaning: the higher the surface temperature as compared
to the surrounding temp.
- Surface area
when 2 objects with the same material andmass but different surfaces area, the one with the larger surface area will emit infrared radiation at a higher rate.
ALRIGHT! LAST PART!
Applications of thermal energy transfer!
for CONDUCTION:
- cooking utensils such as kettles, saucepans and boilers are made of aluminiu or stainless steel due to direct heating
- Soldering iron rods are made of iron with copper tips as copper is a better conductor of heat than iron
- SOLDERING: is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint.
- you can use soldering for electric guitar strings! that's what my friend does :D
INSULATORS!
- handles of kettles and saucepans
- table mats (to prevent damaging or table tops)
- sawdust (to cover ice blocks to prevent it from melting)
- Wooden ladles (for stirring or scooping hot food)
- Woollen clothes (for cold days)
for CONVECTION:
- electric kettles (heating coil causes convection currents)
- household water systems (designed based on convection in liquids)
- everyone's favourite AIR-CONDITIONERS
- refrigerators (cool air comes down and heat goes up!)
for RADIATION:
- Teapots (shiny surfaces keeps heat IN)
- Greenhouses (shiny glass traps heat in greenhouses and allows heat to go in)
- Vacuum Flask (deisgned to minimise heat loss)
THAT'S ALL FOLKS!
FOR CHAPTER 8!
HOLLA!
the journey goes on....
11:23 PM
11:23 PM