THERMAL PROPERTIES OF MATTER//Friday, July 3, 2009//8:02 AM
THERMAL PROPERTIES OF MATTER -heat: amount of thermal energy that flows from a hotter region to a cooler region -SI Unit(thermal energy): Joules(J) INTERNAL ENERGY -total energy of particles in solid which vibrate about fixed positions that are held by interatomic or intermolecular bonds -two kinds:kinetic energy : potential energy -kinetic energy (solids) :due to vibration of particles :directly related to temperature :higher the temperature, more vigorous the paricles vibrate -kinetic energy (liquids/gases) :particles are free to move:due to movement instead of vibrations -potential energy :due to stretching and compressing of interatomic or intermolecularbonds as the particles vibrate :amount stored in the bonds depends on the force between particles and the distance between them *If temperature of a substance rises, it is due to an increase in the average kinetic energy of it's particles only.
HEAT CAPACITY -amount of thermal energy required to raise the temperature of a body by 1J/K -factors that affect heat capacity: mass of object : material of the object
SPECIFIC HEAT CAPACITY -amount of thermal energy required to raise the temperature of 1 kg of a substance by 1K -more convenient to examine the SHC of the substance -same amount of thermal energy supplied, materials with lower SHC will heat up faster than materials with high SHC
*down in my heart;
;that's where memories hold on to.
CONDUCTION&CONVECTION////2:18 AM
there has been a problem with the uploading of videos so i have just included the url below.
CONDUCTION: http://www.youtube.com/watch?v=0cydb3TNEqk the above video is about an experiment that is similar to the experiment mr lim did in class. instead of using paper cups, this experiment uses balloons. when the flame is put under the balloon that was blown up, it popped as the heat capacity was lower the balloon. however, when the flame was put under the balloon that was filled with water, it did not pop as the heat capacity was higher than the balloon and the surrounding air.
CONVECTION CURRENT: http://www.youtube.com/watch?v=SjI4mhqKz5Y the above experiment used oil as the liquid in which the current is in. the oil is heated over a flame. the bottom region which was heated starts to warm and becomes less dense. it then starts to rise. the upper region however, is cooler and denser. therefore it would sink to the bottom where it would be heated. this process repeats itself over and over again, resulting in a convection current.
*down in my heart;
;that's where memories hold on to.
APPLICATIONS OF THERMAL ENERGY TRANSFER//Thursday, July 2, 2009//12:39 AM
CONDUCTIONcommon applications =>use of good conductors of heat : cooking utensils--------------> : soldering iron rods-----------> ALL MADE OF METAL : heat exchangers-------------> =>use of insulators - minimise loss of thermal energy : handles of appliances and utensils - prevent scalding : table mats - to prevent damaging the table top : sawdust : woollen clothes - to keep people warm : fibreglass, felt and expanded polystyrene foam - trap large amounts of air to use as insulators
CONVECTIONcommon applications : electric kettles : household hot water systems : air-conditioners : refridgerators
RADIATIONcommon applications : teapots : greenhouses : vacuum flasks (uses four ways of minimising heat loss: conduction, convection, radiation, evaporation)
*down in my heart;
;that's where memories hold on to.
CONDUCTION, CONVECTION, RADIATION//Wednesday, July 1, 2009//7:59 AM
CONDUCTION - "process of thermal energy transfer without any flow of the material medium" -metals: good conductors of heat non-metals: insulators/poor conductors of heat -mechanisms for conduction: atomic/molecular vibrations (for metals & non-metals) : free electron diffusion (for metals only)
CONVECTION - "transfer of thermal energy by means of currents in a fluid (liquids/gases)" -only applies to liquids & gases as it involves bulk movement of the fluids that carry thermal energy -do not apply to solids as thermal energy is transferred through vibrations CONVECTION CURRENT : movement due to the difference in the density of the liquid : "hot air rises, cold air sinks" theorem : when fluid is heated at the bottom of a flask, it expands, causing it to be less dense than the surrounding fluid and starts to rise :the cooler regions at the upper section being denser, sink :therfore causing convection current
RADIATION - "continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium" -can take place in a vacuum (eg. thermal energy from sun to the earth by radiation) RADIANT HEAT : thermal energy from infrared waves : all objects emit radiant heat : the hotter the object the more amount of radiant heat emitted because the absorption causes the temperature to rise : emission of the radiant heat causes the temperature of the objects to fall *GOOD ABSORBER=GOOD EMITTER POOR ABSORBER=POOR EMITTER INFRARED RADIATION : absorbed by all objects and surfaces : emitted by all objects and surfaces -FACTORS INFLUENCING INFRARED RADIATION :colour and texture of surface =>dull, dark surfaces are better absorbers and emitters compared to shiny, white surfaces :surface temperature =>the higher the temperature of the surface of the object relative to the surrounding temperature, higher the rate of infrared radiation :surface area =>the larger the surface area, the higher the rate of emission and absorption
*down in my heart;
;that's where memories hold on to.
////7:10 AM
THERMAL ENERGY - transferred only when there is a difference in temperature - always flows from a region of higher temperature to a region of lower temperature(just like diffusion and osmosis in biology) -thermal equilibrium : both bodies are of the same temperature and there is no net flow of thermal energy between them -transferred in 3 main processes : conduction : convection : radiation *Thermal energy can be conducted in ALL three states of matter! However, it is inefficient in liquids and gases.
MOST EFFICIENT LEAST EFFICIENT SOLIDS------------------------------------->LIQUIDS----------------------------------->GASES WHHHYYYYY???? -the particles in these two states are spaced further apart -collisions between particles are less frequent in liquids(worse in gases)
