8:46 PM
Friday, September 5, 2008
8:49 AM
EVAPORATION
drying of hair
movement of paricles during evaporation
puddle of water evaporating
CONDENSATION
condensation occuring on a cup
changing of state [gas => liquid]
BOILING
boiling point
boiling of water
MELTING
ice cube changing its state
melting point
SOLIDIFICATION
candle wax solidifying
a cup of water freezing
change in movement of particle during freezing
7:40 AM
CHAPTER 9- Temp is the degree of HOTNESS and COLDNESS of a body!!! Heat is the amount of thermal energy flowing from HOTTER region to COLDER region~ Internal energy is the total energy of the particles held by strong bonds - potential energy & kinetic energyKINETIC COMPONENT--> due to vibration of particles--> the higher the temp, the more vigorous vibration is--> in liquid / gas, particles move. thus, KE is due to movementPOTENTIAL COMPONENT--> due to stretching / compressing of bond as particles vibrate--> amt stored in bond depends on force between particles and how far they areMelting & Solidification+ solid => liquid: MELTING+ melting occurs at a certain temp, it is the MELTING POINT+ melting pnt: 0 degree celcius [ice => water]+ when bonds are broken, melting occurs+ hence, the molecules are able to move out of their fixed positions + liquid => solid: FREEZING / SOLIDIFICATIONBoiling / Condensation+ liquid => gas: BOILING+ the temp where it boils is called BOILING PNT+ boiling point: 100 degree celcius [water => steam]+ molecules move apart, boiling occurs+ gas => liquid: CONDENSATION+ thermal energy is given outEvaporation+ liquid => gas: EVAPORATION!!! evaporation occurs at ANY temperature+ thermal energy is carried away+ collision of air molecules rebounds some molecules+ occurs at SURFACE of water~ experience cooling effect on skin~ puddle of water dries up~ lowers tempFactorS AffectinG RatE Of EvaporatioN1. Temperature - rise of temp increases rate of evaporation 2. Humidity of surrounding air - increasing rate of evaporation decreases rate of evaporation - rate of evaporation increases with lower humidity 3. Surface area of liquid - larger surface area, rate of evaporation increases - more molecules escapes with larger exposed area4. Movement of air - moving of air remove molecules of liquid when they escape from the surface - rate of evaporation increases when surrounding air is moving5. Pressure - reduced in pressure increases rate of evaporation6. Boiling point of liquid - liquids with LOWER bp evaporates FASTER
6:53 AM
CHAPTER 8
Common Applications of Convection1. Electric Kettles
+ heating coil is placed at the bottom to help in transfer of energy in water by convection+ when power is switched on, water is heated+ it expands and become less dense
2. Household Hot Water Systems
3. Air Conditioners
+ the rotary releases cool dry air
+ cool air is denser hence it sinks
+ warm air being less dense is drawn to where is cooled
+ air is recirculated, temp falls
air conditioners
4. Refrigerators
+ freezing unit placed at the top to cool air and facilitate sets up convection currents
Common Applications of Radiation
1. Teapots
+ shiny surface are BAD emitters of radiation
+ shiny teapots keeps the tea warm and they are BAD absorbers of radiation
+ it can also keep cold liquid cool
shiny teapots
2. Greenhouse
+ help plants to grow better by trapping heat during cold weathers
+ during the day, infrared radiation warms the soil and plants
greenhouse
3. Vacuum Flasks
+ helps to keep liquid hot
+ minimises heat loss through CONDUCTION, CONVECTION, RADIATION, EVAPORATION
4:42 AM
Factors which affects RATE OF INFRARED RADIATION1. Colour / texture of surface
BLACK- better absorbers, emitters of infrared radiation2. Surface Temperature~ higher temp of surface relative to surrounding temp, the higher rate of infrared radiation3. Surface Area
~ object with larger surface area, emits infrared radiation at higher rate
USES OF GOOD CONDUCTORS OF HEAT
1. Cooking Utensils
+ direct heating is involved
frying pan
cooking pot
saucepan
kettle
2. Soldering Iron Rods
+ copper is a better conductor of heat than iron
3. Heat Exchangers
+ save energy
USES OF BAD CONDUCTORS OF HEAT
1. Handles of Appliances or Utensils
+ hot surfaces can b picked without scorching our hands
teapot
handle of saucepan
2. Table Mats
+ can be placed on without damaging tabletop
table mat made of cork
3. Sawdust
+ cover ice block to reduce melting
sawdust
4. Wooden Ladles
+ for scooping or stirring hot soup
wooden ladles
ladle
5. Woollen Clothes
+ to keep people warm duing cold days
woolleen clothes
6. Fibreglass, felt, Poylstyrene foam+ trap large amt of air
fibreglass
3:22 AM
ThErMaL EnErGy
+ transferred ONLY when there is a difference in temp
!!! flows from region of HIGHER temp TO region of LOWER temp
--> THERMAL EQUILIBRIUM:no gaining or losing of thermal energy
transferred through CONDUCTION, CONVECTION, RADIATION
ConductioN
!!! a process whereby thermal energy is transferred without flow of any material medium
the words are kind of BLUR
- different materials conduct heat at different rates
- METALS are good conductors of heat
- NON-METALS are poor conductors of heat [insulators]
IN SOLIDS
- tiny particles culd be found in ALL solids [atoms, molecules]
- metal contains many free electrons
- non-metals does not contain any of it
+ particles at hot end vibrates vigourously, colliding with other particles causing it to vibrate as well
+ when metals are heated, the free electrons in it gain KE and so it moves faster
+ those electrons as a result diffuse / spread to cooler parts
frying of egg involves conduction!! WOW! =)
IN LIQUIDS / GAS
~particles are further apart so there collisions of particles are LESS frequent
~ transfer of KE is slower
POOR conductor of heat
ConvectioN
!!! transfer of thermal energy by means of currents in ONLY fluid [liquid, gas]
- involves movement which carries thermal energy
-for SOLID, thermal energy is transferred from one particle to another through VIBRATION
+ when water is heated, it expands
+ it is less dense than surrounding water therefore it rises
+ cooler region is denser therefore it sinks
RadiatioN
!! continual emission of infrared waves from surface of ALL bodies, transmitted without medium
- can take place in vacuum
- thermal heat from infrared waves is called RADIANT HEAT
2:53 AM
Chapter 7 [Kinetic Model Of Matter]
BROWNIAN MOTION
- irregular motion of smoke particles in the air
- occurs only in fluid that has ability to flow / particles that are able to move freely [gas, liquid]
-->smoke particles at higher temp causes the motion of smoke particles to be more vigorous and air molecules move at greater speed
--> air molecules bombard smoke particles more vigorously
--> larger amt of thermal energy is converted to KE when temp increases, hence, molecules move faster
condensation occuring on a cup
boiling point
boiling of water
melting point
