THERMAL PHYSICS

2008-09-04T19:03:00.000-07:00

CHAPTER 9:

THERMAL PROPERTIES OF MATTER

Temperature and Internal Energy
SI unit for energy is joule(J)

Internal energy is made up of two components, namely kinetic energy and potential energy.

Kinetic component of internal energy is due to the vibration of particles.
the higher the temperature, the more vigorous it vibrates.

Potential component of internal energy is due to the stretchign and compressing of the intermolecular bonds as the particles vibrate.
the amount of PE stored in the bonds depends on the force and the distance between the particles

Melting and Solidification
Melting is a process where solids changes to a liquid state when heated.
[e.g. ice melts and change state to become water]
Melting point is known as the particular temperature for a PURE substance to melt.
Solidification is a process where liquids changes state when frozen.
[e.g.water freezes and change state to become ice]

Boiling and Condensation
Boiling is a change of state from a pure liquid to vapour when heated at a fixed or constant temperature.
Condensation is the change of state from vapour to liquid when cooled at the same constant temperature as in boiling.
In the process, thermal energy is given out.

Evaporation
Evaporation is the change of state from liquid to gas.
Evaporation can occur at any temperature.
The process of evaporation is much slower than boiling.
It also causes cooling.
Evaporation is an endothermic process because molecules must be supplied with energy to overcome the intermolecular forces.

Appications of evaporation
-cooling effect when apply perfume/ when perspiration evaporates
-Wet clothes do not take very long to dry
-Sponging a patient with high fever will keep the person's temperature down as water evaporates
-Refrigerator uses condensation and evaporation to keep the food cold

Factors affecting the rate of evaporation
-Temperature
-Humidity of the surrounding air
-Surface area of the liquid
-Movement of air
-Pressure
-Boiling point of the liquid

2008-09-03T19:46:00.000-07:00

CHAPTER 8:

TRANSFER OF THERMAL ENERGY

THERMAL ENERGY ALWAYS FLOWS FROM A REGION OF HIGHER TEMPERATURE TO A REGION OF A LOWER TEMPERATURE.

THERMAL ENERGY IS TRANSFERRED BY THREE PROCESSES, NAMELY:

- conduction

- convection

- radiation

CONDUCTION

Conduction is the transfer of energy through a medium

without the medium moving

This diagram shows how heat travels from a high temperature

to a low temperature during conduction

the process of conduction in liquid and gases is inefficient.

the particles in them are further apart, compared to those in solids.

thus, they wont bump into each other that often.

in coonclusion, air is a poor conductor of heat compared to water,

and water is a poor conductor of heat compared to most solids.

Applications of good conductors of heat
-cooking utensils
-soldering iron rods
-heat exchangers
Application of bad conductors of heat
-handle of appliances and utensils
-Table mats
-Sawdust
-Wooden ladles
-Woollen clothes
-Fibre glass, felt and expanded polystryene foam

CONVECTION

Convection is the transfer of thermal energy by means of currents in liquids or gases

Convection currents only occur in liquid and gases but not solids.
Its is because convcection involves the bulk

movements of the fluid which carry thermal energy with them.

Common applications of convection

- electric kettles

-household hot water systems

-Air conditioners

-Refrigerators

Radiation

Radiation is the continual emission of infrared waves from the surface of all bodies,transmitted without the aid of medium.

radiation can take place in vacuum

infrared radiation is absorbed by all objects and surfaces.

The absorption of radiant heat causes the temperature to rise.

Dull,black surfaces absorb infrared radiation faster compared to shiny,white surfaces

Dull,black surfaces are better emitters of infrared radiation than shiny,white surfaces

A GOOD EMITTER OF RADIANT HEAT IS ALSO A

GOOD ABSORBER OF RADIANT HEAT

Factors affecting the rate of infrared radiation

-Colour and texture of the surface

black surfaces are better emitters of infrared radiation than shiny or white surfaces

-Surface temperature

the higher the temperature of the surface of the object, the higher the rate of infrared radiation

- Surface area

an object with a larger surface area will emit infrared radiation at a higher rate

Common applications of radiation

-teapots

-the greenhouse

-vacuum flasks

2008-09-02T00:48:00.000-07:00

CHAPTER 7:

KINETIC MODEL OF MATTER

there are 3 states of matter. SOLID, LIQUID, GAS.

Solid
- Fixed shape
- Fixed Volume
- High Density
- Not compressible

Solids are closely packed together.
They are in a regular pattern, taking up only a little space
thus, they have high density

Solids vibrate about their own fixed positions ONLY.
Therefore they have fixed volume and shape:)

Liquid
- Fixed volume
- No fixed shape
- High density
- Not compressible

Liquids are arranged randomly,
therefore resulting in relatively high density

They are free to move about but are confined within the limited space
They have attractive forces between each particle
Therefore they do not have fixed shape BUT have fixed volume

Gas
- No fixed shape
- No fixed volume
- Low Denisty
- Compressible

They are arrange in such a way that they are very far apart from each other.
They are randomly arranged and will take up any space there is.
Therefore, they have a low density.

The particles have little attraction between them. They move about RANDOMLY at high speed.
Thus, they have no fixed shape or volume, and they are highly compressible.

Brownian Motion
- occurs only in fluids
- it is a random or irregular motion of smoke particles in air

2008-08-28T04:13:00.000-07:00

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