Thermal Physics

DONE

2008-09-02T18:16:00.004+08:00

Well, i completed my physics posts! :D

YAY! (:

anyways, not sure why got so many ppl viewed my blog, at one go.. 11 online cybers.-.-
i got a screenshot to prove it too. hahas!

ok, be original! dont come coping from my blog.
lols.

Yup, started on the 31Aug and ended today, 2sept.
hee.

Chapter 9

2008-09-02T04:07:00.012+08:00

Thermal Properties Of Matter.

Internal energy
- Particles in a matter(solid, liquid or gas) posses energy called internal energy.
- Comprises of 2 components:
1. Kinetic energy
2. Potential energy

The kinetic component
- Higher the temperature, the more vigorously the particles move.
• Kinetic energy is due to their movement instead of vibrations.

The potential component
- Due to the stretching and compressing of the intermolecular bonds as the particles vibrate.
- Amount of potential energy stored in the bonds depends on the force between the particles and how far apart the particles are.

• An increase in temperature leads to an increase in the kinetic component of the internal energy.

Melting

Heating Curve.

• When a solid changes to a liquid upon heating.
• Pure substances –melting occurs at a definite or constant temperature.

- The temperature goes up the longer the heating continues. However, there are two horizontal flat parts to the graph. These happen when there is a change of state.

• The first change of state is melting (changing from a solid to a liquid). The temperature stays the same while a substance melts.

• The second change of state is boiling (changing from a liquid to a gas). The temperature stays the same while a substance boils.

During melting
- Heat is absorbed to break the attractive force between the particles
- Allows them to break free from their fixed positions and are able to move about.

During boiling
- Heat is absorbed to break the attractive force between the particles
- Allows them to move freely and randomly in all directions.

Solidification.

- Reverse process of melting
- A pure substance will sodify or freeze at a temperature equal to its melting point.

Cooling Curve.

During condensation
-The motion of particles becomes less vigorous in order to form the attractive force between the particles when a gas changes into a liquid.

During freezing (solidification)
-Strong attractive force can be formed between the particles in order to be arranged in a regular pattern at their fixed positions.

Condensation

• A process whereby vapour changes into liquid at the same constant temperature. Heat is given out during condensation.
• During condesation, the temperature remains constant at the condensation point. Thermal energy is released by the substance.

Boiling and Evaporation

• Boiling is a process in which a liquid changes into a gas at the boiling point of the liquid.
• Evaporation is a process in which a liquid changes into a gas temperatures below the boiling point of the liquid.

Difference between boiling and evaporation.

Boiling
- Occurs at constant temperature
- Happens within the liquid
- Bubbles produced
- Rate of process: Fast

Evaporation
- Occurs at any temperature
- Only the surface of the liquid involved
- No bubbles
- Rate of process: Slow

Evaporation

• A cooling process
• Evaporation of a liquid is due to the molecules at the surface with energy greater than the average kinetic energy escaping from the rest of the liquid.

Factors affecting the rate of evaporation.

1. Temperature
- Higher the temperature of the liquid, the higher the rate of evaporation.

2. Humidity of the surrounding air
- Lower the humidity of the surrounding air, the higher the rate of evaporation.

3. Surface area of the liquid
- Greater the surface area of the liquid, the higher the rate of evaporation.

4. Movement of air

5. Pressure
- Lower the pressure in the surroundings, the higher the rate of evaporation.

6. Boiling point of a liquid

>Eureka! Episode 18 - Evaporation and Condensation, Video-YouTube

Chapter 8

2008-09-01T01:21:00.077+08:00

Transfer Of Thermal Energy.

•Thermal energy always flows from a region of higher temperature to a region of lower temperature.
•The greater the difference in temperature, the greater the heat flow.

•3 different processes of thermal energy transfer:
1. Conduction
2. Convection
3. Radiation

Difference between thermal energy and temperature.

Temperature
-Temperature is not a form of energy, it is only a measurement.
-SI Unit: Kelvin (K)

Thermal Energy
-A flow of energy from a hot object to a cold object
-Unit: joule (J)

>Eureka! Episode 21 - Temperature vs. Heat, Video-YouTube

1. Conduction

•Conduction is the process of thermal energy transfer without any flow of the material medium.

•Conduction is a point-to-point (by contact) transfer of energy. Molecules that are energetic impart energy to those nearby that are less energetic, thus increasing their temperature.

Heat transferred by conduction in 2 ways:
I. Through the vibrations of particles (atoms and molecules)
II. Through the motion of free electrons

I. Vibrations of particles

- Particles in solids vibrate at their fixed positions.
- Strong attractive force between them.
- When heat is supplied to one region of particles, they vibrate stronger and cause their neighbouring particles to vibrate stronger as well.

II. Motion of free electrons

Metals
- Good conductors of heat
- Have free electrons.
- Carry heat with them when they move from the hotter region to the colder region.
- The heat transfer is speeded up in this way.

Non-metals
Eg. wood, plastics or glass
- Are insulators
- Do not have such free electrons
- Particles are further apart
- Collision between particles are less frequent

>Eureka! Episode 24 - Conduction, Video-YouTube

2. Convection

•Convection is the transfer of thermal energy by means of currents in a fluid
(liquids or gases).

• Convection requires the movement of particles, so this process can only take place in liquids and gases.

Convection Current

- Is created due to change in density in different parts of the fluid.

>Eureka! Episode 27 - Convection, Video-YouTube

3. Radiation

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

- Does not require a medium for energy transfer.
- Take place in a vacuum.
- Heat from the sun reaches us by infrared radiation.

- Absorption of Infrared Radiation
•causes a temperature rise

- Emission of Infrared Radiation
•causes the temperature of the objects themselves to fall

-The rate of heat transfer by radiation is affected by the following factors:
I. Colour and texture of the surface
II. Surface temperature
III. Surface area

Factors Affecting rate of infrared Radiation

I. Colour and texture of the surface
-All objects absorb and radiate heat in different rate.
-Dull and black surfaces are better absorbers and radiator of heat. They are poor reflector of heat.

II. Surface temperature
- Hgher the temperature of the surface of an object compared to the surrounding temperature, the higher the rate of infrared radiation from the object to the surroundings.

III. Surface area
- Larger the surface area of an object, higher the rate of infrared radiation from the object to the surroundings.

>Eureka! Episode 29 - Radiation Waves, Video-YouTube

Applications of Thermal Energy Transfer

Applications of conduction

Common applications of conduction.
Good conductors of heat:

- Cooking Utensils
Eg. Kettles, Boilers

- Soldering Iron Rods
• tip is made of copper

- Heat Exchangers
• used in large laundry facility, help to save energy

Uses of bad conductors of heat (insulators):
• Minimise loss of thermal energy
• Prevent thermal energy from being transferred quickly

Bad conductors of heat:

- Handles of Applications and Utensils
• utensils can be picked up without scorching our hands

- Table Mats
• usually made of cork

- Wooden Ladles
• useful for stirring or scooping hot soup or rice that has just been cooked

- Woolen clothes
• keep people warm

Applications of convection

- In boiling water.

- A radiator in a room heats up the room by convection.

- Hot water system uses the concept of convection.

• With a convection circulation system set up, the hot water storage tank gradually becomes filled with hot water from the top downwards.
• When hot water is run off, an equal volume from the cold supply tank enters the hot storage tank at the bottom. The whole system is thus kept constantly full of water and no air can enter.

- Coastal breeze is an example of natural convection.

Applications of radiation

- Green house effect
• A warm environment.
• Short infrared radiation from sun passes through the glass panels of a green house, and is absorbed by the plants and soil inside.
• This radiation is reflected by the glass panels
• Temperature inside the green house increases until it reaches a thermal equilibrium suitable for plant growth.

- Vacuum flask
• Is a container that is used to keep liquids warm for a longer period of time.
• Its design has important features to reduce heat transfer from inside the flask to the surroundings through conduction, convection and radiation.

Plastic cap
• Made of material which is an insulator
- prevents heat loss by convection because hot air cannot escape

Trapped air
• air is a very poor conductor of heat
- reduces heat lose by conduction

Vacuum
• no particles in vacuum
- reduces heat loss by conduction and convection as both processes need particles to transfer heat.

Thin silvered glass walls
• silvered surface is a good reflector of heat
- it reflects heat back inside the flask, reduces heat loss by radiation

This picture somewhat sums up on chapter 8,

>Easy to Understand; web on
Conduction, Convection and Radiation.

Chapter 7

2008-08-31T23:06:00.015+08:00

Kinetic Model Of Matter.

• Matter is made up of particles.
• At room temperature, matter exists either as a solid, a liquid or a gas.
• The particles in a matter arrange and behave differently in a different physical states.

Properties of solids, liquids and gases.

Solid
• Fixed shape
• Fixed volume
• High density
• Incompressible

Liquid
• Does not have a fixed shape
• Fixed volume
• High density
• Incompressible

Gas
• No fixed shape
• No fixed volume
• Low density
• Compressible

>States On Matter, Video- YouTube

Kinetic model of particles in matter.

Molecular Structure:

Solid
- Motion: Molecules and atoms vibrate at fixed positions only
- Attractive Force: Very strong intermolecular bonds
• Show that solids have fixed volume and shape.

- Arrangement: Regular and fixed
- Distance: Very close together, occupying minimum space
• Results in solids having high densities.

Liquid
- Motion: Molecules and atoms move about within confined space
- Attractive Force: Moderate, found between particles

- Arrangement: Irregular and random
- Distance: Quite close
• Results in liquids having relatively high densities .

Gas
- Motion: Molecules and atoms move freely in all directions at high speed
- Attractive Force: Very weak, have very little attraction between particles
• Show that gases are highly compressible and that they have no fixed volume and shape.

- Arrangement: Irregular and random
- Distance: Very far apart
• Results in gases having very low densities.

>Eureka! Episode 16 - Molecules in Solids, Video-YouTube

>Eureka! Episode 17 - Molecules in Liquid, Video-YouTube

Use of kinetic model of particles.

Solids have higher melting points and boiling points that liquids and gases.
• The attractive force between the solid particles is very strong, so it requires more energy to break down the force between them.

Why can gases be compressed but not solids and liquids?
• Solids and liquids cannot be compressed because the particles are closely packed and there is very little empty space between them. Particles of a gas are far apart and there are lots of empty spaces between them, so they can be compressed.

Why does liquid have a definite volume but not a fixed shape?
• Particles in a liquid are held by strong attractive forces and are closely packed, so it has a fixed volume. The particles are not orderly, so the liquid can take the shape of the container.

Brownian motion

-Random or irregular motion of smoke particle
-Occurs only in fluids (liquid and gas)

Effects of temperature on molecular motion.
- The Higher the temperature, the more vigorous and agitated the smoke particles move.
- The Lower the temperature, the motion of particles will be less agitated.

• This is because as temperature increase, a larger amount of thermal energy is converted to kinetic energy of the air molecules, causing the molecules to move faster.

Thermal Physics

2008-08-27T20:23:00.002+08:00

Hmm,

my Thermal Physics blog officially opened today.
lols.

well, will get it done soon...(:

in the process of doing it...