hoho. completed me physics post. sorry no tagboard.

Unit 9

Temperature and internal energy

Internal energy
- Particles in a solid vibrate about fixed position and are held together by strong intermolecular bonds. The total energy of these particles is called internal energy
- made up of two components – kinetic and potential energy

Kinetic component of internal energy
- due to vibration of particles
- The higher the temperature, the more vigorous the vibrations of particles
Potential component of internal energy
- due to the stretching and compressing of intermolecular bonds as the particles vibrate
- amount of potential energy stored in bonds depends on force between the particles and how far the particles are.

Melting and Solidification



Melting

Melting

- a process whereby when the solid state change to liquid state.
- The melting point of ice is 0, the constant temperature of which ice melts to become water.
- Although thermal energy is being absorbed during the change of state, the temperature remains the same.




Solidification




- solidification is basically a process changing from a liquid to solid state
- a pure substance will solidify or freeze at a temperature equal to its melting point.
- during the change of state from liquid to solid, there is no change in temperature even though thermal energy is lost to the surroundings.

Boiling


- Heating curve

When a state is heated and it changes to a vapor at a constant temperature, it is known as boiling.
(From the heating curve)The temperature remains steady at 100 degree celcius as the water boils and changes into gas/steam. This constant temperature at 100 degree celcius is the boiling point of water. During the change of state from water to vapor, there is no change in temperature even though thermal energy is being absorbed.

Condensation




Condensation is the change of state from vapor to liquid when a substance is cooled at the same constant temperature as in boiling. Thermal energy is given out during condensation.

Evaporation




Evaporation
- occurs at any temperature
- slow process
- takes place only at the liquid surface
- requires thermal energy from surroundings

applications of evaporation
- able to experience cooling effect on skin when perspiration evaporates
- wet clothes or puddles of water on pavements dry up after a while
- a person with high fever is sponge with water as when water evaporates, the temperature of patient can be kept down.
- Refrigerator uses principles of condensation and evaporation to keeps its content cold.

Factors affecting evaporation
- temperature > a higher temperature will increase the rate of evaporation
- humidity of surrounding air > Rate of evaporation decreases with increasing humidity
- surface area of liquid > rate of evaporation increases when there is more exposed surface area of the liquid
- movement of air > rate of evaporation also increases when the surrounding air is moving.
- Pressure > reducing atmospheric pressure increases the rate of evaporation
- Boiling point of liquid > liquids with lower boiling points will evaporate faster

End OF UNIT 9. BYES

Chapter 8 – transfer of thermal energy

Firstly, thermal energy always flow from a region of higher temperature to a region of lower temperature.
Secondly, thermal energy is only transferred when there is a difference in temperature.
Lastly, It is transferred by three processes, conduction, convection and radiation.

Starting from conduction

Conduction is The transfer of thermal energy through a medium, without medium moving.

(looks yummy) heeee

(We take it as the spoon is made of silver)
when u place the spoon into the bowl of boiling hot soup, u realized that the spoon eventually becomes warmer. This is due to the process of conduction. The cold end of the spoon becomes warmer as thermal energy is transferred from the boiling soup (hot end of the spoon) towards the colder end of the spoon.


But How Does It Work?

(linking back to the diagram again)
When the spoon in the soup is heated, the free electrons in the spoon gain kinetic energy and move faster. These fast-moving electrons then spread into the cooler parts of the spoon and then transfer the kinetic energy to them. As a result, good conductors of heat are more capable of transferring thermal energy at greater speed.

Conduction in liquids and gases.
The process of conduction in liquids and gases is inefficient.
Linking back to the previous post, I have shown that particles in liquids and gases are spaced further apart than those in solids, hence, collisions between particles are less frequent in liquid and even lesser in gases. As a result, the transfer of kinetic energy is slower.

Application of conduction

Uses of good conductor of heat.
- cooking utensils > kettles, saucepans and boilers
- soldering iron rods
- heat exchangers

Uses of insulators
- handles of appliances and utensils > kettles saucepans etc.
- table mats
- sawdust
- wooden ladles
- woolen clothes
- fiberglass, felt and expanded polystyrene foam


Convection



Convection is the transfer of thermal energy by means of currents in a fluid.
It occurs only in fluids such as liquids and gases but not in solids as convection involves the bulk movement of the fluids which carry thermal energy with them.

Convection in liquid



In this case, the water at the bottom expands and gain more energy when it gets heated up. As the heated portion of the water is less dense than the surrounding water, it rises. Meanwhile, the cooler regions of the water in the upper part of the flask, being denser, sink.
(use the purple “arrows” to represent the movement of the water)

common applications of convection
- electric kettles
- household hot water systems
- refrigerators
- air conditioners.

Radiation

Radiation is the continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium
- able to take place in a vacuum

Factors affecting rate of infrared radiation.

color and texture of surface
- dull, black surfaces are better absorbers and emitters of infrared radiation than shiny, white surface.

Surface temperature
- the higher the temperature of surface of object relative to the surrounding temperature, the higher the rate of infrared radiation.

Surface area
- the object with larger surface area will emit infrared radiation at a higher rate

applications
- teapots
- the greenhouse
- vacuum flasks

Hence. In conclusion for Unit 8






End of Unit 8.

hello :)) going to start from unit 7. sorry for the lack of pictures. :((

Different states of matter

- solid
- liquid
- gas


okay. I shall first start with solid.

Properties of solid
- fixed shape and volume
- normally hard and rigid
- large force is needed to change its shape
- high density
- incompressible

No. that’s not all. There is a reason for everything

The solid has high density due to the arrangement of particles.
As u can see from the above figure, it shows that the particle are neatly packed together, in a regular pattern, occupying minimum space.

Also, the solid has fixed shape and volume due to its movement of particles
The particles vibrate about fixed position only as they are held in position by very strong molecular bonds.

Coming up next. Liquid.

Properties of liquid
- fixed volume but not fixed shape
- relatively high density
- incompressible

arrangement of particles
Particles are arranged randomly with the particles slightly further apart which results in liquids having relatively high densities

Movement of particles
The particles moved freely but confined within the vessel. Also, the particles have attraction forces between particles. As a result, liquids have fixed volumes but the shape depends on the vessels containing them.

Lastly. Gas

Properties of gas
- no fixed volume or shape
- low density
- compressible

arrangement of particles
particles are far apart and randomly arranged and will occupy any available space. Which result in gases having low densities.

movement of particles
the particles have very little attraction between them and move about randomly at high speeds. As a result, gases have no fixed shape or volume and they are compressible.

Brownian motion.

- random or irregular motion of smoke particles in air
- Brownian motion only occurs in substance that has the ability to flow or has particles that can move freely (example: gas, liquid)

At higher temperature, a large amount of thermal energy is converted to kinetic energy of the air molecules, hence, the motion of smoke particles will become more vigorous and agitated as the air molecules are bombarding the smoke particles more vigorously and frequently. Therefore, higher temperature cause the air molecules to move in greater speeds.