RADIATION!


Another way of transfering thermal energy is radiation.
Radiation is the emission of infrared waves from the surface of all bodies,transmitted without the aid of a medium. These infra red waves travel through straight lines.
Radiation, unlike convection and conduction can take place through a vacuum. Eg. The sun emitting thermal energy to te Earth uses radiation. It emits its energy through electromagnetic waves . Heat readiation is able to travel all directions!

A good emitter of radiant heat is also a good absorber.
A poor emmiter of radiant heat is also a poor absorber.


Factors affecting infrared radiation:D
Colour and texture
-black surfaces are better absorbers and better emmiters of infrared radiation
-shiny and white surfaces are poorer absorbers.
-rough surfaces are better for heat transfer


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

Surface area
objects with a larger surface area will emit infrared radiation at a higher rate


Applications of radiation[:

Vacuum flask is designed to keep liquids hot through conduction,convection,evaporation and radiation. Conduction and convention through are prevented by the vacuum between the double-glass walls of the flask. Conduction through the trapped air is minimal since air is a poor conductor of heat. The stopper is made of plastic which is a poor conductor of heat. The walls of the glass are silvered so as to reflect radiant heat back into the hot liquid.

TAKEN FROM:http://www.blurtit.com/q965156.html

GREENHOUSE

CONVECTION!

Another process of thermal energy is convection.

convection is the transfer of thermal energy by means of currents in a fluid like liquids or gases.

Examples of convection in water:

convection in air: HOW DOES CONVECTION WORK?

Convection only occurs in fluids like liquids and gases but not in solids. This is because convection involves bulk movement of the fluids where the heat transported is by movement of heat particles. however for solids,thermal energy is transferred from one particle to another by vibration,without bulk movement.

Convection in water happens when water is heated,it expands. The expanded water will be less dense than its surroundings,and hence it will rise. The cooler parts of the water is now denser,and hence it starts to sink. Therefore,this will form a convection current.

Convection in air is similar. The hot air rises as it is less dense than the surrounding air. Hence,the cooler air being denser,will sink to take the place of the hot air. Hence,this will also form a convection current:D

For example, you can set up an experiment.

First,fill a beaker of water,then add a drop of coloured dye.

Put a bunsen burner under the beaker of water with the dye.

Slowly,you will be able to observe that the dye will slowly spread throughout the whole beaker of water.

This is because of convection. the water at the bottom of the beaker with the dye will get heated up first. Since it has lesser density now,it floats up,causing the cooler water to sink.

Hence,soon,the whole beaker of water will soon be filled with the dye:D

An example of convection is like the land and sea breeze.

In the day, the air on the land will tend to get hotter than the air in the sea. The hot air above the land will rise, and the cool air above the sea will sink to take the place of the hot air. Hence,that is known as a sea breeze.

At night, the air in the sea will tend to get hotter than the air on land. The hot air from the sea will rise,and the cool air on land will sink to take the place of the hot air. Hence,this is known as a land breeze.:D

Applications on convection[:

AIRCON

KETTLE

The heating coil of the kettle is always placed at the bottom because as the water in the kettle starts to boil, the water at the bottom of the kettle starts to heat up,resulting in te hot water to rise. The colder water sinks, so as the water around the heating element gets hot, it rises while it is heating, with the cold water taking its place.

FRIDGE

OVEN

HELLO:D
Transfer of Thermal Energy
Thermal energy always flows from a region of higher temperature to a region of lower temperature.
Thermal energy is the same as heat energy
thermal equilibrium is when there is no temperature difference between the two regions
Thermal energy can be transferred by conduction,radiation and convection.but today i will just post on conduction:P

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

-Conduction takes place in things like solids and liquids and gases.

-there are 2 types of conduction. one is free electron diffusion and the other is molecular vibration.

MOLECULAR VIBRATION->the way heat is mainly transported.

FREE ELCTRON DIFFUSION->it is the reason why metals are conductors while non metals are insulators[:

Different materials can conduct heat at different rates.there are good conductors like metal and poor conductors of heat like wood. Conduction takes place by when thermal energy is transferred,the particles nearer to the hot end will start to vibrate and will collide with the neighbouring particles,which causes them to vibrate too,which will increase the temperature.

the reason why metals are conductors and non metals are insulators is because of free electron diffusion. when metals heat,the free electrons move faster resulting in more kinetic energy. These fast-moving, energy carrying electrons diffuse or spread into the cooler end of the object by colliding with them hence heat is transferred.

taken from:http://www.rusticgirls.com/online-physics-help/free_electron_difussion.htm

An experiment that can be done is:

1)Put a small piece of butter on an aluminium foil

2)light up a candle
3)Place the stick about 3 inches above the flame and start timing it.
4)When the butter melts and falls off, stop the stopwatch and record the time.
-Repeat this for the other 3 metal sticks(copper,zinc and iron)

taken from:http://www.wikihow.com/Do-a-Simple-Heat-Conduction-Experiment

WHY DO METALS HEAT UP FASTER THAN NON METALS?

Metals contain more free electrons which are able to move randomly between molecules than non-metals where there is less collision.This explains why the rate of heat transfer is faster in metals than in non-metals[:

Conduction in liquids and gases is due to the collision of molecules over each other,and the conduction rate is slower than in solids:D However,molecules in liquids and gases are less prone to collision as they are not closely packed.

Applications of conduction[:

-Good conductors of heat:

Cooking utensils

These cooking utensils are often made of aluminium or stainless steel.

SOLDERING IRON RODS

These iron rod have a tip made out of copper as copper is a good coonductor.

Insulators:

Handles of utensils

The handles of utensils are often made of poor conductors of heat like plastic or wood. Hence,when we pick up these utensils,we will not get burnt:D

Table matThese tables mats are made of cork so that when hot plates of food is placed on it,the tabe will not get burnt.

Woollen clothes

Woollen clothes ar meant to keep people warm on cold days(:

HELLO:D