by the way, Mr Lim, I can't seem to upload pictures of any kind.

-Bindhu

Radiation

Radiation is defined as the 'continual emission of infrared waves from the surface of all bodies. transmitted without the aid of a medium'. This simply means that it does not require a medium for energy transfer. Radiation occurs everywhere- from the Sun's rays to vaccuum flasks.

However, there are certain factors that affect radiation- the amout of it and the it's rate.

Colour & Texture of a surface.
Dull black surfaces absorb heat faster and hence are better for radiation than shiny, bright surfaces are. This also means that they emit heat faster and hence are better emitters of infrared radiation.

Surface Temperature
Surface area is the amount of material exposed. If the material has more exposure and two objects that have the same mass, same colour but one has more surface area exposed it will be the one that absorbs/emits infrared radiation better.

Common Applications for Radiation

Greenhouses are used in cold climates to help vegetation grow. This works by it trapping heat. Inside the greenhouse, the grow warm and it emits infrared radiaton.

Teapots are also good applications of radiation. As tea is supposed to be drunk warm, the shiny, bright surfaces of the teapots keep the tea warm for longer as infrared radiation will not be emitted. This concept works two ways- as they are poor absorbers of infrared radiation cold tea stays cold and does not become room temperature.

Convection is defined as the 'movement of molecules within fluids'. This means that it does not occur within solids but only within liquids and gases. This is because convection is mainly the bulk movement and it carries the thermal energy with them. However, solids transfer heat through vibrations and no bulk movement of the atoms/molecules occur.

Convection works differently for both liquids and gases.

Convection In Liquids
for example, when a pot of water is put to boil, this is how convection occurs. When the water at the bottom of the flask is heated, it expands. This expanded water is less dense than the water that has not been heated. As a result, it rises. The unheated or cooler body of water sinks, as a result of being denser. The movement of water as a result of the density changes is called the convection current.

Convection in Gases

if air is heated, it also gets denser than the unheated air. As a result, it rises. The cooler air sinks and replaces the warmer, less dense air. It replaces the less dense air. This is the convection current occuring in gases.

Application of convection.

Electric kettles are prime examples of convection. They have something called an electric coil. These coils are always placed at the bottom of the kettle and renders itself helpful by transferring the heat to the water via convection.

This is how it works: power is switched on, and the electrical energy heats up the heating coil and the water is heated up. The less dense water rises and the cooler water sinks.

CONDUCTION

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


This simply means that conduction is the flow of heat energy through a medium/body. However, different materials have a different range of conductivity. Metals are usually the best conductors, while wood is usually the worst.






A simple experiment can illustrate this concept. First, you will need a wedge of butter, metal sticks(4 preferably: one of them zinc, another aluminium, iron and lastly, copper) and a candle.

Next. you place the wedge of butter on one of the metal sticks and heat it using the lighted candle. Record the time taken for the butter to melt and fall off. Repeat the experiment with the other metal sticks, and you can see the varying degrees of conductivity certain materials have.

Also, from this experiment, 2 other conclusions can be drawn:
firstly, conduction does not involve the material itself flowing. Merely the butter melted, and it did not alter the metal stick.
it reiterates that different materials have different levels of conductivity, even if they are all metals.

The process of conduction has to do with the atoms and molecules that make up the solids. Metals and non-metals differ greatly when it comes to whether they are insulators or conductors because metals contain many free electrons. These free electrons move randomly between atoms or molecules. Non -metals however, do not have them.

For instance, if a wooden rod and a copper rod were taken and heated at only one end, the atoms or molecules vibrate rigorously. They collide with other particles and they vibrate as well. Hence, kinetic energy is produced from the vibrations from the hot end. They are then transferred to the neighbouring atoms or molecules.

This happens in both the copper and wooden rods. However, as there are free electrons in the copper rod another process takes place. This is known as free electron diffusion.


When the copper rod is heated, the electrons in the copper rod gain kinetic energy through the vibrations. They then diffuse or spread into the cooler (or un-heated) parts of the metal. They collide with cooler parts in the metal and the kinetic energy is transferred to the cooler parts of the metal.

Conduction in Liquids & Gases
Liquids and gases are also matter. As this is so, they can also be transferred. That is- conducted from a hotter body to a colder body. However, conduction in liquids and gases is not as fast as conduction in solids. This is so as the atoms in solids are much closer together.

Application for Conduction

in the application of conduction, good and bad heat conductors are used. Cooking utensils- woks, kettles and saucepans are usually made up of metal to conduct heat and cook food faster.

Bad heat conductors are used for cooking utensil handles. This is to make sure that you do not get burnt when holding the utensils. As tabletops are usually glass, tablemats are made up of insulators to prevent damage. Also, woolen clothes can be used as examples of conduction. They are used to prevent coldness from reaching a body.

Thermal energy is transferred in three different ways, and they are: conduction, convection and radiation.

The only and only cause for the transfer of thermal energy is when it thermal energy flows from a body of high temperature to one of lower temperature.

A simple experiment can show the causes of thermal energy. In this experiment, fill up three basins with hot, warm and cold water respectively. Place your left hand in the basin filled with cold water and your right in the basin filled with hot water.

After half a minute of soaking your hands in it, place both your hands in the basin filled with warm (or room temperature) water and while your left hand will find it hot, your right hand will find it cold.

However, if right away you soak your hands in the basin filled with room temperature water, your hands will not feel cold nor hot as this is thermal equilibrium and there is no gain nor loss in heat.

Thermal Energy!

It is a form of energy that is produced when temperature is increased. Therefore, it is the kinetic energy of the movement of molecules and atoms.

Hence, when you boil water you are contributing to the presence of thermal energy.

As it is a form of energy, it can never be destroyed but be transferred.