radiation

RADIATION

DEFINATION: Radiation is the continual emission of in farared waves from the surface of all bodies, transmitted without the aid of a medium.

Radiation waves are effect of movement of energy , through waves .

Energy is transferred through the space between the an object and a source of energy.

Sun sends out heat energy through waves in every direction,called radius (radiation)
so , it is through radiation that sun transfer its heat energy to us , which make our molecules move faster, making us hotter.

Even though the sun is million miles away,by means of waves, heat energy is transferred to us .

-waves of heat energy are radiated by all sources of heat




one of the chief ways which heat energy moves is in the form of waves .sources of heat such as the sun or a fire or a stove ,send out these waves in all direction ,as if each wave were the radius of a wheel. this is why this third kind of heat transfer is called radiaton.

radiation spectrum
:colours come from white light .

When light shines on an object , it absorbs each of the colours except its own colour which they reflect.

white light is a combination of all the colours .white appears white because it does not absorb any of the colours and reflects them all.
black appears black because it absorbs all of the colours.
when sun radiates waves of heat energy,these waves come in many different forms, forming a spectrum of energy waves.

Light waves are the only waves visible,and they only take up a little of the radiation spectrum,the rest of the spectrum is not visible for an example (infrared radiation)

infrared radiation is emitted by all objects,causing its own temperature to drop.

most of the suns radiated heat energy comes in the visible and the infrared parts of the spectrum, black will feel warmer, because it not only absorbs the heat of the visible colours, but also the heat energy of the invisible infrared radiation .

conversely,white is cooler,as it not only reflects the heat energy of the visible colours and it also tends to reflect the a lot of the heat energy from he invisible infrared radiation.

thus a black objects would tend to feel warmer than white objects .

CONVECTION

DEFINATION: Convection is the transfer of thermal energy by means of currents in a fluid

the arrows stated are the convection currents.

Hot air rises, cool air sinks

in this picture, the sun heats the air on the ground of the atmosphere, the hot air(red arrow) rises as air travels from a region of low pressure(hotter)to a region of high pressure(cooler).then the upper part of the atmosphere becomes cool and sinks. this is known as convection.





The furnance is kept in the basement because water is heated and rises up to radiators and water cools and flows down to the furnance where it is heated up down .

Hot water goes up and hot water comes down due to The Principle of Buoyancy.
when water is heated , molecules expand and becomes less dense and thus rise . The water which rises is then cooled down and become dense again and goes down.

The principle of buoyancy applies to liquids and gas.
when air is heated,molecules expand and becomes less dense and rises, the air which rises cools down and becomes dense again and goes down.

Hot air balloons : when the air inside the balloons is heated and expands ,and there is not enough room for the expanded air molecules , some of the hot airs escapes and there is left with fewer air molecules inside the balloon than before .the air inside is less dense than the air in the surrounding , so the balloon goes upwards.

hot air rises and thus you are able to cook above the fire instead of under the fire .

gases and liquids are similar in which they flow ,thus they are called fluids .

heat transfer carries hot fluids upwards and cold fluids downwards is called convection . :)

conduction

CONDUCTION

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

Thermal energy is transferred from a region of higher temp. to a lower temp. but the time interval that it is transferred varies on the type of medium being used.

thermal energy is transferred faster in a good conductor (eg. wood) but slower in a poorer conductor( insulator).

this reminds me of a joke. one day a conductor lost his baton hence uses a sword to conduct. during practice, a player was constanly playing out of tune and the conductor got very angry and threw the sword at the player. he killed the player and was sentence to death through a electric chair but survived. the law states that if a man is not dead by the electric chair after 3 times of shocking, he can be released. and one day, the conductor lost his baton again and the same thing happen and still survived the electric chair. Why is this so? it is because he was a bad conductor.



Heat travels up slowly through the wooden and plastic ladle and even faster through the metal ladle thus the metal ladle will feel heated faster compared to the wooden and plastic ladles.

Heat is transferred when molecules start to vibrate rapidly and bumping faster and faster into their slower"neighbors" causing them to speed up in turns . this process continues throughout the ladle ,the increase speed in vibration and therefore the heat is passed on to molecule to molecule or from atom to atom.

wood and plastic are bad conductors of heat
metal is a good conductor of heat :) conducts heat rapidly

why are metals good conductors?

Metal contains electrons that are not attracted to nucleus ,moving in a random motion. FREE ELECTRONS

Not only the atoms at the end of the ladle start to vibrate , the electrons also speed up and begin to move faster, colliding with the atoms more often and with more force.

Each time a free electron collides with an atom ,it causes that atom to vibrate a little faster.

The metals contain millions of those free electrons with collides with atoms and speed up the vibrations of atoms and the transfer of heat .

Thus non metals are bad conductors of heat while metals are better conductors of heat

thermal energy

Thermal energy is transferred from a region of higher temperature to a lower temperature.

Thermal energy is transferred by conduction,convection and radiation :)

A man was locked up in a freezer, there is difference in temperature between his body and the surrounding. Thus he will feel cold due to the loss in thermal energy to the surrounding cold air .

haha hehe hoho hahahehehoo

here is some random jokes:)

Q: At a garage sale, a electron and a proton cost $10 each. How much does a neutron cost?
A: free oF charge ( no charge)

Q: What did the thermometer say to a graduated cylinder.

A: You may have graduated but i still have more degrees than you.

one day hydrogen said,"someone has stolen my electron! i am positive." then oxygen said,"Oh i thought you are just being negative again."

chilly willy