Radiation

Defination:

Radiation is the continual emission of infrared waves from the surface of al bodies, transmitted without the aid of a medium.
Radiation can occur at any temperature.

Since radiation does not need a medium for energy transfer. This means that radiation can take place anywhere, anytime. It's taking place RIGHT NOW!

Dull, black surfaces absorb infrared radiation faster compared to shiny, white surfaces
Dull, black surfaces EMIT infrared radiation faster compared to shiny, white surfaces

Conclusion:
A good emitter is a good absorber.
A poor emitter is a poor absorber

Reason:
Good absorber reflects LITTLE radiant heat.. and since lesser heat is reflected, the object will become hotter

Factors that affects the rate of reaction:
1. Colour and texture.
-Dull, black surfaces absorbs heat better and faster, unlike shiny white surfaces.
-Dull, black surfaces emits heat better and faster, unlike shiny white surfaces.

2. Surface Temperature
Though radiation takes place at any temperature, the higher the temperature of the surface of the object relative to the surrounding temperature, the higher the rate of infrared radiation.

3. Surface area
The larger the surface area, the rate of radiation is faster

You can remember the factors by:
Crazy Sadly Stupid
Crazy - Colours and texture
Sadly - Surface Area
Stupid - Surface Temperature

Here's some examples of radiation in this for this part of the chapter.

Well, Radiation helps us feel the heat from the sun. Withour radiation, no heat from the sun can reach us. Earth will no longer be a planet which is able to sustain life.

Radiation also helps us with those barbecue marshmellows that we all LOVE to eat. If we put the marshmellow in direct contact with the fire/flame, it will become brunt and we wont like that to happen right?! So, radiation helps to transfer the heat from the flame/fire to the marshmellow, melting it JUST ENOUGH


Another very good example of radiation is the Infrared thermometer

This is the device that most schools should have. I've used this before in school and at my tuition center.

No contact with the forehead is needed. It is placed like maybe 1-2 cm infront of your forehead and the thermometer only needs a scan to record the temperature. It's especially useful for this period of H1N1 as no contact is needed to measure the temperature of someone.

The Surfaces of kettles, teapots is also another example of radiation

The surface of kettles and teapots all has shiny surfaces to prevent heat from being absorbed. If kettle is made of dull black surfaces, the heat when the kettle is boiling would be absorbed by the surface, hence, taking a longer time for water to boil.

One last example that I'd like to state is the truck that transport fuel from a petroleum complex to petrol kiosks

The shiny surface of the truck is a poor absorber of thermal energy. Hence, when the truck is under hot sun, less thermal energy is absorbed and thus the increase in the temperature of the fuel in the tank is slowed down.

Last but not least, the video which I'll include frm Eureka

Episode 29 - Radiation Waves

Ch30 - Radiation Spectrum [explains why colours affect the rate of radiation]