10) Radiation
When you step outside into bright sunlight, you feel the warmth of the Sun on your skin. The heat of the Sun cannot reach you by conduction or convection because space is a vacuum. There are no particles between the Sun and the Earth to pass vibrations or move in convection currents. The heat transfer from the Sun to the Earth is called Radiation.
1) Learning about Radiation:
Radiation is the transfer of heat energy by invisible waves called "Electromagnetic Waves". These waves do not need a material to travel through. Heat radiation is sometimes called infra-red radiation. All electromagnetic waves travel at the speed of light and there are a whole range of different types of electromagnetic waves such as Radio, visible light, ultraviolet, x-rays and gamma rays. Watch this video about electromagnetic waves. All objects give out heat radiation - the hotter the object, the more heat it radiates. Also dark objects tend to radiate more heat than shiny or light coloured ones at the same temperature. When infra-red radiation hits something, it can be: 1) absorbed into the object, warming it up or changing its state 2) reflected off the object 3) transmitted through the object |
3) Review Questions on Radiation:
A) Identify the type of heat transfer that applies in each case below: i) no material is required. ii) particles vibrate iii) particles move through a material B) Identify a household device that gives out both light and radiated heat. C) A saucepan full of water is heated on a stove. Analyse the situation and explain the different types of heat transfer that is happening |
Extension Task: Test your knowledge of heat transfer methods by answering the questions in this interactive quiz
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