2.5 ENERGY TRANSFER 2 Learning Objectives: Describe some sources of infrared radiation. Explain how energy is transferred by radiation. Quick recap: What are the two methods of heat transfer we have learned about so far? Can you explain what’s happening in terms of particles? There are three methods of heat transfer: Yesterday’s lesson Today’s lesson RADIATION is a way of transferring heat, which does not need particles. The sun’s energy reaches the earth by radiation. Heat radiation from the sun is called SOLAR RADIATION or RADIANT HEAT. Radiation travels in straight lines. This is called a radiator because it radiates heat. ABSORBS heat radiation, the When an object _________ heat energy is transferred to the object. The object heats up. REFLECTS heat radiation, the When an object _________ heat energy bounces off the object and is not transferred to the object. The object does not heat up. EMITS heat radiation, heat When an object _________ from the object is transferred to the surroundings. The more heat radiation is absorbed by an object, the hotter the object gets. Different types of surface absorb different amounts of heat. Pale or silver surfaces DO NOT absorb much heat radiation, because they reflect heat radiation well. They also don’t emit heat radiation very well. Why do you think marathon runners are given silver blankets after the race? How do you think cricket players keep cool by wearing white? Why do you think some buildings in hot countries are painted white? Dark, dull surfaces absorb heat radiation well. They also emit heat radiation well. They do not reflect heat radiation very well. Why do you think the inside of an oven is painted black, not white? Why do you think cats prefer sleeping on black cars than white cars? So, what do you think is going to happen in our experiment? Shiny or pale surfaces Dull or dark surfaces Good absorbers of heat? NO YES Good emitters of heat? NO YES Good reflectors of heat? YES NO Now you should take a new page in your book and prepare a large summary of conduction, convection and radiation. Include diagrams! HOMEWORK: Complete the conduction, convection and radiation worksheet. Hand in just the sheet. http://www.teachertube.com/video/radiationconduction-and-convection-159713