Heat Transfer
Heat Transfer #2
"How to toast bread!" When a piece of bread is put in a toaster the wires inside the toaster glow red hot on either side of the bread.
How does the heat energy get to the bread?
Is it by conduction?
No, the heat energy cannot conduct through the air to the bread because air is a very bad conductor.
Is it by convection?
No, hardly any of the heat energy could have travelled to the bread by convection, as the hot air particles would rise out of the toaster.
The heat energy must have reached the toast some other way. It travelled as radiated heat. This heat energy movement is sometimes called heat waves, but strictly speaking, it is infrared radiation.
Hot objects radiate heat to their colder surroundings. The weird thing is that the surface colour of an object makes a difference.
Black and dull surfaces emit (give out) and absorb radiation well.
White and shiny surfaces do not emit radiation well and reflect radiation instead of absorbing it.
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