退出前倒數最後五個發問 ~ conduction , convection 和 radiation 有何分別？
conduction , convection 和 radiation 有何分別？
- 1 十年前最愛解答
need medium object,heat is transfer from the hot part to the cold part.
e.g a cotton jacket keeps warm by trapping air next to the body.
cotton jacket as a medium.
heat can be transfer in a fluid (liquid or gas),the heated fluid expands rise and replaced by the by the surrounding coller fluid .there will produce a convention current.
e.g.boil the water. / wind and sea breezes.
water as a fluid medium./ air as a medium.
energy is gained on absorbing infar-red radition from object,no need to use a medium.
it can be transfer haet in a vacuum
e.g sunlight has travel through the space before reaching the earth.
事實上vaccum flask 可以有齊以上3種原理.
1)cork stopper reduces heat loss by conduction and convention
2)outer case and the silver wall inside is always silver in colour,reduce heat loss by radition
3)vacuum flask (the vacuum between the double glass walls reduce heat loss by conduction and convention)
2006-12-16 20:24:43 補充：