F.3 phy questions

2011-06-05 1:19 am

1. In a vacum,there are no atoms or molecules.Explain why conduction does not oocure in a vacum.

2.Some stew pots made of stainless steel are copper plated.Explain how this design helps spread heat more evenly.(Hint: Stainless steel is not a very gd conductor compared to copper).

3.A polyfoam container is used to keep food warm
(a). Describe the heat flow in this case
(b). How can a polyfoam container keep food warm?
(c). What happens of a polyfoam container os folled woth cold food in summer?

回答 (1)

天同

2011-06-05 1:48 am

✔ 最佳答案

1. Conduction of heat takes place by transfer of molecular vibrations from one end of a material to the other end. In a vacuum, there is no material present, hence conduction of heat cannot take place.

2. Because copper conducts heat more rapidly than stainless steel, when the pot is heated, the heat at the bottom of the pot can be conducted rapidly by the copper to other parts of the part, thus helps to spread out the heat more evenly.

3.(a) Heat flow is mainly by conduction and radiation.

(b) Polyfoam contains plenty of small air sacks inside. Because air is a bad conductor of heat, hence heat loss from the container is prevented by the polyfoam.

(c) It could prevent heat to flow into the container from outside, thus keeping the food cold.

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