f.3 phy! about conduction,,how to explain?

用戶97935

2008-06-02 12:53 am

1.A piece of paper is wrapped around the rod and the rod is then held over a flame. It is found that the paper in direct contact with wood burns but the paper in contact with the copper does not. Explain the phenomenon briefly.

2.Jane has ordered a glass of iced water with lemon. The plastic straw and the mental spoon are put into thw water at the same time. After a moment , Jane finds that the upper end of the spoon is munch colder than that of the plastic straw. Suggest two properties of the spoon to account for the phenomenon.

回答 (1)

用戶235974

2008-06-03 11:14 pm

✔ 最佳答案

1. It is because copper is a better thermal conductor than wood.

When being put over a flame, copper absorbs heat faster than paper
does so much heat from the flame is absorbed by copper. Only a small
amount of heat is absorbed by paper. The temperature rise in paper
is not significant enough to ignite the paper.

When being put over a flame, wood absorbs heat as fast as paper does
so compared to the first case, paper absorbs more heat this time. So
paper's temperature rises more this time.
The temperature rise in paper is significant enough to ignite the paper.

2. Spoon is made of metal so it is a good heat conductor.
It transferrs heat from it to the iced water faster.
Spoon has a larger surface area than straw does so this provides
more area for heat transfer by conduction.

參考: myself

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