關於熱學的簡單物理問題

Tieria

2009-07-26 8:09 pm

1. A student was given the following information: ‘A cup of water of mass m is heated from 0 C to 100 C, then it starts to boil. The specific heat capacity of water is 4200 J kg^-1 C^-1.’ He calculated the specific latent heat of vaporization of water as follows.

∵ E = mcΔT and E = ml
∴ l = cΔT
= 4200 x 100
= 420000 J kg^-1

Is the student’s work right or wrong? Wrong.

※ 請詳細解釋錯的原因※

更新1:

「&becaus; E = mcΔT and E = ml」這裡的代碼有問題，「&becaus;」應解為「因為」。

回答 (1)

天同

2009-07-27 1:48 am

✔ 最佳答案

The reason is straight forward, the meaning of the two [E]s are not the same.
The first [E], in the equation E= mcΔT, is the energy required to raise the temperature of a mass m of water by ΔT.
The second [E], in the equation E = ml, is the energy required to evaporate a mass m of water at its boiling point.
You cannot equate the two equations because they are of different meanings.

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