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标题: Another Physics Problem [打印本页]

作者: QL 时间: 2005-10-1 19:59
标题: Another Physics Problem

我们知道，在凸透镜的一侧放一烧红的铁块，那么热辐射在另一侧会聚焦，焦点的温度会比周围要高。如果把烧红的铁块换为冰块，那么在另一侧焦点的温度是不是会比周围低？

作者: QFT 时间: 2005-10-1 22:10
标题: 回复：Another Physics Problem

the temperature of the focus is always higher.

作者: ob 时间: 2005-10-2 11:42
标题: I think the answer is no.

Cause the 凸透镜is focus the red light and infrared light on the other side. Ice does not emit infrared or red light.

作者: husonghu 时间: 2005-10-2 11:55
标题: Agree,.........

冰块无热辐射，That's the point.

作者: QL 时间: 2005-10-2 16:25
标题: 回复：Agree,.........

That is exactly the point. But the answer is yes.

A hint: under ordinary in-door condition on earth, there is radiation evenly from every direction...

作者: QFT 时间: 2005-10-2 21:08
标题: one further question

Will a piece of iron in contact with ice radiate light?

作者: QL 时间: 2005-10-2 22:49
标题: 回复：one further question

I'm no physics major, my understanding is that every object with temperature above absolute zero will radiates light, but the intensity varies according to temperature.

作者: QFT 时间: 2005-10-3 01:19
标题: 回复：回复：one further question

yes, you are right. the intensity is proportional to T^4, where T is the temperature relative to absolute zero. The frequency of the emitted light also depends on temperature. The higher the temperature, the higher frequency of the light.

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