當琴玄震動時形成駐波，這個時候它的相速是0.但是它的群速不是0.晶體中的光的相速可以超出光速。但群速不會。

來源: 桃花源主於 2018-11-07 06:30:35 [博客] [舊帖] [給我悄悄話] 本文已被閱讀：次

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