And God said…

And God said, Let there be Maxwell’s Equations with boundary condition, and some electric charge but not magnetic charge: and there was light.

One year of the EM course takes the original parody into the next level, since Maxwell’s Equations along can not strictly describe the existence of EM waves – you’ll need charges to generate them, electric charges or magnetic charges – the later are “magnetic monopole” exists only in Maxwell’s theory but cannot be found in the real world. God just didn’t make any of them.

神說,要有馬克斯威爾方程式、邊界條件、電荷但是沒有「磁荷」,就有了光。

一年的電磁學課程把原版的笑話提升到全新的領域XD。

嚴格來說馬克斯威爾方程式本身不能解釋電磁波的存在,必須要有電荷或是「磁荷(magnetic charge)」產生電磁波,其中磁荷卻又是理論上存在但是在真實世界中找不到的磁單極。上帝可能覺得電荷就夠用了吧。

喔,原版的句子是「神說,要有光,就有了光。」,創世紀 1:3。

Wave Pocket

Wave Pocket Animation

這是用Maplesoft Maple做的波包動畫Demo,要看會動的版本請按All Sizes(警告:700k GIF)。從動畫可以看出來波包以群速度向+x的方向移動,而且隨著時間能量慢慢的散開。

相對於波包在物理中的重要意義,波包的數學相當簡單;近代物理中的物質波、電磁波波速與能量傳播的速度的關係都與波包有關係。

This is an animation generated by Maplesoft Maple. See it in action in the All Sizes page (Warning: 700k GIF). You can see it travels in group velocity, and the energy decays from time to time.

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