Source & single slit

2011-04-10 7:23 pm

圖片參考：http://imgcld.yimg.com/8/n/HA00270495/o/701104100038513873424040.jpg
fig.1

We always consider it is a pt. source when the slit width ,a almost= wavelength of the incident wave .From above fig.1, it is in the top view angle,

圖片參考：http://imgcld.yimg.com/8/n/HA00270495/o/701104100038513873424041.jpg
fig.2

But however,as it is a 'slit' ,the wave arrive the slit should be fig.2 shown,

Q1 : How should I explain althought in the sources presence in fig.2 shown,it is still right for the def. of pt. source hence in the double slits experiment which acts as a source slit?

圖片參考：http://imgcld.yimg.com/8/n/HA00270495/o/701104100038513873424052.jpg

This time if I replace the slit in 'a hole' and it have diameter a,which is the same in magnitude to the silt width a,which shown in fig .1 ,and other conditions are also the same as fig .1,

Q2 : Will diffraction pattern form in this situation ?If yes ,will it be similar to Newton's Rings?

THX for ans!!

回答 (1)

天同

2011-04-10 9:15 pm

✔ 最佳答案

Q1 : How should I explain althought in the sources presence in fig.2 shown,it is still right for the def. of pt. source hence in the double slits experiment which acts as a source slit?

If you only limit yourself to two dimensions, each point source in fig.2 would produce a pattern. A line source, which is a source that made up of a vertical array of points, would then produce vertical bands of bright and dark fringes, as what is observed in the double-slit experiment.

Q2 : Will diffraction pattern form in this situation ?If yes ,will it be similar to Newton's Rings?

You could see the interference pattern of a hole on the following web-page. The pattern can be seen near the middle of the page.

http://www.itp.uni-hannover.de/~zawischa/ITP/diffraction.html

2011-04-10 13:32:31 補充：
Just to correct a typo. The first sentence in the answer to Q1, "If you only limit yourself to ONE dimension,..."

2011-04-10 13:34:53 補充：
Be aware that in the double-slit experiment, the slit width is assumed to be infinitely small. In practice, it should be smaller than or at least equal to the wavelength of light used. Otherwise, the "poin-source" assumption would not hold.

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