Question

Explain why the diffraction pattern of the hair appears in the horizontal direction that it does.

Answer 1

Well its a bit of a trending one . Lets begin..

​​​​​​​In a very obvious way , you must be aware of the diffraction phenomena of light which says that when it encounters an obstacle , it diverges in all direction in such a way that the rays interfere with each other . AS the theory of interference pattern goes in a way is called DIFFRACTION PATTERN. To be more distinct here we are using only a single slit unlike in interference when we use two such.

Now coming to question, when we take hair like structure {we will take bundle of hairs ofcourse they are extremely thin } , the light will bent across the hairs considering it at as an obstacle which is placed vertically . As mentioned earlier, depending upon the positions of CReSTS & TRUoGHS the minima [when crest and trough overlaps,darkness appears] and maxima [when same crest-crest or trough-trough overlaps,brightness appears] is formed . BUT IN SUCH A WAY THE diffraction pattern should be VERTICAL , but I am afraid its not !

Actually horizontal pattern appears because the light waves get diffracted by the very tip also. And it does not behave like single slit anymore . Due the Huygen's principle ,the secondary wavelets formed around the edges of the thin hair is HORIZONTAL . IT would not have been happend if the hair is not so thin so that the wavelets are horizontaly spread and they further interfere to form horizontal pattern of diffraction. This is the reasonable answer to your question .

Be safe AND thank you !