{"id":633,"date":"2011-06-15T20:32:54","date_gmt":"2011-06-15T20:32:54","guid":{"rendered":"http:\/\/occamstypewriter.org\/rpg\/?p=633"},"modified":"2011-06-15T20:32:54","modified_gmt":"2011-06-15T20:32:54","slug":"on-the-hairy-nature-of-light%e2%80%94redux","status":"publish","type":"post","link":"https:\/\/occamstypewriter.org\/rpg\/2011\/06\/15\/on-the-hairy-nature-of-light%e2%80%94redux\/","title":{"rendered":"On the hairy nature of light\u2014redux"},"content":{"rendered":"

A while ago I reported on an experiment. Using my laser beam I demonstrated the wave nature of light<\/a>, by measuring its diffraction. One of the referees, for reasons of poetry, wanted to see the experiment repeated with a different wavelength laser. <\/p>\n

So, like a good little peer-reviewed scientist I toddled off and repeated the experiment with a red laser beam that very evening. And here, finally, are the results. No surprises: the red laser was refracted more than the green one. About 20% more, which is what I’d have predicted given the difference in rated wavelengths.<\/p>\n

But here are the pictures, and the maths. The working for the green laser is given in my earlier post<\/a>.<\/p>\n

First, here’s the experimental set up:<\/p>\n

\"Laser<\/a><\/p>\n

Note the high-tech use of a peg and Scotch Tape to hold the hair (human, brunette) in place. There’s also a slightly fuzzy photo, taken under ambient light (one of those dreadful energy-saving bulbs) in which you can see the beam itself<\/a> thanks to Rayleigh scattering and the dust in the spare room.<\/p>\n

\"Green<\/a>
\nMeasuring the green laser<\/em><\/p>\n

For the red laser, I had to turn off the lights (it only being rated at 1 mW); I also bounced it off a mirror to give me a longer path length and therefore a better node measurement.<\/p>\n

\"Red<\/a><\/p>\n

Using this method, I measured the third maximum at 13 cm from the central spot. I measured the path length at 6.75 m. Given<\/p>\n

nλ = xd\/L
\nwhere <\/p>\n

n = # of maximum
\nx = distance of maximum
\nd = slit distance (i.e. the hair width–approximately 100 microns)
\nL = length of beam<\/p>\n

then <\/p>\n

nλ = (0.13 m 100 x 10-6<\/sup> m) \/ 6.75 m<\/p>\n

so <\/p>\n

λ = (1.9259 x 10-6<\/sup> m) \/ 3<\/p>\n

therefore the wavelength is 642 nm<\/strong>. <\/p>\n

QE, as they say, D.<\/p>\n

\"Green<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

A while ago I reported on an experiment. Using my laser beam I demonstrated the wave nature of light, by measuring its diffraction. One of the referees, for reasons of poetry, wanted to see the experiment repeated with a different … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[34],"tags":[94,122,123],"class_list":["post-633","post","type-post","status-publish","format-standard","hentry","category-science","tag-laser","tag-light","tag-wave"],"_links":{"self":[{"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/posts\/633","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/comments?post=633"}],"version-history":[{"count":0,"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/posts\/633\/revisions"}],"wp:attachment":[{"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/media?parent=633"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/categories?post=633"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/occamstypewriter.org\/rpg\/wp-json\/wp\/v2\/tags?post=633"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}