Friday, November 30, 2007
Blip
An ephemeral life we have,
and an interesting bit of complexity therein!
Mesmerised you are by dualities,
over it will be by the next bat of the eyelid!
and an interesting bit of complexity therein!
Mesmerised you are by dualities,
over it will be by the next bat of the eyelid!
Thursday, October 25, 2007
Blue skies!
Recently, the Optical Society of America opened a chapter at Caltech and organized an outreach program to give demonstrations in optics to girl scouts, roughly in classes 6-9. So one particularly warm afternoon (thanks to the greenhouse effect stemming from the fires in Southern California) we set out to an elementary school in neighbouring Alhambra. It was a rather odd configuration that we came across: four of us "teachers", four girl scout organisers and two students!
One of the demonstrations involved explaining why the sky appears blue during the day and reddish during sunset time. The organisers had a "manual" that outlined explanations of the demos. This had some rather misleading analogies, such as "energetic photons travel shorter distances, much as if you were to start running very fast, you would tire out sooner." Instead of dwelling further on these so called explanations, I thought of attempting a simpler explanation.
If one were to imagine a large, tranquil body of water such as a lake which has a little wooden post sticking out in the middle. Now think of two scenarios. In both of them, there are (plane) waves travelling in the water toward the post.
In the first case you have waves of long wavelengths (distance between consecutive peaks (or valleys) of a wave) that don't really "see" the post since each wave is much longer than the size of the post and so carry on almost unhindered past the post.
In the second case you have waves of shorter wavelengths (comparable with the size of the post) and thus get disturbed (scatter) appreciably and spread out after hitting the post. Qualitatively, this explains why shorter wavelengths scatter more than longer wavelengths.
Thus, during most of the day time, the blue components of sunlight (short wavelengths) scatter more and "spread" out, giving the sky the blue colour. Analogously, during sunset time, the blue wavelengths scatter all right, but since the sun's rays have to travel through a thicker layer of atmosphere to reach us now , these scattered blue wavelengths eventually get absorbed (loosing energy after multiple scattering events). What remains are the red wavelengths; ergo, the sky appears reddish at sunset.
The technical explanation of the same involves something known as Rayleigh scattering where the scattering cross section has a strong wavelength dependence ( wavelength^{-4} ) which implies that shorter (blue) wavelengths get scattered more than longer (red) wavelengths. This originated from the Tyndall effect . Here, if one shone light through a transparent glass of water mixed with a little milk and observed it straight-on from the opposite side, one would observe a slightly reddened colour, while if one observed the water from the side, one would see a slight blueish tinge to the light. (This effect was formalised by Lord Rayleigh soon after.) Contrary to popular belief, the scattering that causes the colours of the sky are due to the scattering of light by Oxygen and Nitrogen molecules, not dust particles, something Einstein calculated in 1911.
What I like about the waves in the water analogy is that it doesn't needlessly invoke the particle nature of light (I can't think of an explanation of this effect thinking of light as a particle) & it gives an intuitive sense of the wavelength dependence of scattering.
ps: This, I couldn't resist: Said the young man to the sunset, where are my blues ?!
One of the demonstrations involved explaining why the sky appears blue during the day and reddish during sunset time. The organisers had a "manual" that outlined explanations of the demos. This had some rather misleading analogies, such as "energetic photons travel shorter distances, much as if you were to start running very fast, you would tire out sooner." Instead of dwelling further on these so called explanations, I thought of attempting a simpler explanation.
If one were to imagine a large, tranquil body of water such as a lake which has a little wooden post sticking out in the middle. Now think of two scenarios. In both of them, there are (plane) waves travelling in the water toward the post.
In the first case you have waves of long wavelengths (distance between consecutive peaks (or valleys) of a wave) that don't really "see" the post since each wave is much longer than the size of the post and so carry on almost unhindered past the post.
In the second case you have waves of shorter wavelengths (comparable with the size of the post) and thus get disturbed (scatter) appreciably and spread out after hitting the post. Qualitatively, this explains why shorter wavelengths scatter more than longer wavelengths.
Thus, during most of the day time, the blue components of sunlight (short wavelengths) scatter more and "spread" out, giving the sky the blue colour. Analogously, during sunset time, the blue wavelengths scatter all right, but since the sun's rays have to travel through a thicker layer of atmosphere to reach us now , these scattered blue wavelengths eventually get absorbed (loosing energy after multiple scattering events). What remains are the red wavelengths; ergo, the sky appears reddish at sunset.
The technical explanation of the same involves something known as Rayleigh scattering where the scattering cross section has a strong wavelength dependence ( wavelength^{-4} ) which implies that shorter (blue) wavelengths get scattered more than longer (red) wavelengths. This originated from the Tyndall effect . Here, if one shone light through a transparent glass of water mixed with a little milk and observed it straight-on from the opposite side, one would observe a slightly reddened colour, while if one observed the water from the side, one would see a slight blueish tinge to the light. (This effect was formalised by Lord Rayleigh soon after.) Contrary to popular belief, the scattering that causes the colours of the sky are due to the scattering of light by Oxygen and Nitrogen molecules, not dust particles, something Einstein calculated in 1911.
What I like about the waves in the water analogy is that it doesn't needlessly invoke the particle nature of light (I can't think of an explanation of this effect thinking of light as a particle) & it gives an intuitive sense of the wavelength dependence of scattering.
ps: This, I couldn't resist: Said the young man to the sunset, where are my blues ?!
Tuesday, August 22, 2006
Ustad
From a news report:Oh life, who are you? You blow through the passages of the shehnai in glorious rhythm. Your tune ushers in the nation's independence, your melody brings men and women together in wedlock. A neem tree was your companion for many years, and while the world was still waking up to your genius, the leaves of the neem were dancing in an unchained melody. Now that you are in some other world, the tree grieves, much as the parents who left you long ago would have. With every riffle shot, the neem tree cries tears of leaves, for its loyal son is no more. As is said; "अपने ही पानी मे घुल जाना बर्फ का मुकद्दर होता है।"
Varanasi: Thousands bid an emotional farewell to shehnai maestro Ustad Bismillah Khan whose mortal remains were laid to rest at the Karbala-Fatamaan burial ground in Varanasi.
Men of the 1/11 Gorkha battalion lowered their muffled weapons as a mark of respect to the departed soul. The troops saluted the Bharat Ratna awardee by firing 36 blank rounds in the air even as buglers paid the Last Post. Before the burial, a majlis was held at the grounds in which prayers were offered for the peace of the departed soul. The burial, incidentally, took place under a neem tree just by the side of the place where Khan Saheb used to sit and play the shehnai during the 5th and 8th day of Moharram. Earlier, in the evening, people had queued up all along the two-kilometre road through which he had gone to express his 'Aasu Ka Nazrana' by playing shehnai during the 5th and 8th day of Moharra
---
Thursday, July 13, 2006
If it weren't for CNN-IBN ...
Ref: http://clients.ibnlive.com/features/mumatt/
This kind, charitable news agency, an Indian version of CNN, very graciously offers to donate 1 Rupee for every "e-candle" that is lit on their website to the relief of victims of "Terrible Tuesday." So although they seemed to be very moved by the tragedy and this that, and have some money to offer to its victims, it wants you to log on to their site, provide them with your name, email and phone no., and only then will it donate this huge sum of money.
Mr. Rajdeep Sardesai and CNN-IBN, kindly go to hell.
This kind, charitable news agency, an Indian version of CNN, very graciously offers to donate 1 Rupee for every "e-candle" that is lit on their website to the relief of victims of "Terrible Tuesday." So although they seemed to be very moved by the tragedy and this that, and have some money to offer to its victims, it wants you to log on to their site, provide them with your name, email and phone no., and only then will it donate this huge sum of money.
Mr. Rajdeep Sardesai and CNN-IBN, kindly go to hell.
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