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Fun with physics
07-13-2018, 11:08 PM,
#1
Fun with physics
Apparently, my recent post explaining rainbows was too much for a number of searchers at another forum. I could derive the equation for the angles of reflection of both the primary and secondary rainbows (a common problem from our doctoral prelims), but that requires an understanding of geometry and trig, which I suspect is way beyond the collective brain matter in that other forum.

Alternatively, I thought I would suggest an experiment that all of you - especially those with kids - will really enjoy. The next time there is a full moon (July 27) and you have clear skies, take a piece of window screen and hold it up to look at the moon through the screen. Ta-da! The pattern you see is an excellent example of diffraction as well as the better known Zia symbol. Now, rotate the screen. The pattern of smeared light will rotate with the screen. The wires in the screen are breaking up the light of the moon (diffractio from the Latin for break up) in directions that are perpendicular to the wires. Fun, huh?

By the way, diffraction is the reason that the light from your flashlight will only travel so far. I found the zoom capability in the following flashlight very helpful in probing the areas under rocks and in crevices.

https://www.amazon.com/Portable-Handheld...lashlights

Good luck and stay safe!
Reply
07-13-2018, 11:20 PM, (This post was last modified: 07-13-2018, 11:22 PM by antigroove.)
#2
RE: Fun with physics
Thanks for the info! Is there any way to increase the apparent illumination of a flashlight or headlamp into dark areas while standing in bright ones (assuming fixed lumens)? Maybe red or green shift or something?
Reply
07-13-2018, 11:35 PM,
#3
RE: Fun with physics
(07-13-2018, 11:08 PM)brubr Wrote: Apparently, my recent post explaining rainbows was too much for a number of searchers at another forum. I could derive the equation for the angles of reflection of both the primary and secondary rainbows (a common problem from our doctoral prelims), but that requires an understanding of geometry and trig, which I suspect is way beyond the collective brain matter in that other forum.

Alternatively, I thought I would suggest an experiment that all of you - especially those with kids - will really enjoy. The next time there is a full moon (July 27) and you have clear skies, take a piece of window screen and hold it up to look at the moon through the screen. Ta-da! The pattern you see is an excellent example of diffraction as well as the better known Zia symbol. Now, rotate the screen. The pattern of smeared light will rotate with the screen. The wires in the screen are breaking up the light of the moon (diffractio from the Latin for break up) in directions that are perpendicular to the wires. Fun, huh?

By the way, diffraction is the reason that the light from your flashlight will only travel so far. I found the zoom capability in the following flashlight very helpful in probing the areas under rocks and in crevices.

https://www.amazon.com/Portable-Handheld...lashlights

Good luck and stay safe!

This sounds fun, thanks. Would this be better to do in the mountains or in the city?
Reply
07-13-2018, 11:48 PM, (This post was last modified: 07-13-2018, 11:50 PM by brubr.)
#4
RE: Fun with physics
(07-13-2018, 11:20 PM)antigroove Wrote: Thanks for the info! Is there any way to increase the apparent illumination of a flashlight or headlamp into dark areas while standing in bright ones (assuming fixed lumens)? Maybe red or green shift or something?

Actually, that's why I love the zoom on the flashlight I mentioned. Truly, its awesome, even in bright light. Because the background scattering is interfering with your eyes viewing of the light from the flashlight, a zoom capability is the best way to go. I was dubious at first, but this little light convinced me.

(07-13-2018, 11:35 PM)Bet Wrote:
(07-13-2018, 11:08 PM)brubr Wrote: Apparently, my recent post explaining rainbows was too much for a number of searchers at another forum. I could derive the equation for the angles of reflection of both the primary and secondary rainbows (a common problem from our doctoral prelims), but that requires an understanding of geometry and trig, which I suspect is way beyond the collective brain matter in that other forum.

Alternatively, I thought I would suggest an experiment that all of you - especially those with kids - will really enjoy. The next time there is a full moon (July 27) and you have clear skies, take a piece of window screen and hold it up to look at the moon through the screen. Ta-da! The pattern you see is an excellent example of diffraction as well as the better known Zia symbol. Now, rotate the screen. The pattern of smeared light will rotate with the screen. The wires in the screen are breaking up the light of the moon (diffractio from the Latin for break up) in directions that are perpendicular to the wires. Fun, huh?

By the way, diffraction is the reason that the light from your flashlight will only travel so far. I found the zoom capability in the following flashlight very helpful in probing the areas under rocks and in crevices.

https://www.amazon.com/Portable-Handheld...lashlights

Good luck and stay safe!

This sounds fun, thanks. Would this be better to do in the mountains or in the city?

It will work anywhere the moon is nice and bright. I first tried it in Tucson 30 years ago, but it will work anywhere.
Reply
07-14-2018, 01:27 AM,
#5
RE: Fun with physics
Thanks for the response! My FIL got me a Browning Maxus headlamp that is incredibly bright. It holds its own against my big maglite even.
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