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Wave/Particle nature of light question.

Wave/Particle nature of light question. - Physics Forum

Wave/Particle nature of light question. - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 09-24-2008, 05:36 PM
Gary Helfert
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Default Wave/Particle nature of light question.



When I was a kid a remember a bulb shaped device with a spinner inside
supporting diamond
shaped paddles. The paddles were light colored on one side & dark on the
reverse side.
When light struck the paddles the spinner started rotating. I'm sure most of
you have seen this toy.

It was explained to me that it was not the light directly imparting the
rotation to the spinner, rather
it was the light warming the dark side of the paddles repelling molecules of
air inside the bulb.
It was the repulsion due to warming that caused to spinner to rotate.

My question is wheather this is true?
Discovery channel had a presentation on space propulsion where a laser
cannon on the
moon provided the energy to propel a craft using a space sail. This
explanation seems to
imply that light can impart a force on a target. What gives?
If a laser is fired in space is there a reactive force?

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  #2  
Old 09-24-2008, 06:27 PM
Androcles
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Default Wave/Particle nature of light question.


"Gary Helfert" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]. ..



Crooke's radiometer.


Evacuate the bulb so there are no air molecules to find out.
Whether the weather will fine or not, it will never be "wheather".



See Newton's third law.


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  #3  
Old 09-25-2008, 01:46 AM
Gary Helfert
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Default Wave/Particle nature of light question.


"Androcles" <Headmaster@Hogwarts.physics> wrote in message
news:bEvCk.73073$0i5.16723@newsfe11.ams2...

Yes, Crooke's radiometer is what I'm referring to. I did the google search
and it appears light can
exert pressure on an object. The article said it was minicule but the
radiometer had a surface area of a few
square inches. The pressure of current ion propulsion engines is the same as
a mouse fart yet it can propel
spacecraft over 100,000 mph. I guess my question now is weather light can
produce any practical level of thrust.
The space sails I have read about I assume use the solar wind which is not
the same as light. Could that laser
canon on the moon really supply the wind for a space sail?

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  #4  
Old 09-25-2008, 02:42 AM
N:dlzc D:aol T:com \(dlzc\)
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Default Wave/Particle nature of light question.

Dear Gary Helfert:

"Gary Helfert" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...
....

"Wind" no, thrust yes.

Just in case you are interested, tiny latex spheres are lifted
and moved by laser beams...

David A. Smith


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  #5  
Old 09-25-2008, 01:35 PM
Androcles
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Default Wave/Particle nature of light question.


"Gary Helfert" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

"Practical" is a rather funny word, it depends on many factors.
This bird produces enough fart to lift its own weight:
http://admin.royalnavy.mod.uk/upload...Harrier002.jpg
Few other aircraft can do that, but they are still practical for flying
passengers.
"Fusionman" cancelled his flight on four butterfly farts across the English
Channel
today because of weather.
[Only registered users see links. ]

Light will produce "enough" thrust if there is "enough" light. You decide
what "enough" means.



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  #6  
Old 09-25-2008, 05:26 PM
dlzc
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Default Wave/Particle nature of light question.

Hello Androcles:

On Sep 24, 3:14*pm, "Androcles" <Headmas...@Hogwarts.physics> wrote:
....

Perhaps you failed to notice that multiple corks tend to agglomerate,
or disperse also. They also end up on the shore. Your similes aren't
doing you much good here.

I am asking the OP how his question relates to particle duality, since
the Crookes radiometer works on heating gasses in the envelope (and he
knew this). Can you let him answer?

David A. Smith
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  #7  
Old 09-25-2008, 06:00 PM
Androcles
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Default Wave/Particle nature of light question.


"dlzc" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...
Hello Androcles:

On Sep 24, 3:14 pm, "Androcles" <Headmas...@Hogwarts.physics> wrote:
....

Perhaps you failed to notice that multiple corks tend to agglomerate,
or disperse also. They also end up on the shore. Your similes aren't
doing you much good here.

I am asking the OP how his question relates to particle duality, since
the Crookes radiometer works on heating gasses in the envelope (and he
knew this). Can you let him answer?

David A. Smith

============================================
I'm not preventing him from answering, Smiffy. I asked YOU
at what point a cork becomes a surf rider.
The answer is when the water gets shallower, otherwise it drifts
with the tide. In other words ocean waves are essentially standing
waves except near shorelines, and the direction of energy transfer
is toward the shore -- even for an island.
Now... does a Crooke's radiometer turn if you evacuate the bulb?





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  #8  
Old 09-25-2008, 09:35 PM
Androcles
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Default Wave/Particle nature of light question.


"Gary Helfert" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]. ..


Yes, but Nature doesn't always agree with what you were taught - especially
what your tutor may read to you from a text book. Science has always been
full of surprises and teachers are not scientists... or they wouldn't be
teachers.
Consider a spinning pellet fired from a spud gun:
http://www.spudtech.com/images/products/sch80rifled.jpg
Seen sideways on, the helix is a wave:
http://www.androcles01.pwp.blueyonde.../AC/Photon.gif
That is a wave. Spinning potatoes have wave/particle duality.


Then you should discuss it. You'll be surprised what it will reveal.


Never assume anything. Assume makes an ass- out of -u- and -me, and
I'm no ass.


What happens if you have a complete vacuum?


Light always acts as a particle. It travels in straight beams, doesn't
spread
like waves on water or sound waves:
http://www.androcles01.pwp.blueyonde...ave/ripple.gif

You wouldn't say a shower of rain was a wave, would you?
Yet if the raindrops are spinning then they trace a wave.
Is this particle a wave?
[Only registered users see links. ]

It's a wave in TIME, it's not a wave in space.


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  #9  
Old 09-26-2008, 12:12 AM
N:dlzc D:aol T:com \(dlzc\)
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Default Wave/Particle nature of light question.

Dear Gary Helfert:

"Gary Helfert" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]. ..
....

It doesn't have to. As I said to you, lasers are used to lift
and position tiny latex balls. Additionally, photons are used to
alter the trajectory of charged particles.


Well, that is the first blush theory. But I don't find that
anyone has made such a device with essentially no gas, and got it
to turn in the direction necessary to support particle theory.


Not "repulsion", but "rebound" or "conservation of momentum".


Not when it is only heating a surface. Try Googling
"photoelectric effect"

It is better not to consider light as having either property /
behavior, since those "results" are a function of the test you
use to detect light. Better to realize that light is discrete
(particle model), and in groups Maxwell's equations (wave model)
work very well. Macroscopic beings like us have trouble trying
to impress "like ocean waves" or "like billiard balls" on
something like a quantum of light. Because Nature stands by
laughing at us...

David A. Smith


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  #10  
Old 09-26-2008, 04:04 AM
Gary Helfert
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Default Wave/Particle nature of light question.


"Gary Helfert" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]. ..
I don't want the discussion to get too theoretical. The last two lines of
the first paragraph of link [Only registered users see links. ]
states in a complete vacuum Crooks Radiometer would rotate with mirrored
surface moving away from the incoming beam. At this point I am just curious
how much pressure are we talking about? How does it compare to the solar
wind? If the light emitted from the sun were blocked out, would the earth
start drifting into a lower orbit around the sun? Any ideas here? I would
also like to thank you all for taking the time to try and answer my
questions.

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