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?

"Gary Helfert" wrote in message
. ..
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.



Crooke's radiometer.


My question is wheather this is true?

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


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?

See Newton's third law.

Dear Gary Helfert:

On Sep 24, 10:36*am, "Gary Helfert" wrote:
When I was a kid a remember a bulb shaped device
with a spinner inside supporting diamond shaped
paddles.

Crookes radiometer
.... if you want to do a Google search ...
http://en.wikipedia.org/wiki/Crookes_radiometer

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,

Not the cheap ones, with gases still in the "vacuum envelope".

rather it was the light warming the dark side of
the paddles repelling molecules of air inside the
bulb.

Yea, pretty much.

It was the repulsion due to warming that caused
to spinner to rotate.

My question is wheather this is true?

Yep. If the device has *very* good bearings, and no appreciable
gasses in the enveolpe, it will rotate white side away from the light
source. The black side absorbs the directed momentum, and radiates it
diffusely. The white side "reflects" the momentum back the way it
came (mostly). Of course painted surfaces emit about the same amount
of light regardless of "color", but a mirrior would not...

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.

A good idea for a vacuum. You might want to read "The Mote in God's
Eye" by Larry Niven, to imagine this implemented.

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?

Light carries momentum, momentum derived from the reaction that
emitted it. If light slams into something that absorbs or relfects
it, momentum will be exchanged / transferred.

So how did you imagine that had anything to do with wave particle
duality?

David A. Smith

"dlzc" wrote in message
...
Dear Gary Helfert:

On Sep 24, 10:36 am, "Gary Helfert" wrote:
When I was a kid a remember a bulb shaped device
with a spinner inside supporting diamond shaped
paddles.

Crookes radiometer
.... if you want to do a Google search ...
http://en.wikipedia.org/wiki/Crookes_radiometer

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,

Not the cheap ones, with gases still in the "vacuum envelope".

rather it was the light warming the dark side of
the paddles repelling molecules of air inside the
bulb.

Yea, pretty much.

It was the repulsion due to warming that caused
to spinner to rotate.

My question is wheather this is true?

Yep. If the device has *very* good bearings, and no appreciable
gasses in the enveolpe, it will rotate white side away from the light
source. The black side absorbs the directed momentum, and radiates it
diffusely. The white side "reflects" the momentum back the way it
came (mostly). Of course painted surfaces emit about the same amount
of light regardless of "color", but a mirrior would not...

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.

A good idea for a vacuum. You might want to read "The Mote in God's
Eye" by Larry Niven, to imagine this implemented.

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?

Light carries momentum, momentum derived from the reaction that
emitted it. If light slams into something that absorbs or relfects
it, momentum will be exchanged / transferred.

So how did you imagine that had anything to do with wave particle
duality?

David A. Smith
=================================================

Of course it does. Corks on waving water merely bob up and down,
surf riders come into the shore. When does a cork become a surf rider?

"Androcles" wrote in message
...

"Gary Helfert" wrote in message
. ..
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.



Crooke's radiometer.


My question is wheather this is true?

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


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?

See Newton's third law.



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?

Dear Gary Helfert:

"Gary Helfert" wrote in message
...
....
Could that laser canon on the moon really
supply the wind for a space sail?

"Wind" no, thrust yes.

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

David A. Smith

"Gary Helfert" wrote in message
...

"Androcles" wrote in message
...

"Gary Helfert" wrote in message
. ..
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.



Crooke's radiometer.


My question is wheather this is true?

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


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?

See Newton's third law.



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?

"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.
http://www.guardian.co.uk/science/20...man.yves.rossy

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

Hello Androcles:

On Sep 24, 3:14*pm, "Androcles" wrote:
"dlzc" wrote in message
...
....
So how did you imagine that had anything to do
with wave particle duality?

Of course it does. Corks on waving water merely
bob up and down, surf riders come into the shore.
When does a cork become a surf rider?

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

"dlzc" wrote in message
...
Hello Androcles:

On Sep 24, 3:14 pm, "Androcles" wrote:
"dlzc" wrote in message
...
....
So how did you imagine that had anything to do
with wave particle duality?

Of course it does. Corks on waving water merely
bob up and down, surf riders come into the shore.
When does a cork become a surf rider?

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?

"Androcles" wrote in message
...

"dlzc" wrote in message
...
Hello Androcles:

On Sep 24, 3:14 pm, "Androcles" wrote:
"dlzc" wrote in message
...
...
So how did you imagine that had anything to do
with wave particle duality?

Of course it does. Corks on waving water merely
bob up and down, surf riders come into the shore.
When does a cork become a surf rider?

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?





In physic class we were taught light was a wave but sometimes behaved as a
particle.
We covered much material about the wave nature of light but I don't remember
the
particle nature of light ever being discussed.
I assumed the light windmill worked because of the heating effect on the
dark surface.
After I was informed the device I was referring to is called Crookes
radiometer I was able to google it and find out light was
in fact behaving as a particle in that by bouncing off the mirrored surface
it imparted a force.
The heating effect explaination however was not wrong though. If you have an
incomplete vacuum in the bulb, the force repulsion of
air molecules off the hot surface (dark side) will exceed photon impingment
on the mirrored side.
As to my subject heading "Wave/Particle nature of light", wouldn't this be
an example of where light is acting like a particle?