Radio waves vs light waves

Katherine,

Physicists call it "radiation pressure" and it's
measureable in a lab.


you can drive spaceships with it, though. There's a great scifi story
by Arthur C. Clarke about a solar yacht race using radiation pressure
from the sun on big "sails".

--
Thomas Borchert (EDDH)

On Thu, 19 Feb 2004 13:17:36 +0100, Thomas Borchert
wrote:

Katherine,

Physicists call it "radiation pressure" and it's
measureable in a lab.


you can drive spaceships with it, though. There's a great scifi story
by Arthur C. Clarke about a solar yacht race using radiation pressure
from the sun on big "sails".

I've always wondered about the following:

Ok - so we all agree that a light puts out a small amount of force.
Newton tells us that an equal an opposite amount of force would be
directed in the opposite direction. F=ma.

So why can't we use high-intensity lights powered by a nuclear reactor
as a source of space propulsion? Is the F so small and the 'm' so
large that the 'a' would be miniscule? There's no wind resistance to
overcome in space, so you don't have to fight against that. I imagine
gravity would still be a factor though.

-Nathan

So why can't we use high-intensity lights powered by a nuclear reactor
as a source of space propulsion?


They can. But the F is small, so you need a lot of t to reach much of a v, as
long as you are far enough from a g.

Such systems have only been developed in science fiction however because we are
not yet doing enough interstellar travel, and people are uncomfortable with
nuclear reactors in space.

Jose

--
(for Email, make the obvious changes in my address)

"Teacherjh" wrote in message
...

So why can't we use high-intensity lights powered by a nuclear reactor
as a source of space propulsion?


They can. But the F is small, so you need a lot of t to reach much of a
v, as
long as you are far enough from a g.

Such systems have only been developed in science fiction however because
we are
not yet doing enough interstellar travel, and people are uncomfortable
with
nuclear reactors in space.

Here is something interesting Jose.

Although light is not conducted like RF, light behaves very much like RF in
a wave guide.

Although light is not conducted like RF, light behaves very much like RF in
a wave guide.


In a wave guide appropriate to light frequency, or to radio frequency?

Jose

--
(for Email, make the obvious changes in my address)

"Teacherjh" wrote in message
...

Although light is not conducted like RF, light behaves very much like RF
in
a wave guide.


In a wave guide appropriate to light frequency, or to radio frequency?

The size of waveguide is frequency dependant, but the EM characteristics of
light require only a difference of scale. Propigation is still a factor for
materials inside a waveguide though. So as to say, insulator materials may
act differenty to light than RF.

The size of waveguide is frequency dependant...

Then what, new, are you saying? Light is just like RF, just a different F,
therefore a different scale to see the effects. They have already made
antennas that emit light - they are very small, but they work the way radio
antennas work. I'd be surprised if a suitably scaled wave guide (of an
appropriate material) did NOT work with visible light.

I'm also not sure what you mean by:

Although light is not conducted like RF

Jose


--
(for Email, make the obvious changes in my address)

"Teacherjh" wrote in message
people are uncomfortable with nuclear reactors in space.

Well, uncomfortable with getting them there, actually.

--
Jim Fisher