light and radio waves

[nec208]

Okay first I'm trying to grasp this concept.Take a candle you see light and walk away from the candle The light appears smaller and smaller has you move away to :mrgreen: you cannot see it at all.

The light does not get weak or despair it is just out side of your viewpoint. How can I understand this better and they go on that radio waves are like this too.


The stronger the candle or flash light the more light you will see or having a better eyeglasses will allow you to see the candle or flash light better.Than they go on saying radio waves are like this the more trasmitting power the more you will pick up or better the antenna the more you will picks up.

Then say the key is good antenna.The big dish antenna NASA uses take all the energy and concentrate the energy to center point.But does not really explain how it works.

I'm also trying to understand how NASA can pick up radio signals millions of light years away .

 

[MeteorWayne]

Unfortunately the translation into english makes your post gibberish.

Please try again.

If it helps, Radio and light are the same thing; they travel at the same speeds in the same manner. It's just different frequncies; we happen to have detectors (eyes) that work in a very small wavelength.

Please try again to ask the question you were aimang at!

 

[Mee_n_Mac]

Okay first I'm trying to grasp this concept.Take a candle you see light and walk away from the candle The light appears smaller and smaller has you move away to :mrgreen: you cannot see it at all.

The light does not get weak or despair it is just out side of your viewpoint. How can I understand this better and they go on that radio waves are like this too.

The stronger the candle or flash light the more light you will see or having a better eyeglasses will allow you to see the candle or flash light better.Than they go on saying radio waves are like this the more trasmitting power the more you will pick up or better the antenna the more you will picks up.

Then say the key is good antenna.The big dish antenna NASA uses take all the energy and concentrate the energy to center point.But does not really explain how it works.

I'm also trying to understand how NASA can pick up radio signals millions of light years away .

I'm not sure what question you are asking. Why does a radio signal get weaker as you get further away ? Think about your candle. It gets smaller but it also gets dimmer. This is why you can't see it eventually, it's because it got too dim not too small. Think about seeing stars at night. The stars are very far away and as (apparently) small as they can get. Yet, if the star is bright enough, you can still see it.

Now as for antennae ... are you asking why a big antenna can receive a weak signal or are you asking how an anenna works ?

 

[DrRocket]

Okay first I'm trying to grasp this concept.Take a candle you see light and walk away from the candle The light appears smaller and smaller has you move away to :mrgreen: you cannot see it at all.

The light does not get weak or despair it is just out side of your viewpoint. How can I understand this better and they go on that radio waves are like this too.


The stronger the candle or flash light the more light you will see or having a better eyeglasses will allow you to see the candle or flash light better.Than they go on saying radio waves are like this the more trasmitting power the more you will pick up or better the antenna the more you will picks up.

Then say the key is good antenna.The big dish antenna NASA uses take all the energy and concentrate the energy to center point.But does not really explain how it works.

I'm also trying to understand how NASA can pick up radio signals millions of light years away .

The reason that light and radio waves (both are electromagnetic waves or more correctly photons) get weaker with distance is simply due to geometry. Think of a point source (all sources from great distances are adequately approximated by point sources) which radiates uniformly. The intensity at a distanc point on the surface of a sphere is simply determined by the fraction of the surface of that sphere covered by the receiving apparatus. The areas of a sphere is pi*r^2 where r is the radius. So it follows from just this simple formula that the far field strength of an electromagnetic field drops off proportionally to the square of the distance from the source.

When you use a lens that lens concentrates the receiving signal from an area determined by the radius of the lens to a smaller area, the image formed, that is determined by the focal length of the lens. The same argument applies to an antenna. That is why one can use receiving equipment to concentrate an incoming signal and to detect signals that are not detectable by the nakes eye, or by receivers with small antennae.

 

[nec208]

I'm asking why a big antenna can receive a weak signal .

about your candle. It gets smaller but it also gets dimmer. This is why you can't see it eventually, it's because it got too dim not too small. Think about seeing stars at night. The stars are very far away and as (apparently) small as they can get. Yet, if the star is bright enough, you can still see it

I understand the effect just do not know why it is like that.

 

[Mee_n_Mac]

I'm asking why a big antenna can receive a weak signal .

about your candle. It gets smaller but it also gets dimmer. This is why you can't see it eventually, it's because it got too dim not too small. Think about seeing stars at night. The stars are very far away and as (apparently) small as they can get. Yet, if the star is bright enough, you can still see it

I understand the effect just do not know why it is like that.

OK, I think I can use a simple analogy that will explain how this works. Think about a rainstorm. In this special rainstorm it rains just as hard (the same number of raindrops per second) on every square foot over the entire area where it rains. Now which do you think will collect more rain in any 1 second interval, a round bucket with a mouth that is 1 ft in diameter or a round bucket with a mouth 10 ft in diameter ? Obviously the bigger mouth bucket collects more rain and this is true no matter if it's a moonsoon or barely raining at all. In this analogy the rain is like photons of light or radio energy. A lot of raindrops per second is a strong signal, a few drops/sec is a weak signal. A large bucket is like a large antenna, it collects more raindrops than does a smaller one. So now let's set a level for the minimum detectable signal. Any signal weaker than this won't get noticed*. Let's pretend it's 10 drops/sec. When it's raining very hard, say 1000 drops/sec over each square foot, a small "bucket" will collect the needed 10 drops in 1 second. However when it's raining very lightly, say 1 drop/sec for each square foot, you can see you need a bucket whose mouth is 10 square feet in size to get the minimum detecable signal. And that's why for very weak radio signals you need a large antenna. It's a big "bucket" to catch the few photons/sec that are falling on it.

Your second question has to do with how radio waves spread out as they travel. Again we can use the analogy of water drops to help you imagine the answer. Let's squirt water out of a hose. It spreads out the further from the hose the water travels. If we wanted to collect all the water and not miss a drop we could use a relatively small bucket 1 foot from the hose end. If we're going to be 10 ft from the end, we'll need a bigger bucket to collect every drop. If all we have is a "small" bucket then we're going to miss some of the water. Now imagine we have the small bucket and we're even further away. With this setup we might collect only a drop or 2 every second. In each of the 2 cases we're collecting a weaker flow of water. The signal we receive it getting weaker/dimmer because it's spreads out and we only have a certain size bucket to collect it. With a bigger bucket the signal wouldn't be as dim which is why you can see dim stars with a telescope and not with your eyes alone.

*If it helps you can think of the bucket as having a leak that looses 9 drops/sec. You check every second and if there's a drop left you can see it. That's why you need 10 drops/sec for a detecable signal. This last part is further from the actual truth of how radio reception works but it'll do for now.

 

[docm]

Wiki's article on the Inverse Square Law;

http://en.wikipedia.org/wiki/Inverse_square_law

First: there is no difference between light, radio waves, x-rays etc. etc. They're all electromagnetic radiation with the differences being those of wavelength. As such the ISL applies to all of them equally.

Let's use the example of a star whose light is emitted spherically. Take any conical section (actually a frustrum of the cone, with the narrow end being the stars diameter) out of that sphere and you'll see that its surface area gets larger as the "light" gets further from the source. This causes its total energy to be spread over an increasingly larger surface area, lessening its intensity at any fixed-size location along that path (your eye's iris, for example). This is why the light appears 'dimmer'- less and less of it is entering your eye as distance increases.

The apparent shrinking of the source is caused by a similar geometry in reverse: its image takes up a smaller and smaller angular portion of your field of view as distance increases.