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Thread: Why I can burn a paper with magnifying glass and sun?

  1. #1 Why I can burn a paper with magnifying glass and sun? 
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    Why I can burn a paper with magnifying glass and sun? Isn't it something to do with the electromagnetic field (because light is itself electromagnetic field)?


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    It simply focusses the light that falls over the area of the magnifying glass all into one spot.


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    It is called refraction, and yes it has to do with the electromagnetic field. The light wave changes direction due to the difference in the speed of light in the two refractive media.
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    Quote Originally Posted by Harold14370
    It is called refraction, and yes it has to do with the electromagnetic field. The light wave changes direction due to the difference in the speed of light in the two refractive media.
    And what happens in the paper? Do the electrons react opposite to the electromagnetic field?
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    Basically burning is just giving the atoms enough energy to change their state (by state mean changing into another substence) and in this case combine with oxygen/oxidise or in effect ''burn''.
    What you are doing is giving the area of paper light (a form of energy) and concentrating it so that the paper atoms now become higher energy and can burn in the air.

    All it is, is giving energy.

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    Quote Originally Posted by Barry Flannery
    Basically burning is just giving the atoms enough energy to change their state (by state mean changing into another substence) and in this case combine with oxygen/oxidise or in effect ''burn''.
    What you are doing is giving the area of paper light (a form of energy) and concentrating it so that the paper atoms now become higher energy and can burn in the air.

    All it is, is giving energy.

    Barry
    Why then, if I put just magnet, I will not burn the paper? It is again energy.
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  8. #7 Re: Why I can burn a paper with magnifying glass and sun? 
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    Quote Originally Posted by scientist91
    Why I can burn a paper with magnifying glass and sun? Isn't it something to do with the electromagnetic field (because light is itself electromagnetic field)?
    You are merely concentrating the sun's rays to a smaller area. THis energy knocks electrons out of orbit and therefore breaks the ionic/chemical bonds of the various elements. all these ions then look around for something to share their shells with and find oxygen molecules the easist to bond with, forming CO2 etc - that's all from a long time (and many beers) ago, so any of you youngsters out there feel free to correct me if I'm wrong.
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  9. #8 Re: Why I can burn a paper with magnifying glass and sun? 
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    Quote Originally Posted by Megabrain
    Quote Originally Posted by scientist91
    Why I can burn a paper with magnifying glass and sun? Isn't it something to do with the electromagnetic field (because light is itself electromagnetic field)?
    You are merely concentrating the sun's rays to a smaller area. THis energy knocks electrons out of orbit and therefore breaks the ionic/chemical bonds of the various elements. all these ions then look around for something to share their shells with and find oxygen molecules the easist to bond with, forming CO2 etc - that's all from a long time (and many beers) ago, so any of you youngsters out there feel free to correct me if I'm wrong.
    But isn't the light electromagnetic field? Again I put magnetic field with the magnet? What is the difference?
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    Guys, try to tell him that this effect has nothing to do with electromagnetic fields, or the fact that that light is an electromagnetic wave.

    Recall that sound can also be focused, for example by a CO2 convex lens. Focusing is simply a property of a wave, any kind of a wave. Electromagnetic properties are irrelevant and misleading.

    So is any explanation of burning in terms of electrons. Paper gets hot enough, it bursts into flame! Invoking electrons is totally misleading here; the kid will think that electromagnetic theory is somehow involved.

    Everyone should try to tell him so. He has a tendency not to listen.
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    Quote Originally Posted by SteveF
    Guys, try to tell him that this effect has nothing to do with electromagnetic fields, or the fact that that light is an electromagnetic wave.

    Recall that sound can also be focused, for example by a CO2 convex lens. Focusing is simply a property of a wave, any kind of a wave. Electromagnetic properties are irrelevant and misleading.

    So is any explanation of burning in terms of electrons. Paper gets hot enough, it bursts into flame! Invoking electrons is totally misleading here; the kid will think that electromagnetic theory is somehow involved.

    Everyone should try to tell him so. He has a tendency not to listen.
    I have tendency to not to listen? OMG, when I don't understand something, I try to understand it, ok? First, what is happening in the microstructure of the paper? There must happen something with the structure which will make paper burn.
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  12. #11  
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    It is called refraction, and yes it has to do with the electromagnetic field. The light wave changes direction due to the difference in the speed of light in the two refractive media.
    he is right scientist91 but where your missing the point is that its the electromagnetic wave causing focusing which is causing the change in the energy. It is not directly the field itself. thats why magnets don't burn paper.

    I forget which famous scientist discovered this but if you find his work you will get it better. He found that light takes the easiest path through whatever substance its traveling through thats why things kind of loose their shape under water and what not. I think its called snell's law.

    http://en.wikipedia.org/wiki/Snell%27s_law
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    i got another question, is it the amplitude, or the wavelength that changes when you focus the light with a lens?

    AFAIK, light = waves = energy = heat.
    more energy = more heat.
    since the light is focused by the lens, does that mean other parts of the paper becomes less heated?
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    i got another question, is it the amplitude, or the wavelength that changes when you focus the light with a lens?
    None of the above. You simply pack more rays into a small area. A light meter would register greater intensity of light, but this is not quite the same as saying there is greater amplitude. (If anyone disagrees, he might actually be more correct than I.)

    since the light is focused by the lens, does that mean other parts of the paper becomes less heated?
    Yes.
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    Remember this? All you are doing is providing heat (energy) by focusing the light rays, (photons) whatever. There needs to be fuel as well, or more accuratley, a peramanent catalyst to which will react with. You could try oscillating the light rays by moving the magnifying glass closer so that less photons get caught in the air above the paper, increasing the energy moreso.
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    There needs to be fuel as well, or more accuratley, a peramanent catalyst to which will react with.
    Ok, obviously the paper is the fuel. As far as a catalysts are concerned, it is a runaway reaction. The initial flame heats the paper to its sides to a point where it combusts (carbon, I think, combining with oxygen in this case) and this in turn heats the paper to it's sides untill the paper is burned out.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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    When paper is in normal sunlight, it will not burn.

    All that you are doing is focusing is the sunlight onto specific smaller areas of the paper than the Sun's normal rays would. You are increasing the intensity of light in some areas, and decreasing it in others.

    Notice how when you put the magnifying glass over the paper, the center is very bright, and there is a thick dark circle surrounding it. The dark circle is just the magnifying glass causing less light waves to go there -- like a shadow. The bright center dot is the magnifying glass causing more light waves to go there. This is the area with the most intense sunlight, sun rays, photons whatever you want to call them. They are simply an energy source which will then cause the paper to combust, as in burn.

    The main thing is that you need more photon intensity than normal sunlight (unfocused) to reach the threshold required to burn the paper.
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  18. #17 Waves 
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    Imagine getting a square bowl of water and dropping a stone in it.

    The waves will spread outwards uniformally. Now place two dvd cases standing on their sides touching one of the sides of the bowl, but place them so the angle is kind of like a triangle.

    now drop the same stone, and again the waves will spread out uniformally, but will then hit the sides of the dvd cases and as the angle gets narrower and narrower, the more focused the wave becomes.

    Notice, the wave length doesnt change, nor does the frequency but the energy DOES. It will hit the point of impact on the wall with more energy because it has been focused.

    (This is just my thought esperiment, so feel free to correct me if im wrong)
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  19. #18  
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    But what happens with the atoms and molecules in the magnifying glass? Why we receive zoomed picture?
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    the light is focused by the simple process of refraction. imagine two wheels connected by an axle. I push the wheels in the center of the axle. They are at first rolling on concrete. There is a rug on the concrete though. if the wheels hit that rug at differant times (because they are roling at... say a 30% angle to the carpet) the first wheel to hit the carpet, will slow down, while the other wheel will keep the same speed until it hits the carpet. when they hit the carpet, the wheel speeds will match. The little thing is now traveling at a differant angle.

    Now immagine that the carpet is a circle, or is shaped like a magnifying glass from the sideways view. shoot 5 little sets of wheels straight at it. they will change directions in a way that all of them will hit one central point. That point is where all of the energy is concentrated.
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  21. #20  
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    And how I can determine, how zoomed I'll see the image when see through magnifying glass? Why X is like on the picture?
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