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Physicsissuef
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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)?
Physicsissuef said:Ok, thanks. But what happens in the paper? Do the electrons react opposite to the electromagnetic field, which is concentrated in small area of the paper?
I am asking, is it exiting the electrons, so they release the excess of energy in form of heat and burn the paper?pixel01 said:The paper part in the focal area is heated by radiation so intensively that its temperature is higher than the burning temp of paper. It burns naturally. You put a piece of paper against a hot iron bar, it burns as well.
Physicsissuef said:I am asking, is it exiting the electrons, so they release the excess of energy in form of heat and burn the paper?
Physicsissuef said:I am asking, is it exiting the electrons, so they release the excess of energy in form of heat and burn the paper?
Physicsissuef said:Will I get the same effect if I get magnet, it have again energy?
rohanprabhu said:depends on how you use the magnet? Just moving the magnet over paper or something like that will do nothing [other than whatever friction will cause], because the paper is magnetically neutral i.e. it is non-magnetic. I can't really think of a way of how you can use it to directly radiate energy to the paper [u can like setup a small generator and stuff from the magnet.. but that'd be plain silly..]
also.. please be clear about your questions. It is incomprehensible in many instances..
Yah you know what? We try not to encourage dangerous experiments around here. :uhh:capnahab said:It is called the "kindling point". Next time aim (focus) the magnifing glass on the palm of your hand while trying to incinerate the unfortunate bug.
Yes. For example, if you build an electric motor for class, make sure you make the axle from something that is more heat resistant than a ballpoint pen. Trust me on this one.nanoWatt said:If you pass that magenet through a coil of wires you can generate heat through induction. Some induction systems are hot enough to melt minerals.
Absolutely nothing. The light passes right through them. More accurately, the bonds between the atoms do not absorb any of the passing photons that have frequenices in the visible light range. Thus, the photons continue straight on their merry path. They only change course at the interface between air and glass (and vice versa).Physicsissuef said:Do you know what happens with the atoms and molecules?
That's why I see zoomed picture? Because of the concentration of energy? By molecules and atoms a thought, what is the structure of the magnifying glass?Mephisto said:I don't think the OP's question of what goes on molecular scale was really answered. Concentrating the light means much higher intensity, therefore you have many many photons hitting small amount of material. How exactly, on a molecular scale does that translate into increased kinetic energy? (heat)?
I'm guessing the electrons in atoms that make up the paper respond to the EM pulse that is a photon, and gain kinetic energy through this interaction... Not exactly sure how it happens though
Physicsissuef said:That's why I see zoomed picture? Because of the concentration of energy? By molecules and atoms a thought, what is the structure of the magnifying glass?
Like http://laser.physics.sunysb.edu/~jennifer/pictures/refraction.gif"DaveC426913 said:No. We've got to separate out two questions here, just for clarity.
1] How does a magnifying glass burn things
2] How does a magnifing glass enlarge images
it's the same phenomenon but trying to combine the two in one answer will get confusing.
The magnifying glass enlarges things by bending the light rays from object to observer.
Light rays emanating from an object - say, a tiny dot of a flea - extend out in all directions. These rays diverge.
A magnifying glass placed close to the flea will intersect an angle of these diverging rays (let's say the angle is 20 degrees) and refract (bend) them so that all those rays are now converging and entering your eye.
Now think about what you'll actually see: you'll see an image of a flea that fills a 20 degree angle of your vision. That's got to be one big flea!
As for how the magnifing glass does its thing:
The internal structure of the magnifying glass has no effect on the light rays. The only thing that has an effect is the boundary between air and glass, and between glass and air. The only two factors that affect the light rays are: 1] the difference in optical density between the two media and 2] the angle of incidence of the rays to the boundary.
It is exactly what happens when you look into a pool or out of a pool and see a bent image. You can experiment with this easily by filling a drinking glass with water and sticking a straw in it. Watch how the boundary between air and water bends the light rays. The internal nature of the two media (glass or air or water) has no effect.
wiki: 'magnification', 'refraction', 'angle of incidence', 'optical density'
Physicsissuef said:Like http://laser.physics.sunysb.edu/~jennifer/pictures/refraction.gif"
HallsofIvy said:"Infra-red" light has frequency slightly less than visual light and caries more energy. It can excite other electrons than just those in our retina and cause feelings of warmth and heat. If it is strong enough, it can cause the electrons to move much faster, developing enough "friction" to cause fire.
DaveC426913 said:Yep.
Physicsissuef said:Ok, I understand now for magnification. Now, why pure glass does not concentrate energy like magnifying glass?
Yes, as rohanprabhu points out, "pure glass" will do the exact same thing. There is nothing special about the glass that a magnifying glass is made of. It is all about the shape.Physicsissuef said:Ok, I understand now for magnification. Now, why pure glass does not concentrate energy like magnifying glass?
That's what burning is. This is a different discussion.Ulysees said:Sorry to interrupt you here, but if the chemical reaction of combustion is occurring only at the paper, then why is light coming from the entire flame, which may be several cm long?
Ulysees said:Sorry to interrupt you here, but if the chemical reaction of combustion is occurring only at the paper, then why is light coming from the entire flame, which may be several cm long?
It follows it's not just the paper that's burning, also gases emitted from it when heated are burning. What gases would paper emit when heated?