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nonequilibrium
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So I'm using Serway, not the thing you should expect a lot of insight from, but I do try.
Anyway, I know how convergent lenses work. So here is the following usual case:
[PLAIN]http://www1.union.edu/newmanj/lasers/Geometrical_Optics/ConvLensCase2.gif
You see the convergent lens creates a bigger thing to look at. On the other hand, the bigger thing is also farther away. I just assumed the being-bigger part weighed up to the being-farther-away part. But now my book has come to "The Simple Magnifier" and states "The size of the image formed at the retina depends on the angle theta subtended by the object at the eye."
Does it just postulate this? Is it evident? Okay, it does sound very intuïtive. But anyway, the book goes on to say that we can't see things closer than about 25cm (I'm sorry if you use other units, but you know what I'm talking about: the near point). It then suggests that we use magnifying glasses so we can put objects closer than 25 cm, cause the magnifier will create a virtual image that is farther away than 25 cm (but larger) which is visable. So basically, they say, a magnifying class is not useful for making an angle larger, it's actually there to make larger angles possible (because it then says, if your eye were RIGHT behind the lens, the smaller object and the larger image form the same angle (from their peaks to your eye), it's just that you can't see the small object, but you can see the larger image[note: ignore the colored lines on the image, they're meaningless for my discussion]).
This seems very weird. I can take a magnifying glas and hold it half a meter away from me, hovering 10 cm above some map and I see the letters on the map in bigger letters. But following the book's logic, it shouldn't make a difference, because I can actually see the map because it's far enough. (of course the book doesn't actually state this, but it does seem to follow out of their reasoning, doesn't it?) Or does a magnifying glas simply have two distinct uses:
1) make more angles possible when an object is too close
2) make objects look bigger. (<-- this one does sound subtle, is it bigger in this case because my eye is far from the magnifying glas and so the angle of the virtual image is way bigger than that from the actual letters on the map?)
I'm a bit confused... I hope somebody else gets my confusion.
Thank you,
mr. vodka
Anyway, I know how convergent lenses work. So here is the following usual case:
[PLAIN]http://www1.union.edu/newmanj/lasers/Geometrical_Optics/ConvLensCase2.gif
You see the convergent lens creates a bigger thing to look at. On the other hand, the bigger thing is also farther away. I just assumed the being-bigger part weighed up to the being-farther-away part. But now my book has come to "The Simple Magnifier" and states "The size of the image formed at the retina depends on the angle theta subtended by the object at the eye."
Does it just postulate this? Is it evident? Okay, it does sound very intuïtive. But anyway, the book goes on to say that we can't see things closer than about 25cm (I'm sorry if you use other units, but you know what I'm talking about: the near point). It then suggests that we use magnifying glasses so we can put objects closer than 25 cm, cause the magnifier will create a virtual image that is farther away than 25 cm (but larger) which is visable. So basically, they say, a magnifying class is not useful for making an angle larger, it's actually there to make larger angles possible (because it then says, if your eye were RIGHT behind the lens, the smaller object and the larger image form the same angle (from their peaks to your eye), it's just that you can't see the small object, but you can see the larger image[note: ignore the colored lines on the image, they're meaningless for my discussion]).
This seems very weird. I can take a magnifying glas and hold it half a meter away from me, hovering 10 cm above some map and I see the letters on the map in bigger letters. But following the book's logic, it shouldn't make a difference, because I can actually see the map because it's far enough. (of course the book doesn't actually state this, but it does seem to follow out of their reasoning, doesn't it?) Or does a magnifying glas simply have two distinct uses:
1) make more angles possible when an object is too close
2) make objects look bigger. (<-- this one does sound subtle, is it bigger in this case because my eye is far from the magnifying glas and so the angle of the virtual image is way bigger than that from the actual letters on the map?)
I'm a bit confused... I hope somebody else gets my confusion.
Thank you,
mr. vodka
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