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Optics: Real vs Virtual Images

by Gale
Tags: images, optics, real, virtual
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Gale
#1
Sep28-07, 05:06 PM
P: 676
Hi,

So, I'm confused about the difference between real and virtual images. Lets use a concave mirror for example. I understand that a real image is formed when the actual light rays reflect off the surface and converge to one point. A virtual image is formed when the rays don't themselves converge, but if you continue you them through the mirror they converge on the other side. So, its said that the real image could be seen on a screen, whereas the virtual could not. So, do I see the virtual image in the mirror? Can I see the real image without a screen? Can one mirror produce both types of images? I can get the answers when I do the problems, but I'm just not clear what it means.

Could someone help clarify?
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Doc Al
#2
Sep28-07, 05:28 PM
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Quote Quote by Gale View Post
So, its said that the real image could be seen on a screen, whereas the virtual could not. So, do I see the virtual image in the mirror?
Yes. Just like when you look at yourself in the bathroom mirror, you are looking at a virtual image that appears to be inside the mirror.

Can I see the real image without a screen?
Sure, depending on where you are. It will look like it's suspended in air. There's a cool toy called "the mirage" that produces a real image in the air. Check out the video: The Mirage Optical Illusion
Can one mirror produce both types of images?
A concave mirror can produce a real or virtual image, depending on how close the object is. A convex mirror will always produce a virtual image of an ordinary object.

This site might help: Ray diagrams for mirrors
Gale
#3
Sep28-07, 05:49 PM
P: 676
I guess I get most confused when I think of a flat mirror. I feel like the image I see is virtual, because it appears in the mirror, right? But aren't all the rays parallel? I also feel like if I held up a screen I should be able to get a real image reflected from the mirror. Also, if I had a lazer pointer and shined it at any mirror, I feel like I would get a real image, since I think I could hold a screen at some point and have the lazer light fall on it. I feel like I just don't have a solid grasp of the real life effects of a real or virtual image. I feel confused.

I tried playing with a spoon the other day, (concave or convex mirror depending on how you hold it) and a compact mirror and I was just struggling to distinguish what's what. The diagrams make sense, since I can tell you based on the math and diagram if its a real or virtual image, and where it will be and right side up or whatnot. But if I'm just handed a mirror and try to intuitively understand, I get lost.

Doc Al
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Sep28-07, 06:20 PM
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Optics: Real vs Virtual Images

Quote Quote by Gale View Post
I guess I get most confused when I think of a flat mirror. I feel like the image I see is virtual, because it appears in the mirror, right?
Right.
But aren't all the rays parallel?
No. Each point on the object sends out light in all directions. See this: Image Formation in Plane Mirrors (View the animation.)

I also feel like if I held up a screen I should be able to get a real image reflected from the mirror.
Try it and see.
Also, if I had a lazer pointer and shined it at any mirror, I feel like I would get a real image, since I think I could hold a screen at some point and have the lazer light fall on it.
Not sure what you mean. You can certainly use a mirror to deflect the laser beam. But not sure what that has to do with images of ordinary objects.
I feel like I just don't have a solid grasp of the real life effects of a real or virtual image. I feel confused.
Don't give up. It takes time to build up a physical intuition. (It's not uncommon to be able to "solve" problems before you really understand the material. That's how you learn.)
Ryker
#5
Aug23-10, 12:21 PM
P: 1,088
Since this is tangentially related to this topic, which I found through google - that's why I'm resurrecting it and not making a new one - I had a question similar to the ones OP already set. Revising my knowledge on mirrors, I was looking at a spoon today, but could only get a real upside down image of my giant head. Is this due to the fact that I can't get past the focus point and still be able to see the image?
jtbell
#6
Aug23-10, 02:31 PM
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Yes. If you get very very close to the spoon (I'm assuming you're looking at the concave side), you can probably get a virtual image, but it will only show your eye. If you can see your eyebrows in the image, that will tell you whether it's upright (virtual) or inverted (real).
Ryker
#7
Aug23-10, 03:27 PM
P: 1,088
Thanks for the answer, I figured this would be the case, but just wanted to make sure.


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