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# Optics: No.of images formed? watch

1. If you are standing in a room whose 2 adjacent sides and the top ceiling is mirror, how many images of yours will be formed?

Thanks
2. Is this a trick question?
3. What's a bottom ceiling?
4. (Original post by TableChair)
What's a bottom ceiling?
Ok, its just ceiling, not top or bottom.
5. 6 virtual images
6. (Original post by teachercol)
6 virtual images
Can you please explain it to me?

Thanks
7. (Original post by teachercol)
6 virtual images
Once you go beyond the first 3 virtual images due to the initial reflections in the 3 mirrors, the next reflection produces a virtual image of each of those 3 virtual images in the other two mirrors. (=6 more images) Each of those produces 2 images in the other two mirrors. (=12 more). And so on...
So the number of images produced is 3 + 6 + 12 + ....
The number is theoretically infinite, but in practice of course there are a number of factors which would limit this; absorption of the light being one.
8. (Original post by Stonebridge)
Once you go beyond the first 3 virtual images due to the initial reflections in the 3 mirrors, the next reflection produces a virtual image of each of those 3 virtual images in the other two mirrors. (=6 more images) Each of those produces 2 images in the other two mirrors. (=12 more). And so on...
So the number of images produced is 3 + 6 + 12 + ....
The number is theoretically infinite, but in practice of course there are a number of factors which would limit this; absorption of the light being one.
Actually, I've changed my mind on that, my brain hurts.
I think it's 3 + 6 + 8 + 10 etc for each subsequent reflection.
9. So, theoratically the answer will be infinite?

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10. So, theoratically the answer will be infinite?
I think you get a finite number of reflections in the situation you describe, even in theory, even with perfectly reflective mirrors (i.e. no energy loss in reflection). I think this because any light beam reflecting perfectly perpendicular to the mirror will have originated from you, meaning it will reflect back into you and be absorbed. Think about it - if you stare straight into a mirror with another behind you, all you see is yourself once - not an infinite number of reflections.

At an angle slightly off the perpendicular, the path of the beam is such that it will eventually reflect off the surface of one mirror and miss the other, leading to it being absorbed by one of the two non-reflective walls.

Had you said a cube whose interior was comprised of perfect mirrors, i'd me more inclined to believe that infinite reflections could be possible, but even then im not sure without more thought...

Those are my thoughts on this!
11. (Original post by utsav55)
So, theoratically the answer will be infinite?

Thanks
It depends how far you want to push the word "theoretically".
In practice there could be a large number of multiple reflections. The number you see would depend on the factors I and s_l_n_h mentioned in post 10. Particularly, how near to parallel the opposite mirrors are, and how near they are to 90 deg to the other mirror.
My definition of "theoretically" was purely mathematical. That is, I assume that an image is always produced an equal distance behind the mirrors, irrespective of whether the you, the object, are able to see it. After all, it could be observed by a different observer standing nearby.

There are 3 initial definite images of you, one in each mirror; after that there are as many images as you want depending who you ask and how far you want to push the multiple reflection question.
12. Could this be related to corner cubes?
13. (Original post by Stonebridge)
It depends how far you want to push the word "theoretically".
In practice there could be a large number of multiple reflections. The number you see would depend on the factors I and s_l_n_h mentioned in post 10. Particularly, how near to parallel the opposite mirrors are, and how near they are to 90 deg to the other mirror.
My definition of "theoretically" was purely mathematical. That is, I assume that an image is always produced an equal distance behind the mirrors, irrespective of whether the you, the object, are able to see it. After all, it could be observed by a different observer standing nearby.

There are 3 initial definite images of you, one in each mirror; after that there are as many images as you want depending who you ask and how far you want to push the multiple reflection question.
Actually yes, a numerical answer like 3, 6 or infinite etc.

The question is just as in my first post, no other detail or description is in the question.

Thanks
14. I would hope (and suspect) your teacher is testing you on your knowledge of reflection and images in a plane mirror. I also suspect he/she is prepared to accept any carefully reasoned answer based on good physics. Have you drawn ray diagrams for plane mirrors?
If you do this with the 3 mirrors looking like 3 sides of a rectangle, and the object in the middle, you could draw in the 3 first images, one in each mirror, an equal distance behind the mirror as the object is in front.
It then gets tricky if you want to draw the multiple reflections. The first set of these you get by placing images of those 1st 3 images. You should be able to find 6 of these, one behind each wall, further away than the 1st image, and 2 in each "corner". They actually superimpose on each other if the mirrors are at exactly 90 deg.
Good luck.
15. (Original post by Scipio90)
Could this be related to corner cubes?
Yes, you would get a similar effect in the corners where the wall joins the ceiling so long the angle is at 90 deg.

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