Optics question: Looking at mirrors from parallel to the surface

  • #1
Grasshopper
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I did a little experiment recently where I took a plane mirror and held it underneath a ceiling light. Then, I began to lower my head so that my view was closer and closer to the surface. When I did this, the image of the light began to drift lower and lower in the mirror until it completely disappeared.

I am curious about what would happen if I repeated the experiment using a convex mirror (by this I mean curved TOWARD the ceiling light). Because we can see the reflection of the sun on the ocean, I imagine that the image wouldn't fall below as much if I were to place my head near the surface of the mirror.

Unfortunately, most physics websites I've seen describe curved versus plane mirrors from the perspective of far away from the surface of the mirror. They'll usually only focus on light coming perpendicular from the object and how that reflects on the mirror.

So can anyone help me find some good diagrams about what these types of mirrors look like according to a viewer near the surface? Any contributions you can give are appreciated.
 

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  • #2
anorlunda
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Was the mirror silvered on the front of the glass or the back of the glass?
 
  • #3
Grasshopper
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Was the mirror silvered on the front of the glass or the back of the glass?
It’s hard to tell, but I THINK it’s silvered on the front of the glass (the flat mirror I used; and again, when my eyes were further away from the mirror, I could see the ceiling light, but when my face was right at the surface, the reflection was well below what I could see).
 
  • #4
A.T.
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I am curious about what would happen if I repeated the experiment using a convex mirror (by this I mean curved TOWARD the ceiling light).
You can use a big spoon to test that. Or a metal bowl.
 
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  • #5
tech99
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You may have seen an object floating on a still lake. This shows the inverted image, which touches the feet of the object without a gap. If the surface is curved in a convex manner, the image is smaller.
 
  • #6
sophiecentaur
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Was the mirror silvered on the front of the glass or the back of the glass?

It’s hard to tell, but I THINK it’s silvered on the front of the glass (the flat mirror I used; and again, when my eyes were further away from the mirror, I could see the ceiling light, but when my face was right at the surface, the reflection was well below what I could see).
It's unusual to find a normal domestic mirror that's silvered on the surface. Surface silvering is very easily damaged. Some stainless steel mirrors are used where ruggedness is needed. Or was this 'lab equipment'?
If there is a surface layer of glass (say 6mm thick) then you could expect some refraction effects when the paths are well away from the Normal (very oblique). Also, for very oblique incidence, you could be seeing images from multiple reflections from the two glass faces. That can seriously distort what you see if you are looking at a small bright object. (A laser pointer will show these up well).

We'd really need some sort of a diagram of your setup or we could have a different picture in our heads. If you google search for ray diagram mirror reflection ( or some variation on that) and select Images, you will see many different hits. You could copy a suitable image - that suits your question best.
 
  • #7
Keith_McClary
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If there is a surface layer of glass (say 6mm thick) then you could expect some refraction effects when the paths are well away from the Normal (very oblique).
Just touch a pencil to it and see the gap to the reflection. If it is not very clean you can see the reflection of every speck of toothpaste, or whatever.
 
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