Explaining the Optical Illusion on a Spoon

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SUMMARY

The optical illusion observed on a spoon arises from the differing properties of its concave and convex surfaces. The concave side acts as a concave mirror, producing an inverted and real image when the object is beyond the focal point (F), while the convex side functions as a convex mirror, yielding a virtual, upright, and smaller image. When positioned close to the concave side, a magnified and upright image can be seen, similar to the effect of shaving mirrors. Understanding these principles relies on geometrical optics.

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wasia
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Hello!

I have a problem - a non-physics student has asked: "Why do I see my face upside down on one side of a spoon, while it is O.K. on the other side?"

How to explain it? The only method I thought of was geometrical optics. Is it possible to clarify this phenomenon without drawing?

Thanks a lot!
 
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One side of the spoon acts as a concave mirror (the side you scoop up with), the other acts as a convex mirror. In a concave mirror, if the object lies is at a distance greater than F from the mirror, where F is the focal dist, then the image formed is real and inverted. In a convex mirror, the image is always virtual and upright and smaller. The spoon has a very small F and that’s why you see an inverted image on the concave side, and an upright smaller image on the convex side.

If you take your face very close to the concave side of the spoon, than you will see an upright and magnified image. That’s how shaving mirrors work. In a spoon it may be difficult to see.
 
You could try drawing a simple ray diagram for both cases to aid the explanation.
 
Both answers include geometrical optics :(
 
Well so what? I think a person able to ask that question could understand a simple, ''the concave nature of the spoon acts as a mirror which flips an image at its focal point''. How deep of an answer is your friend looking for?
 
That is the correct answer!
 

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