# Tagged Questions

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### What happens to the index of refraction of a lens if placed in water?

What happens to the index of refraction and focal length of a lens that is initially in air that is then placed in water?
819 views

### Glass that only allows light of specific amplitude to pass through it

Is there a type of glass, mirror or lens that allows only lights of amplitude equal to or greater than a fixed value to pass/reflect through them?
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### Determining a person's sight from his speech [closed]

Suppose we meet a person wearing glasses.Can we determine whether the person is short-sighted or long-sighted? However,due to courtesy,we are not allowed to ask him to try the glasses and in general ...
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### Question about the refraction of Fresnel lenses

If you line up the suns rays parallel to a Fresnel lens, the light is concentrated, and the focus directly underneath. However, what happens if the sun is off to the side, making the light hit at an ...
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### How to calculate the heat of a metal?

Lets say I leave 100g of copper outside under a convex lens that is 1m squared in surface area (I've been told that 1m2 of sunlight equals 1Kw). How would I figure out the temperature reached for a ...
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### Spreading UV light? Fresnel lenses?

I'm making a little UV exposure box and I'm looking for a way to evenly spread out the UV light. I've used Fresnel lenses to do just this in the past, but that was for visible light. But from what ...
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### How to produce a loss-free combination of two “identical” beams?

This is for anyone with experience in optics/imaging/photography as well as anyone who likes to puzzle over tricky physics problems. As the title suggests, this is about combining two (for all ...
517 views

### Paraxial rays and marginal rays question

Paraxial rays are found to focus far away the lens whereas marginal rays focus near to the lens, why? I didn't find satisfactory answer in my academic book..
3k views

### Magnifying Glass-How does it work? [duplicate]

How does a magnifying glass work? I know it creates a virtual image of the observed object but how is it possible that humans can see the virtual image?
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### How does a lens affect the field of view in a mirror?

If one looks into a mirror, he can see a certain field of view. If he places a convex lens that magnifies (or a concave lens that does the opposite) in front of the mirror, but so that he can still ...