# Tagged Questions

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### What are the limitations on the Paraxial Approximation?

What my physics book referred to as the paraxial approximation derived to be thus: $$\frac{1}{s}+\frac{1}{s'}=\frac{2}{R}$$ as a way of showing that in a concave spherical mirror, all reflected rays ...
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### What makes some materials more reflective that others? (atomic level)

I am an A-Level student doing some research into beryllium. I have found it is highly reflective due to its free electrons re-emmitting EM waves. One thing i am stuck on however, is why beryllium is ...
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### What happens to Newton's Third Law during the reflection of a pulse from a free end?

Well, it is known that a pulse gets inverted when it gets reflected from a fixed support while the polarity of the pulse remains same when the incident pulse gets reflected from a free end. However, ...
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### statistical property of light reflected from a coarse mirror

This is a problem comes up in my study in correlation reflectometry. I'm wondering if there is a straight-forward way to interpret the phase and amplitude of the reflected light from a perturbed ...
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### What happens when light is reflected from a surface moving in a medium with a huge refractive index?

Imagine a mirror is moving away from a light source in a substance through which the speed of light is very slow -- so slow that the speed of the mirror is close to being the same as the speed of the ...
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### Bragg reflected electrons

Could you explain how does bragg reflection happen for electrons? What does it mean that when they satisfy Laue condition? This already is asked in Physics SE. They are Bragg reflected in the opposite ...
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### Modeling a spray painted polyurethane surface reflection

I'm modeling light interaction/reflection from a fiberglass surface with polyurethane epoxy (that is very reflective) that has been spray painted with a matte black paint. I'm looking for some input -...
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### Time involved in reflection

Consider light bouncing back and forth between two ideal front surfaced mirrors. How long does the process of reflection (i.e., absorption and re-emission) take?
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### Constructing a chriped dielectric mirror for negative dispersion for ultrashort laser pulses resulting in group velocity delays

I'm currently looking at designing a chirped mirror for a project but I am confused over several aspects. I understand the principle of a chirped mirror in terms of how a laser pulse has a broad set ...
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### Why do different color materal differ temperature in the same sunlight?

I have a blue, red, and green cup and put a thermometer in each. Of the 3 the blue cup had the coldest temperature inside, then green, then red. I understand there may be differences in the ...
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### Standing Waves in a String of two Linear Densities

Given a string with sections of two linear densities like this: Does the point where the two linear densities meet have to be a node if a standing wave is produced? Are there alternatives? Could I ...
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### How do Hertzian dipoles relate to reflection of EM waves?

We recently performed an experiment where the intensity of microwave radiation reflected off different materials was measured. A comment in the script noted that the mechanism by which reflection of ...
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### What happened to the perfect mirror?

Back in 1998 an article was published in Science by JPL's Jon Dowling claiming a method for making a perfect dielectric mirror: "Mirror on the Wall: You're Omnidirectional After All?" Jonathan P. ...