# Tagged Questions

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0answers
21 views

### Is image scale the same as focal length?

I am supposed to show using a diagram how image scale is related to focal length. But my formula for image scale is $$\text{image scale} = \frac{y}{\theta} = F$$ where $y$ is the image size on the ...
1answer
93 views

### If I observe a planet because of reflected sun-light, how does the radiant flux vary with distance?

I wish to figure out how the flux of the sun's reflected light from a planet varies with distance, so assume an observer is on the sun, looking at a planet, and the light originating from the planet ...
0answers
50 views

### Why the underside of an object isn't a different colour after light reflects off a different coloured surface

If you were to place a blue plate in front of a green background and shine a light at the blue plate. The light that hits the blue plate would reflect the blue wavelength and when the reflected ...
0answers
47 views

### Help with finding an equation to work out the length of cable required to produce loss of colour on an analogue video signal

When I briefly taught Broadcast Engineering I set up an experiment in order to demonstrate the effect of signal reflections along coaxial cable on an analogue PAL waveform. It involved getting the ...
2answers
77 views

### Polarisation by Reflection - oscillation direction

I'm currently studying polarisation by reflection, and have come across two pieces of information from the same source, which I can't seem to understand on how they differ. The oscillation direction ...
3answers
3k views

### Is true black possible?

Black is the absence of light because it absorbs light, but when we create black paint or black objects, light is always reflected, either in all directions in matte or smoothly in shiny black objects,...
0answers
98 views

### 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 ...
1answer
153 views

### Minimum glare from reflected sunlight [closed]

I'm studying for the IB Physics HL exam, and I came across a question neither my physics teacher or I can solve. It has a diagram like so: The text of the question is this: A person wearing ...
1answer
140 views

### Can a one-way mirror effect be reversed?

I understand to get the effect of the one-way, one side needs to have light to produce the mirror, leaving the darkened side with the ability to see through. I would like to know if there is a way to ...
0answers
139 views

### hiding joint lines of plain mirrors

For some experiment I took two rectangular pieces of front surface mirrors, and joined it at 30 degree. However, the joint line is visible clearly, how do I hide it ? I guess I need to apply some ...
2answers
217 views

### Calculate required power output for a laser

How to calculate power rating required for a laser in order to produce a dot at a specific distance after reflection? For example, the laser is 10cm from the mirror, at an angel of 30 degrees it ...
1answer
72 views

### Optical system for cloning an image of a light source?

I need to create an optical system for cloning an image of a light source to human eyes. Is there a correct solution(design) for this problem. Reflectivity of the mirrors must be equal. Because ...
1answer
220 views

### Would we see the past if we look to a mirror 1 light year away? [duplicate]

What would we see if we place a mirror 1 light year away? Would we see the present or the past?
2answers
77 views

### How would a plane hitting a ball move (opposite of Pong)?

When a moving ball hits a stationary plane at an angle of incidence to the normal, it bounces away at the same angle (the angle of reflection), which is commonly understood. My question is 1) What ...
1answer
225 views

### Wave interference on window film coating

"The windows in an office tower are coated with a film to minimize reflected light of wavelength 550 nm. If the glass has an index of refraction of 1.52 and the film coating has an index of refraction ...
1answer
35 views

### Distinguishing between perfect rigid mirror and symmetrical universe

I have a relatively bizarre question which I'm not even fits into the category of mainstream physics, but here I go anyway. I want to consider two hypothetical situations. Then I want to see if there ...
0answers
24 views

### Phase change by reflection [duplicate]

Let's consider a light ray falling on a cuboid made of glass at the angle $\alpha$. Then there will be a reflected ray $A$. The ray will also refract. Let the refracted ray be $B$. Ray $B$ will be ...
1answer
154 views

### Reflection of Sound wave (Pressure Wave)

I want to study about the phenomenon of reflection of pressure waves as in an open ended organ pipe. Please suggest a suitable resource? I know about the harmonics in a stretched string and I can use ...
0answers
66 views

### What is the “Obscuration Factor (OBF)”?

In a paper I am reading for my master thesis I came across this "obscuration factor (OBF)". The authors indicate that it is a measurement of the average intensity of reflection. They do not give a ...
1answer
455 views

### Surfaces that reflect UV rays

I've been trying to research what surfaces reflect UV rays for the past day but it's been difficult coming up with definitive answers. So far what I've found is that surfaces that reflect visible ...
1answer
336 views

### What causes these rainbow effects using a polarizing filter on an airplane?

I know that light reflected from a surface at 45° is polarized and that for a similar reason skylight arriving from a direction orthogonal to the sun is polarized too. Photographers make use of this ...
0answers
120 views

### Would you be able to see yourself in a mirror in front of you as you two are in a room traveling at the speed of light? [duplicate]

Veritasium talked about this in one video. If you are in a room or a train, plane, car or whatever just a closed space traveling at the speed of light and you put a mirror in front of you, could you ...
1answer
323 views

### Metal Refractive index

I'm working on Fresnel equation for calculation of reflection of a light (532 nm) on Iron. I've got a question: Is metals refractive index always a real number or it can be a complex number?
2answers
187 views

### Why does the light instantly disappear when we switch off the source?

For example i take a box which is completely covered by the most perfect mirrors possible inside and inside that box i have a bulb whose bulb holder is also covered with the most perfect mirrors ...
0answers
49 views

### Model of scattering in wet things

You know that clothes and some surfaces become darker when wet (covered in an earlier question: why wet is dark?), because of the disordered reflections or of the refractive index of water or ...
1answer
40 views

### What is the phenomena where an object is repeated in a glass surface?

I don't understand why this happens. Is the image being repeated because the light is being bounced back and forth on the multifaceted surface?
2answers
415 views

### Probability current in scattering problems

This is a section from Wikipedia: In regions where a step potential or potential barrier occurs, the probability current is related to the transmission and reflection coefficients, respectively $T$...
1answer
137 views

### Light absorption for different liquid

when I was working on a cylindrical glassy bottle that filled with water, I found that the initial light intensity is less than the final light intensity. (It's clear but I experiment this) This is ...
1answer
85 views

### Why does light reflected on water tends to 'smear' in the vertical direction? [duplicate]

I have noticed that in city lights reflected on the water are very often smeared more in the vertical direction (relative to the reflecting plane I presume), than in the horizontal direction. See, for ...
1answer
61 views

### Can a virtual image created by a mirror have position in front of the mirror?

I dont think so, because then the rays will intersect and the image will be real. Please let me know if you know a case in which a virtual image is formed in front of the mirror.
1answer
142 views

### Can gravitational waves resonate?

Can gravitational waves resonate? - Perhaps by creating standing wave interference in a cavity? Could that feasibly happen either in nature or by engineering?
2answers
65 views

### Ideal mirror properties [duplicate]

Suppose there is sphere which is completely made of ideal mirror. What if a light particle is induced in it by a source of light? Does the light particle remains there by bouncing or disappear after ...
2answers
129 views

### How to calculate reflection profile of a beam shining onto a moving mirror?

I want to build a projector, where a beam of light is shining on to mirrors, placed at different angles, which are spinning fast enough to draw lines. The question is, how to calculate the needed ...
0answers
65 views

### Explanation for strange atmospheric phenomenon

OK, I've seen this strange thing in the sky sometimes. Not all that often, but sometimes. It actually happened tonight. On most nights, at say 9 P.M. it is dark. There might be stars, moon, etc.,...
1answer
288 views

### Are reflection and transmission coefficents real or complex?

Is it common practice to give reflection and transmission coefficients as the ratio of the respective waves with respect to the incident wave when written in complex form or real form? I have seen ...
1answer
80 views

### Can an aluminized blanket hide a person from thermal cameras? [duplicate]

Well, if the person is wrapped tightly I expect the answer is "no", but could an aluminized loose "cloak" hide a person from thermal imaging cameras by reflecting the cold surroundings? Or, if the ...
0answers
154 views

### Reflection and refraction of light [duplicate]

When a light ray strikes an interface a part of it gets reflected, a part of it gets absorbed while another part gets refracted. Why does light reflect? Why does it refract?
0answers
115 views

### Maximum laser power that mirror can handle?

Can I use standard mirrors used for lasers used for laser shows to build some laser that has higher power and is able to burn materials? What are power and power density limitations that cannot be ...
2answers
188 views

### Why does the thought experiment of a photon bouncing of a mirror imply anything for other objects?

Okay, so I am reading a book, "The Elegant Universe" by Brian Greene, which talks about motion and its effect on time. Greene makes the point that time changes with motion by saying that if you have ...
1answer
88 views

### light falling on a completely reflecting friction less mirror

If you had a perfectly reflective mirror whose face was perpendicular to the ground and was kept on a friction less track on the ground, and you shined a flashlight on it, what would happen? Would ...
1answer
2k views

### Laser, wire, and a circle of light

So, when I point a laser at a piece of wire (pointed at a specific angle), a circle of light appears on a wall behind it (see image below). I am trying to see why this happens and if there are any ...
3answers
535 views

### How to understand this symmetry in the wavefunctions of a diatomic molecule?

In Wikipedia (and elsewhere), a particular symmetry of the quantum system of a diatomic molecule is mentioned: symmetry under reflection along a plane containing the internuclear axis. The ...
3answers
396 views

### How to arrange mirrors so I can't see myself?

If I wanted to surround myself with mirrors how would I need to arrange them so that if I stood in the middle of them I couldn't see myself in any reflection? For simplicity let's just say we only ...
1answer
319 views

### Reflection in a cylindrical mirror

Suppose I have a completely cylindrical surface which is silvered on the inside. I want to know what type of reflection takes place when an object is placed inside the ring. Does infinite reflections ...
2answers
3k views

### Huygens' Principle During Reflection: comparing wavelets from before reflection with wavelets from during reflection

I was recently reviewing geometric optics, during which I read about Huygens' Principle and how it could be used to prove the Law of Reflection from the "light is a wave" viewpoint. I'll quote what I ...
2answers
150 views

### Phase change on reflection only 0 and $\pi$ allowed

We know that when a wave on a string is reflected from a hard boundary, the phase change is $\pi$, and from a soft boundary, the change is 0. My question is: this two conditions (hard and soft ...
2answers
291 views

### Basic rule for diffraction

I'm a high school student. I still don't understand the reflection, diffraction and refraction of light. It seems to me that in concept of quantum physics, reflection is just a process of object ...
2answers
731 views

### Rainbow reflected on TV screen? (pic attached)

According to wikipedia, A rainbow is an optical and meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets... Given that we require ...
2answers
365 views

### Why does black glass reflect better than white one?

Why does black glass reflect better than white glass? Both of them are glasses, so they reflect light. But why black glass reflects better? See below, shiny black glass.
1answer
471 views

### How do you calculate the focal point location of a circular mirror? [closed]

I'm trying to find the focal point and center of curvature of a concave mirror. Just using the radius for the center doesn't seem to work. I know C = 2f, but I'm not sure how to find f or C, given the ...