Questions tagged [reflection]

This tag is for questions relating to reflection, the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. A familiar example of reflection comes from water waves; as the waves travel they reflect off objects that are floating in the water, and also reflect off the walls of the container holding the water.

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357 votes
28 answers
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Why are mirror images flipped horizontally but not vertically?

Why is it that when you look in the mirror left and right directions appear flipped, but not the up and down?
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  • 3,757
149 votes
2 answers
17k views

Why does a mirror split my laser beam?

Last night my daughter was asking why a mirror "always does that" (referring to reflecting a spot of light). To help her figure it out, I grabbed my green laser pointer so she could see the light ...
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91 votes
4 answers
15k views

Why does a yellow object turn white under a yellow light? Shouldn't it turn yellow instead?

Recently I was eating a yellow rice for lunch in a restaurant with only yellow lights. But the rice looked white! I was intrigued by this because I always thought it should look yellow since the ...
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  • 1,007
77 votes
1 answer
8k views

Why does soaking a fabric make it more transparent?

It's a well-known fact that when one soaks a thin piece of fabric, it will often become more transparent than it was before. What is the reason behind this? I can't put glass behind the fabric and ...
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76 votes
3 answers
10k views

Why does my beveled mirror make triplicate "ghosts"?

Here is a picture of my power adapter. You can see in has one green LED lit when charging. Now here is a picture of my mirror with beveled edges. When I view the power adapter in the mirror, I see ...
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  • 1,003
74 votes
1 answer
54k views

Why does a window become a mirror at night?

In day, when you look in the room through the window out, you can clearly see what happens outside. At night when it's dark outside but there's light inside you can look in the window but it becomes a ...
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72 votes
9 answers
20k views

Why can't we see images reflected on a piece of paper?

Why can't you see a reflected image on a piece of paper? Say you put a pen in front of the paper, even when light rays are coming from other sources, hitting the pen, reflecting back, and hitting the ...
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53 votes
4 answers
6k views

What wavelengths of light does a banana reflect?

I do know that there are at least two types of yellow light: a light of a single wavelength of ~580 nm and a combination of green light and red light. (Technically, there could be more yellow light.) ...
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  • 723
52 votes
6 answers
76k views

Phase shift of 180 degrees of transversal wave on reflection from denser medium

Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave, when reflected from an optically denser medium? I tried searching for ...
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51 votes
2 answers
7k views

Why are gold mirrors yellow?

Why are golden mirrors yellow? Do they add a yellow component to the spectrum or absorb non-yellow components? If they absorb, then why are they used in telescopes being imperfect? If they add a ...
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50 votes
4 answers
4k views

How can an object absorb so many wavelengths, if their energies must match an energy level transition of an electron?

I believe I have a misunderstanding of some principles, but I have not, even through quite a bit of research, been able to understand this problem. My current understanding of transmission, ...
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  • 613
47 votes
5 answers
4k views

What causes this pattern of sunlight reflected off a table leg?

My friend noticed an interference-like pattern around the table leg. However, we do know that interference patterns of sunlight produces rainbow colours. What seems to be happening here?
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  • 471
45 votes
12 answers
17k views

Why don't we hear sound reflecting from buildings, mirrors, etcetera?

We can see buildings, doors, cars etc. as light falls on it gets reflected to us. but why doesn't the same thing happen with sound? I mean why don't we hear sound reflecting that much?
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45 votes
7 answers
41k views

What is the difference between a white object and a mirror?

I was taught that something which reflects all the colors of light is white. The function of a mirror is the same, it also reflects all light. What's the difference? Update: But what if the white ...
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44 votes
3 answers
10k views

How are classical optics phenomena explained in QED (Snell's law)?

How is the following classical optics phenomenon explained in quantum electrodynamics? Reflection and Refraction Are they simply due to photons being absorbed and re-emitted? How do we get to Snell'...
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42 votes
3 answers
10k views

Why does a mirror reflect visible light but not gamma rays?

Visible light (~500 THz) as well as gamma rays (~100 EHz) are electromagnetic radiation but we can reflect visible light using a glass mirror but not gamma rays. Why is that?
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  • 551
36 votes
6 answers
11k views

If the moon had a mirror surface, would the earth be equally illuminated as by the sun during full moon, or would it require a different mirror shape?

Suppose the apparent diameters of the sun and the moon are exactly the same (which in fact very close to the real situation). If the moon had a perfect mirror surface, would the reflected visible ...
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36 votes
4 answers
4k views

Why are the edges of a broken glass almost opaque?

Unfortunately I broke my specs today which I used in this question. But I observed that the edges are completely different then the entire part of the lens. The middle portion of the lens was ...
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36 votes
4 answers
4k views

Why do photons follow specific path after reflection from a mirror surface if they can be emitted in any direction by electrons of mirror surface? [duplicate]

The electron absorbs the energy of photon(with specific frequency)and re-emits the photon.The photon can be emitted in any direction. So why do they get re-emitted in a specific direction after ...
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34 votes
6 answers
19k views

Why did high quality mirrors use aluminum coatings instead of silver?

I have two questions on mirrors. I’ve read that in the past quality mirrors were coated with silver but that today vacuum evaporated coatings of aluminum are the accepted standard. When I look at the ...
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  • 4,518
34 votes
6 answers
5k views

Why do reflections on a rough surface stretch from the light source towards you instead of spreading out in all directions? [duplicate]

When light reflects off a "flat ground" surface, the reflection stretches vertically but not horizontally (as shown in the pictures below). When light reflects off a "vertical wall" surface, the ...
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  • 589
33 votes
2 answers
3k views

Should a superconductor act as a perfect mirror?

I have been told that metals are good reflectors because they are good conductors. Since an electric field in conductors cause the electrons to move until they cancel out the field, there really can'...
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32 votes
3 answers
9k views

Why is the light reflected at the same angle from mirror?

From the school physics I know that the material objects bounce from the plane surface at the same angle, losing some kinetic energy. In the same school I was taught that the light (and waves in ...
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  • 509
30 votes
12 answers
5k views

Why is everything not invisible if 99% space is empty?

If every object is $99$% empty space, how is reflection possible? Why doesn't light just pass through? Also light passes as a straight line, doesn't it? The wave nature doesn't say anything about its ...
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  • 425
30 votes
4 answers
17k views

Explain reflection laws at the atomic level

The "equal angles" law of refection on a flat mirror is a macroscopic phenomenon. To put it in anthropomorphic terms, how do individual photons know the orientation of the mirror so as to bounce off ...
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  • 637
29 votes
7 answers
5k views

Why don't opaque objects reflect light?

My sister was doing a quiz and I tried to point her in the right direction by giving her scenarios to imagine. One of the questions in the quiz was: Which of the following objects do not reflect light:...
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29 votes
9 answers
37k views

Why do solar panels not have focusing mirrors?

Most of the solar panels that I have seen do not have any mirrors, etc., but usually solar cookers have mirrors. What is the reason for solar panels not having focusing mirrors?
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  • 1,144
27 votes
8 answers
18k views

Why is angle of incidence equal to angle of reflection?

In the Law of Reflection, the angle of incidence is equal to angle of reflection. Why is this true? This is clearly true experimentally, but how does one prove this true mathematically?
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  • 455
27 votes
1 answer
6k views

How are photons "consumed"?

I have very little background in physics, so I apologize if this question is painfully naive. Consider the following thought experiment: an observer is in a closed room whose walls, floor, and ...
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25 votes
2 answers
3k views

What is this blue thing in a photograph of a bright light?

It looks like the bulb of the lamp beside it but how why what
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  • 283
25 votes
3 answers
4k views

Why is the Sun not exactly above its reflection in water?

In this photo, why is the sun not positioned exactly above the "axis" from which its reflection seems to spread? I think it could be how sunlight refracts across the northern hemisphere but I'm not ...
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  • 723
25 votes
3 answers
10k views

Does light reflect if incident at exactly the critical angle?

A lot of textbooks and exam boards claim that light incident at exactly the critical angle is transmitted along the media boundary (i.e. at right-angles to the normal), but this seems to violate the ...
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25 votes
9 answers
19k views

What happens when a photon hits a mirror?

When a photon of light hits a mirror does the exact same photon of light bounce back or is it absorbed then one with the same properties emitted? If the same one is bounced back does it's velocity ...
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  • 1,559
24 votes
7 answers
16k views

Are infinite reflections between two mirrors really infinite?

As written in the title it's a somewhat rhetoric question, so let me be more clear. Let's say I have two mirrors facing each other. They are perfectly aligned and perfectly reflective. I'm looking ...
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  • 341
23 votes
2 answers
5k views

Why does my watch act like a mirror under water?

I have a digital watch, rated to go underwater to $100 \rm m$. When it is underwater it can be read normally, up until you reach a certain angle, then suddenly, it becomes almost like a mirror, ...
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  • 3,087
22 votes
7 answers
10k views

Does real life have "update lag" for mirrors?

This may sound like a ridiculous question, but it struck me as something that might be the case. Suppose that you have a gigantic mirror mounted at a huge stadium. In front, there's a bunch of people ...
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22 votes
5 answers
18k views

Why is the surface of the Moon white?

Why is the surface of the Moon white? Rather, what makes the surface white?
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22 votes
5 answers
5k views

Does a well-lit mirror weigh more than an unlit mirror?

If you weighed a mirror in a room with no light, and then weighed a mirror in a well lit room so that the mirror reflects light, would the weight be different?
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  • 231
22 votes
5 answers
1k views

What longest time ever was achieved at holding light in a closed volume?

For what longest possible time it was possible to hold light in a closed volume with mirrored walls? I would be most interested for results with empty volume but results with solid-state volume may ...
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  • 10.6k
22 votes
3 answers
6k views

Why is sound reflected and not transmitted through a wall?

We know that speed of sound is higher in a denser medium. So when a sound wave strikes a wall, why does it echo instead of passing through it with a speed faster than the speed of sound in air?
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22 votes
4 answers
8k views

Why can't my eye see itself in the mirror through polarizing 3D-glasses?

I found a pair of polarizing "3D glasses" lying around, and tried to look at myself in the mirror while wearing them. To my utter confusion, when closing the left eye and only looking through the ...
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  • 322
22 votes
1 answer
4k views

Why does the spotlight reflected off of a rectangular mirror tend to become circular?

Background and setup When I was 12 I used to like a girl, we were almost neighbors and it was essential that our parents don't find out. So whenever one of us wanted to call the other they'd signal ...
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  • 1,588
21 votes
2 answers
14k views

Why does sunset over a body of water cause a path of light stretching towards the horizon?

Have you ever notice the sunset's image in the sea? It's like long light path to the end of the horizon! I've attached a sample of this: How can we explain this? I know that it can happen even in ...
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  • 307
21 votes
2 answers
14k views

Why is reflected light polarised?

Why is reflected light polarised? I have learnt about Brewster's angle, and how at a particular angle all light reflected is polarised, but do not understand why. Is this something that could be ...
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19 votes
2 answers
11k views

Would you see a rainbow from refraction when the sun is in front of you?

I know how rainbows are formed, and why. Usually it is said that the Sun must be behind the observer, in order for its light to be totally reflected inside the droplet and then reach the observer. ...
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18 votes
7 answers
6k views

Can light continue without a light source? [duplicate]

If you have 2 mirrors over for each other placed exactly so they face each other perfectly, and then use a laser light pen as the source into one of the mirrors so it bounces to the other mirror and ...
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  • 191
18 votes
1 answer
2k views

Why should the back of a parabolic mirror be painted black?

This video (a bit after 2:00) says that the back of the parabolic dish should be painted black before applying the Mylar over it. The purpose of the mirror is to concentrate all the light hitting its ...
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  • 291
18 votes
5 answers
12k views

Wave reflection and open end boundary condition intuition

I need to understand one seemingly simple thing in wave mechanics, so any help is much appreciated! When a pulse on a string travels to the right toward an open end(like a massless ring that is free ...
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18 votes
2 answers
2k views

Why are so many different types of objects white, yet appear gray when they are wet?

There are many things with different textures that appear white – salt, beer foam, paper, shaving cream, snow, talcum powder, white paint, etc. The most common answer is all of the frequencies must be ...
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  • 235
17 votes
3 answers
8k views

Is it possible to 3D print a mirror to create a high quality telescope?

Is it possible to 3D print a mirror with todays available materials? If so, would there be a reduction in image quality?
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