Why does a wave reflect on the edge of an open tube? There is nothing solid to make the wave bounce.  Then why is it reflected?
38039
How can standing waves be produced in an open organ pipe even though both of its ends are open? Can someone explain with more clarity?
25149
This example purports to show reflection of light rays from a spherical mirror. It looks good, until you try to draw a ray from the tip of the candle flame, then through the focal point, $F$, and then emerging parallel to the optic axis $(CF)$.  Go ahead, draw it on your computer monitor screen, or print this page and draw it on the paper. Whoops! This ray should then pass through the image of the tip of the candle flame, but it doesn't!  Here's what you get when you draw the third light ray (in red) from the candle flame. It comes nowhere near the image of the candle flame. As soon as you draw some of the "missing" rays, you discover that the diagram becomes inconsistent.    According to me, the diagram seems to be perfect. From where did this anomaly come from? Please help.
56669
So I've been reading a bit and watching some videos about the double slit experiment, and therefore the wave particle duality; I've also read this "implies" that a particle can be in two places at the same time. Can you clarify this, and how could that be possible?
59333
Please consider the following derivation of the wave equation:    Questions:   I am just starting to learn about waves so this might be trivial. In the above, why are we interested in the transverse force which seems to be defined as the component of the tension force (which I am assuming is the force in the direction of the curve of the string) in the $f$ axis direction? Why is the wave equation modeled on the vertical displacement of this line segment under tension force?  Lastly, is this supposed to model a fixed profile wave moving at a constant velocity? Or is the string supposed to change shape as a function of time? What is the geometric interpretation?
23265
Suppose I have two counter-propagating travelling waves of the same frequency but of different amplitude, like the transverse waves produced in a string by partial reflection off an endpoint.  I read that we will get a mixture of standing and traveling waves, and I can see the theoretical part, but what does this mean, exactly? What are the nodes now? Also, can I now say that energy between loops will be non-transmitting? Because now we have both a traveling and a standing wave.  If possible please provide a picture for better visualization.
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Firstly, I apologise if my thinking is completely incorrect - I am by no means a physicist (yet!), I have included layman illustrations to hopefully assist in explaining my thinking.  I am imagining the big bang to be, for lack of a better word, an explosion, thus the universe to be progressively expanding:    Therefore, to me it seems logical to suggest that there is an edge.  If this is the case, then is it reasonable to suggest that explosion + edge = 'bright edge'? Where light projects in all directions at the edge, not just outwards into the 'nothingness'.     So, this brings me to my question: why, when someone looks deeply enough 'at the edge' do they see an absence of light?   Again, apologies if I'm jumping to irrational conclusions &amp; am way off.
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The mirrors we use everyday have a highly reflective smooth surface, so that we can see a clear image.  But I found the same happens on a rough (not so smooth) surface, though only at shallow angles.  For example    this is the logo of physics stackexchange, reflected from the back of an ipad.  Considering that aluminum may contributed to reflection, I tried a different material:    this time a piece of printer paper.  Though not as clear, there is still some visible pattern resembling the logo.  The same effect can be observed on highways, where distant vehicles have a mirror image off the road; I do not have a picture at hand however.  So, why is this happening, and why only on shallow angles?
112329
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 through one of them (using the one-sided mirror effect) and see what seems to be infinite reflections.  If I look closely at the vanishing point, I obviously can't see very well what goes on there, because the reflections are too small. My question is, are there other limitations?  a) If I look close enough to the vanishing point, is there a point at which the light would have to travel too much distance to reach me that no photon would actually make it?  b) If I start looking immediately after turning on the light, it should take a tiny amount of time until all the reflections are created, i.e., it takes time for light to do all the back and forth trips it takes to create the very small images. How good a microscope (telescope?) would I need to be able to see the image being created? That is, to look at a spot and see nothing, and then some epsilon of time later see an image appear.
84696
There is a  being thrown out of a flask, literally hovering out of the container  My question is how detailed a physical explanation of this phenomenon we have?  Question: More precisely, if we used the best available mechanical physics simulator software, and we tried to simulate this behavior, would the software be able to reproduce the effect or not? My guess is not but I would like to know why not.  Or do we have to content ourselves only with handwaved explanations? I am from the school of thought that you don't understand physics until you have a reasonable certainty that you can reproduce the physics in a computer.
51952
I have a problem with energy conservation in case of interfering waves.  Imagine two harmonic waves with amplitudes $A$. They both carry energy that is proportional to $A^2$, so the total energy is proportional to $2A^2$. When they interfere, the amplitude raises to $2A$, so energy is now proportional to $4A^2$ and bigger than before.  The equivalent question is what happens to the energy with the superposition of two waves that interfere destructively.  Also, if someone could comment on the statement about this problem in my physics book (Bykow, Butikow, Kondratiew):      The sources of the waves work with increased power during the interference because they feel the wave from the other source.
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This is a simple experiment that anyone can do at home. Open your tap so that the water maintains a laminar flow, and the cross section of flow is considerably thin. Place your finger 3-4 cm below the flow. A beautiful wave-like pattern is observed on surface of flowing water, near the region of your finger. Changing the position of finger changes the 'wave-length' of the wave.   The attached picture shows how to do this experiment, though the resolution is not clear.    What is the explanation for this phenomena? Probably a harder question would be if there is an intuitive explanation for it. Thanks!      ${\bf Edit:}$ I observed a similar phenomena in the swimming pool...when the water is still, move your hand slowly along the surface of the water. It causes a 'bump' in the water, which decays away in a wave-like pattern in front of your hand. Clearly they are the same phenomena: water falling on the hand or hand moving against the water.  The answers below are very interesting (Thanks!). And as far as I can see, they are still being debated, suggesting that the phenomena is more non-trivial that it appears to be. I had accepted an answer earlier, but I am now taking it back, as I did not completely understand it. Looking forward to further discussion on it. It would be most exciting to find an answer that is elementary: without resorting to complex terminologies of fluid mechanics.
49232
Light has always been a mystery for me. When we do a simple experiment of holding a lighter in one hand and a light source behind it, it shows no shadow on the wall at all. Why is this happening? Is it because the flame is pure energy and doesn't have matter in it, or is it due to light passing through the flame and not getting reflected? If it is, why isn't the light getting reflected or retracted?
13439
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 it but everywhere the result is just used.The reason behind it is never specified.
97228
At what pressure will be particles in a medium be unable to form a sound wave when disturbed? How can this pressure be described mathematically?  My guess is that this would correspond to the point at which the restoring force due to pressure is unable to create a transverse wave and the disturbed particles travel infinitely far away before the hypothetical wave reaches it's amplitude. But I have no idea how you would even begin to start finding a quantitative value for this point.
80874
I would like to to create the image above. I have tried to make multiples layers of the waves and edit it's opacity but it does not seem to work. I would really appreciate some feedback and guidance. Thank you.
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I have looked online to no avail.  There is two competing answers and I am curious to know which one is right.  Someone asked me this question.  If you are traveling at the speed of light can you see your reflection in a mirror in front of you?  My answer to the question is no, I would figure that in order for that to happen the light reflecting off you that would appear in the mirror must travel faster than the speed of light to actually reach the mirror (which we all know is impossible).  He says the answer is yes, that it is all relative to the current frame of reference.   Can anyone validate the correct answer with possible references?
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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 read in the book for Huygens' Principle (from Serway and Beichner, Physics for Scientists and Engineers with Modern Physics, 5th Ed., Vol. 2, pg. 1119): "In Huygens' construction, all points on a given wave front are taken as point sources for the production of spherical secondary waves, called wavelets, which propagate outward through a medium with speeds characteristic of waves in that medium. After some time has elapsed, the new position of the wave front is the surface tangent to the wavelets." The authors go on to show that using this principle for a plane wave shows that at any later time a plane wave is still a plane wave. Likewise, Huygens' Principle can be used to show that a spherical wave front remains a spherical wavefront at any later time (again assuming the light is not interacting with any surface). (See, e.g.,  for a couple of figures.) Next, the authors apply Huygens' Principle to prove the Law of Reflection. However, they don't actually draw the wavelets, so I tried it myself (and I failed the first couple of times).  What I've learned by thinking about this for a while boils down to this: to understand reflection via Huygens' Principle, the wavelets you are to use for drawing the tangent wave front must all originate during the reflection process (see Figure 1 below). This seems quite reasonable to me. If I want to know what happens after a reflection, I should use wavelets that form during reflection. However, one thing that feels strange to me is that these secondary wavelets are all formed at different times, and then I'm using information from all of them at the same time to draw a reflected wave front. If, during the reflection process, it's ok to use wavelets that form at different times, then when is it ever not ok to do that? For example, if I try the same trick (of drawing secondary wavelets that originate at different times and then using all of those wavelets at the same time to find a new wave front) with a plane wave, I seem to get a result that makes sense (see Figure 2 below), even though the way I'm using Huygens' Principle in this case does not make sense (I have to have knowledge of how a plane wave propagates to make Figure 2, but the point of Huygens' Principle is to show us how the wave propagates in the first place).      With these examples in mind, if I naively start drawing wavelets that originate at different times (some before and some during reflection), I can get the following figure, which doesn't show me how reflection works. Why is that? I must be missing something fundamental about Huygens' Principle, or maybe it's a problem related to the $180^\circ$ phase change that occurs during reflection (so that wavelets that formed before reflection are out of phase from wavelets that form during reflection)?