I was filling the bathtub the other day with water and noticed something. When calm, the light illuminates everything and I can see the sides and bottom of the white tub without shadows. Then, when I add a droplet of water its ripples (either its peaks or valleys of the wave) cast concentric rings of shadow which travel about 2 feet per 3 seconds (0.2 m/s) outward from epicenter.   I'm wondering what exactly creates these shadows. That distance is too large for light waves destructively interfering.
122703
Take a look at the following picture:   Why does the light at the bottom of the water form this pattern? I have also seen the same phenomenon in all the swimming pools I've ever visited, of whatever depth they may be. How does this happen?
61775
My professor asked an interesting question at the end of the last class, but I can't figure out the answer. The question is this (recalled from memory):  There are two travelling wave pulses moving in opposite directions along a rope with equal and opposite amplitudes.  Then when the two wave pulses meet they destructively interfere and for that instant the rope is flat.  Why do the waves continue after that point?  Here's a picture I found that illustrates the scenario    I know it's got to have something to do with the conservation laws, but I haven't been able to reason it out.  So from what I understand waves propogate because the front of the wave is pulling the part of the rope in front of it upward and the back of the wave is pulling downward and the net effect is a pulse that propogates forward in the rope (is that right?).  But then, to me, that means that if the rope is ever flat then nothing is pulling on anything else so the wave shouldn't start up again.  From a conservation perspective, I guess there's excess energy in the system and that's what keeps the waves moving, but then where's that extra energy when the waves cancel out?  Is it just converted to some sort of potential energy?  This question is really vexing! :\
113906
Why is light produced when an underwater bubble is collapsed with a sound wave?  I have come across this fact on a page () but can't understand "Why". I'm just curious about this interesting fact. And, I want to know what's the currently accepted model for this phenomenon and how good it holds. Any kind of help regarding this topic will be highly appreciated.
17188
I think every single one of us has experienced a dark dot in his/her sight when looking at a white surface such as a white ceiling, there's something in our eye that with a little focus we can see it, and when we move our eyes around, that thing floats around quickly in your sight. It's like a substance on eye's surface, I want to know what is it called. Hope I'm clear enough.
92368
I'm wondering how to achieve a neon-light type effect. For example, in :    Or in :    Is that a Bloom Effect? Or what techniques would I have to look for?
42632
I was laying on my bed, reading a book when the sun shone through the windows on my left. I happened to look at the wall on my right and noticed this very strange effect. The shadow of my elbow, when near the pages of the book, joined up with the shadow of the book even though I wasn't physically touching it.   I have posted :The video seems to be the wrong way up, but you still get the idea of what is happening.  What is causing this? Some sort of optical illusion where the light gets bent?  Coincidentally, I have been wondering about a similar effect recently where if you focus your eye on a nearby object, say, your finger, objects behind it in the distance seem to get curved/distorted around the edge of your finger. It seems awfully related...  EDIT: I could see the bulge with my bare eyes to the same extent as in the video! The room was well light and the wall was indeed quite bright.
35222
Recently I downloaded blender 2.8 for the new real-time render engine, but then I found out that the shadow in the eevee is really unexpected. Just like shown above, the quality of the shadow is bad and the movement of the shadow is also strange when I move the object. The lamp is a sunlight, and the sphere and the plane are just preset meshes. Could you tell me what adjustment do I need to create a normal shadow?
4960
My model has a clear plastic (or glass) dome with objects inside.  The objects appear dark.  I've tried the glass shader with color 100% RGB, with very small IOR, and using just a refraction shader.    I know Cycles has problems with caustics, but I just want broad illumination to fall clean through the glass.  The light-to-column path can ignore refraction, but is blocked or tremendously attenuated. The camera-column path needs refraction, and seems to work fine anyway.  This demo image offers all optical paths of interest:   light upon object, seen directly light upon object, seen through glass (looks okay) light through glass onto object, seen directly. This is the shadow on the lit side of the column just below the glass tubing.  I expect full illumination, but there is shadow.  There is some light, but it's diffuse light from the floor. light through glass onto object, seen through glass. This     I did at one point try non-progressive rendering, and find extremely coarse light where there shouldn't be shadow, but this is not a practical way to make nice images. I've even tried cranking up certain sampling settings to many thousands, but still get bad noise though less, at the cost of long render times. I  would like to finish my creations sometime before "Star Trek, the Generation After the Next" becomes real life, if you know what I mean.  The next image is an example. I think Transmission in Sampling was 5000, but not sure.    I'm using Cycles in Blender 2.67 on a quad core Linux machine, 16GB RAM. Machine limits have never been a problem for 3D rendering.  Possibly, I screwed up some setting when I made my startup file, and just need to fix it. OTOH maybe this is just a limitation of path tracing, or of the way Cycles does it. If that's the case, what to real-world Blender artists do when they need to produce images on a budget and schedule?  What is the practical real-world fix?
116461
It stands to reason: if it didn't, the entire sky would be covered with stars shining blindingly day and night.  But what causes a light wave (or an electromagnetic wave) to fade if there are no celestial bodies in its way? Or, alternatively, why doesn't it fade sooner? Some stars are visible to the naked eye that are hundreds of light years away. Others, closer, can only be detected with the aid of a telescope. Why?
80739
A  is formed when a raindrop refracts light, but why then does the whole sky not become a huge rainbow when it rains? Would the light not be dispersed into ordinary white light? What causes it to look as if each end is nearly touching the ground?
11449
I am following this  on making an asteroid and when it comes to rendering the scene I get an unwanted "shadow". The shadow starts to appear in frame 36 of the render (but is clearer in frame 40) and i do not know what i have done wrong. Here is the .  The effect described here is clearly visible in the right top corner, like a polygonal darkness.
102515
This is a common problem I've found in a few jobs related with ocean. When the camera is close to the surface, looking at the horizon, those black areas appear. Either with a normal texture or not.     It looks there's a problem with ocean's self reflection, but I can't avoid this by adjusting the bounces. Any ideas?  . As you can see, the environment is visible only through camera and glossy, and the problem keeps with a blank environment too. The scene is lit with a sun lamp and plain color environment.
120247
I have a set of concave/convex mirrors/lenses, and I have drawn out all of the ray tracing diagrams for each possible combination and type of image each optical element can produce. When I look at the ray tracing diagrams then reproduce the situation in the real world with myself as the &quot;object&quot;, all the scenarios make sense to me except one: when I as the object stand beyond the focal point of a concave mirror.  The image ends up as &quot;real&quot; and appears to be in front of the mirror. Now I understand that in the situation above, I as the object would stand at 6m and this would result in the image appearing at 12m. So if I placed a wall or screen at the 12m mark, the image would form on that surface (just like a movie theater screen).... at least I think I interpreted that correctly. But I still see myself when I look in the mirror?! If the image is supposed to form and come into focus behind me, what in the world am I seeing when looking at the surface of the mirror? I still see myself, just inverted. The surface of the concave mirror still has a reflection on it. It doesn't look quite like a normal flat mirror, in that the image doesn't really look like it's &quot;inside&quot; the mirror, more like it's right on the surface of it. It's really frustrating because every other possible arrangement of optical elements makes total sense to me, except this one. Any suggestions on how to think about it? Thank you for your time!
83305
From the article that I read on physics classroom website on rainbow, rainbow is formed with red on the top and violet on the bottom because violet refracts more, and has a smaller angle of deviation and red refracts less and has a bigger angle of deviation. So the red light rays come out of the water droplet steeper than do the blue rays. This steepness requires you to look higher up in order to see the  red part of the rim.  Here is also an  I saw of my question on PhysicsSE.  But the answer to that question doesn't really answer my particular question about the concepts of the formation of rainbow.  Two questions:   Water droplets being so small, and the width of rainbow so big, how then is the whole rainbow still shown in ROYGBIV, but not composed of rainbows of smaller width, the colors of each too shown in the order of ROYGBIV?  What is described in the PhysicsClassroom seems to only work for the very top portion of the entire rainbow that is horizontal. I don't see how it would work for the vertical portion, the part where the rainbow starts from the ground. At this portion, the observer does not have to change his/her angle of viewing in relative to the ground in order to see the two (violet and red) extremes of the color band.    please attach a picture of a single droplet and how rays from the Sun comes in and out of the droplet and into the observer's eye.
17940
So, I am not sure I can reproduce it via images, but the steps are:  1) At night, open a window and have a look at the surface of the earth  2) Suppose there's an object that reflects a tiny amount of light  3) When you actually try to focus your eyes at this object, you either don't see anything (depends on the amount of light it reflects) or you can hardly see it  4) When you focus your eyes on something that is 3-10 metres away, you can easily see this object with your ambient vision. Not the details, but it seems that it reflects more light.   Why does it happen?
115536
How would I go a about making volume light beams?  I have have tried  various tutorials, but they must be for a older version. as applying them does seemingly nothing.  A link to a functioning tutorial would be greatly appreciated as well.  I don't have a picture or .blend to show, as my problem with atmospheric lighting does not pertain to any specific scene.
116244
In the double slit experiment we have something like this     Light waves from two sources interfere at screen to give us this pattern. To reach the middle (that is a point on the perpendicular bisector) of measurement screen waves will travel equal distances (at sources they are in phase because of the same main source) and hence will be in phase at the middle of the screen and hence a constructive interference will occur.    We can write things a little more mathematically, if at time $t$ the crest of the light wave is at the sources (secondary) then at time $t+nT$ ($T$ is the time period) crests will be at the middle of the measurement screen and hence a maximum will occur. Here, I have assumed, for simplicity, that distance between the source $S_1$ and the middle point M is $n\lambda$.    Now, my question is when there was a crest at $S_1$ and $S_2$ then we had a maximum at $M$, but when there is no disturbance at sources (I mean $E(t)=0$ and $B(t)=0$) then there should be no disturbance at M too and therefore we should obtain a dark fringe (no light) for this particular interference. Why does the interference pattern remains static? The bright fringes should be turning on and off periodically.    My question comes down to normal light also, why do we see the light even when the electric field and magnetic field components reach their zero position periodically? We should see light as being turning on and off, off when $E(t)$ and $B(t)$ becomes zero and on for every other time.    P.S. :- My $M$ in the figure doesn't coincide with the maximum but by $M$ I meant the middle of the screen where the first maximum gonna occur.