# What is Reflection: Definition and 948 Discussions

Reflection is 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. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected. Mirrors exhibit specular reflection.
In acoustics, reflection causes echoes and is used in sonar. In geology, it is important in the study of seismic waves. Reflection is observed with surface waves in bodies of water. Reflection is observed with many types of electromagnetic wave, besides visible light. Reflection of VHF and higher frequencies is important for radio transmission and for radar. Even hard X-rays and gamma rays can be reflected at shallow angles with special "grazing" mirrors.

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1. ### Mirror system in geometrical optics

I tried solving it in this way, distinguishing 3 cases and passing the first ray through the point located at a greater distance from the vertex of the angle formed by the two mirrors: 1) the angle of incidence of the ray on the mirror inclined 45° to the horizontal is 45° or 0°: in the first...
2. ### B Sunlight reflection on planets

If the Sunlight lets say would go off, exactly how long would astronomers on Earth still see sunlight reflected on the surface of Mercury, Venus, Mars, the asteroids, Jupiter Saturn, etc.? I mean Sun goes dark at 0:00 from the point of view of Earth-based observers. At that exact moment, if...
3. ### B Mapping wave forms to sphere, does wave form y=0 have a reflection?

Zero does not have an inverse. And y=0 does not have an inverse. Does the wave form y=0 for all x have an inverse?
4. ### I Mirror rotates any polarisation by 90°?

Over each eye is a linear polariser and they are orthogonal to each other. So I conclude from the experiment that the polarisation must have been rotated by 90° by the mirror. That reminded my of phase plates but they only work because their refractive indix depends on the angle. Along two...
5. ### Air wedge - why is reflection from top of first slide ignored?

My textbook derives the condition for bright and dark fringes on an air wedge by assuming that the reflected and refracted rays have a path difference of pi. Hence the conditions for bright and dark fringes end up being the opposite of what is expected. However I did not really understand the...
6. ### I Reflection, refraction, and Snell's law

Where do the laws of reflection, refraction, and Snell's law come from in geometric optics? Are they derivable from basic laws of physics?
7. ### A Iphone Reflection has a pattern

Hi all! I'm sitting in the office on what would normally be a dive day so I'm slightly over observant. The sun is coming in heavy through my window, and holding my iPhone I began playing with the reflection on my office wall it produced. The reflection at first was no different then any light...
8. ### I have a question about the mathematical model of a reflective curve

Hello : Have a question regarding the mathematical model of reflective curve where could i find information on it ? (pdf , webpages , ebooks ,...etc ) Other than Wikipedia Best Regards HB
9. ### B Space, Reflection: See Earth's Past in Mirror?

can you theoretically put a mirror in space, take a photo of earth/dirts reflection and see it in the past?

11. ### B Parallel light reflection for a one-way speed of light measurement setup

Hello, Is there a mirror that will reflect light in parallel trajectories ? If yes, is the reflected light in sync, and will all beams hit a flat surface simultaneously ? Thank you
12. ### The magnetic phase change of an electromagnetic wave during reflection

If the question had mentioned ##\overrightarrow{E}## instead of ##E_\bot##, then we could have used ##\overrightarrow{B}=\dfrac{1}{v}\widehat{k}\times \overrightarrow{E}## to get the direction of the magnetic field. But the question had only mentioned ##E_\bot##. To my understanding, knowing...
13. ### I Reichenbach Synchronisation: Proving i=r

I use Reichenbach synchronisation. The one-way speed of light (OWSOL) in the x and y-direction is ##\frac{c}{2\epsilon}## and in the reverse direction it is for both ##\frac{c}{2(1-\epsilon)}## such that the average round trip speed of light is ##c##. For any choice of ##\epsilon## the physical...
14. ### Reflection of sound wave in an open organ pipe

I know that standing waves form in an open organ pipe. Since, standing waves can only form from superposition of original wave and reflected wave, so there must be a reflected wave in an open organ pipe. But I fail to understand how sound wave can reflect at the open end of organ pipe.
15. ### A Reflection Instant? Atomic Level Causes Explored

What causes reflection on the atomic level? I believe that the interactions of light and the electrons of a body take at least very very small amount of time. The time is probably negligible but does that time even exist or does the reflection instantly happen.
16. ### B Reflections on Reflection

For quite some time I was under the mistaken impression that the specular reflection of objects from the calm surface of still water forms an image that is the same as the image I see except it's upside down. That is not the case. In the picture below* I have circled in white a couple of...
17. ### I The reflection of the sunset on the water is redder--Why?

I presume that some kind of absorption occurs when the sunset is reflected on the water, but can anyone describe this in more detail?
18. ### I Interference by reflection on a CD

A fairly focused beam of light incident on a CD projects a clearly visible interference pattern onto a screen. May I infer that it has good (or at least enough) spatial coherence? This property is evident, for example, in a lens-focused beam of light produced by a LED or by a ray of sunlight...
19. ### Exploring Wave Reflection: A Mathematical Journey

I know for a wave moving from left to right, ##\psi_i = Ae^{i(\omega t - k_1x)}## The first reflection where ##Z_1## is ## R_{12}Ae^{i(\omega t - k_1x)}## The second reflection. The wave moves from 2 to the limit between 2 and 3 then reflect... Thus, ##T_{12}R_{23}T_{21} Ae^{i(\omega t - k_1 x...
20. ### Analogy between EM wave reflection and S-parameters

It is well known that one can solve incident an reflective wave in homogeneous linear media by matching PDE boundary conditions. In the electrical engineering community, one solves similar problem using smith chart and scattering parameters for 1-dimensional propapation of TEM modes in...
21. ### Simulate mach reflection with mach stem generation using Ansys Fluent

I need to simulate mach reflection with mach stem generation using on Ansys Fluent. The wedge angle is of 22deg at Mach 5.
22. ### Complex Reflection and Transmission Coefficient in oblique incidence

Hello, Something has made me confused after studying the Snell equations these days. Regarding the Balanis Advanced engineering electromagnetic( the pages have been attached), and based on that the reflection and transmission coefficient can be complex I need to rewrite the (5-23a) again...
23. ### Angle of incidence and total internal reflection

the angle of incidence at A is 40°, then why did the answer key say "angle of incidence at A is just less than 90°". it is obvious that 40° is quite far from 90° right?
24. ### Reflection and Refraction in an Elliptical Imaging Mirror

My thoughts so far: a. Since the critical angle occurs at the origin for the given parameters I would imagine that the maximum power reflected would be 100% since at the critical angle ##\theta_t = \frac \pi 2## and ##r_ {\perp} = r_{\parallel} = 1##. I do not know how I might go about finding...
25. ### Fish Reflection: Analyzing Light's Interactions with Water

So first I looked at where the image of the fish appeared to be when it went through the water surface. since we can assume the water is flat, R is infinity, so n1/p=-n2/q. plugging in the values (n1=1.29, n2=1, p=3.5) I get q=-0.3686. So the image of the fish appears at 0.369 above the...
26. ### A potential well with 3-fold reflection symmetry

When we are talking about Bloch's theorem and also the tight-binding approximation, we can use them to help finding eigenstates of a system. However, I am so confused how to apply it in this case (below is my homework) and don't even know how to start it... All I understand about the Bloch's...
27. ### Double Glazed Window Reflection

I hope this is not a stupid question but I attach a photo of a reflection of a square double glazed window showing on a wall opposite the window. Could someone please explain to me what is happening here. I presume the outer circular reflection is showing the extent of the suns rays and the...
28. ### Prove the reflection and transmission coefficients always sum to 1

Consider polarized light crossing a sharp boundary between two volumes, each of a different but uniform refraction index ##n_1## or ##n_2##. Prove that the sum of the transmission and reflection coefficients of this light ##R+T=1##, where R \equiv {I_R \over I_I} = \left( {E_{0_R} \over...
29. ### Reflection of Radio Waves by a Mirror-like surface

Hey guys, I'm new to the physicsforums. I wanted to share some videos I made and see if anyone was interested or wanted to discuss what they see. In this video I show in a manner in which is VERY easy to see, that a reflective surface will reflect not just light but also radio waves (and most...
30. ### Deriving the Law of Reflection from Huygens Principle

Attached is section 33.7 from my book, which introduces Huygen's principle in order to derive the law of reflection. I am more used to the ray model rather than the wave model, so I'm constantly going to try to relate everything back to rays. Making this connection also helps with completeness...
31. ### Questioning My Thinking: A Reflection

I started to do this, but I'm not sure my thinking is good.
32. ### EM Wave Reflection and Transmission Between 3 Materials

Hello there. I set up the problem like this, I have a wave incident from air on the anti-reflective coating consisting of: ##\tilde {\vec E_I} (z,t) = \tilde E_{0_I} e^{i(k_1z- \omega t)} \hat x## ##\tilde {\vec B_I} (z,t) = \frac 1 v \tilde E_{0_I} e^{i(k_1z- \omega t)} \hat y## This wave gets...
33. ### Reflection of inverted waves to form a standing wave

Standing waves in a string fixed at one end is formed by incoming and reflected waves. If reflected waves are 180° out of phase with incoming wave, how could they combine to give an oscillating wave? Shouldn't it be completely destructive interference all the time across the whole length of string?
34. ### Contradiction in Phase of reflected sound

While studying the fundamentals of sound waves in organ pipe, I noted that the fact about phase of reflected waves is contradicting while referring multiple sources This book of mine describes the reflection from a rigid surface/closed end to be in phase Whereas this one describes the...
35. ### Frequency and Sound Wave Reflection

I got that the sound wave will take 0.3s between the student and the left wall. It takes 0.5s between the student and the right wall. The first time these waves will coincide is 1.5s (5 trips for left side and 3 for right side). I then did 1/1.5 to get 0.67Hz. However, the answer is 6.67Hz. I'm...
36. ### Angle of reflection of a beam light on a moving mirror

Before to open this topic, I found this there. It's quite similar, if not the same, but I'm a little confused, so I'm here. The situation is represented in this image. From optical geometry, ##\theta_{incident} = \theta_{reflected}## The four-momentum in ##S'## is the following one...
37. ### Engineering Voltage pulse sketches for reflection on a lossless transmission line

Hi, I was recently attempting a question about transmission lines and I don't seem to really understand how the voltages travel through the line. Question: If we send a voltage pulse of amplitude ## V_0 ## through a lossless transmission line, what does the voltage at the output look like when...
38. ### Is Reflection of an Incident Wave Lagging or Advancing?

Actually, maybe i am confusing something, or valuing unnecessary things, but this doubt arises and i am not sure how answer it. The reflection of an incident wave changes (suppose it will change, we don't need to talk when or why to go on the discussion) by π rad, but, this reflection lags the...
39. ### Radar Reflection: Charged vs Non-Charged Objects

A question I’ve been trying to figure out for the last 5 years with a friend of mine: Would the radar reflection from an object be different if the object is charged or not charged?
40. ### Problem with reflection and transmission of waves

See, to illustrate: Let's suppose there is an incoming wave by x < 0, what is the problem? It will find a bead in the string, so: , x < 0 , x > 0 T and R are the transmitted and reflected coefficients. Now suppose there is another bead in x = L. The problem is what happens 0 < x < L: The...
41. ### Reflection and transmission of waves in a medium of nonuniform density

Hello all, Apologies in advance for the text-wall; this is a rather involved question. I am trying to compute the effective transmission coefficient for a medium of non-uniform refractive index. For simplicity I am assuming the slab has thickness ##d##, that ##n(0)=1##, and that ##n(d)=n##...
42. ### Classically, how can I explain Reflection?

Hello guys! I was trying to understand (without involving too much QM) how does reflection works, and why metals reflect almost 100% of visible light while glass does not, and also why when we increase the frequency, metals become transparent. I know that when any single photon reaches a body...
43. ### Understanding Reflection of Light on a Concave Mirror

My Basic Question is- Why can we see our inverted and real image inside a concave mirror when the image is formed in front of it and not behind? If you say that our eyes tries to image the real image formed by mirror on the mirror itself then- Imagine a situation where we have a concave mirror...
44. ### How to explain TE20 mode in a rectangular waveguide from reflection

In Feynman's lectures, he explained the ##TE_{10}## mode of waveguide by considering a line source in the middle of waveguide as below: since the adjacent sources are all out-of-phase, which means to have interference, the adjacent optical path would be about half of wavelength as below: where...
45. ### The possible plane separation related to Bragg reflection

2d sin q = nl d = nl / (2 sin q) d = (1 x 0.16) / (2 sin 30o) = 0.16 nm But 0.16 is not in the option. And how to find other value of d? Thanks
46. ### Internal reflection equation question

As you can see we have 3 media here. Only focus on the glass and coating medium. Assume an incident ray comes from the air medium and is refracted inside the glass and then it is refracted again in the coating medium. The x angle is the angle inside the glass medium. In this case, if the...
47. ### B Compressing Light: Reflection in Small Gaps

Hi there Let’s consider a photon of wavelength λ is being reflected across of gap d meters. The photon is a reflected back and forth between the same points on two horizontal sheets that reflect 100% of the light. What happens when the distance is smaller than wavelength? Thanks
48. ### Frustrated Total Internal Reflection

I've been reading into - and watching videos on - FTIR as an explanation of Quantum Tunnelling. The articles and videos I've watched switch between classical and quantum systems so frequently its left me with a question I can't find an answer to - the texts that seem like they might answer it...
49. ### Light Reflection and Particle Size

I'm studying particle counters and one of the detection methods uses reflected light to determine the sizes of the particles. What principle does it base on? Thanks!
50. ### Second reflection angle of incidences in 3D

Given Theta1(angle of incidence) and alpha1(azimuth angle). how do we obtain the second reflection angle theta3 and alpha3? Assuming the surface to be a mirror reflection(theta1 = theta2). Need an equation when varied the incident angles we would obtain the second reflection angles or a method...