# What is Interference: Definition and 1000 Discussions

In physics, interference is a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude. Constructive and destructive interference result from the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency. Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves, gravity waves, or matter waves. The resulting images or graphs are called interferograms.

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1. ### Show that the minimum in alpha-decay spectrum is caused by interference of peak

This problem set considers (beta-delayed) alpha decay of ##{}^{20}Na##. I'm currently stuck in the following exercise and was hoping some of you could help me in the right way. Thanks in advance! The problem is: c) The experimental spectrum of ##{}^{20}Na## can be found below. Apart from peaks...
2. ### I How Big is a Photon?

This YouTube video, with the same title I have given this thread, reports on an experiment. He sets up an interference experiment. The light source is a HeNe laser. The light passes through a beam splitter then through two paths. The shorter path being about 0.26 meters, the long one about...
3. ### I Light Refraction, Biconvex Lens, Diagram Help

I've read that the refraction of light at the boundary of a medium can be described as follows: -a line of connected people marching. one side of the line enters mud, and slows down. This causes the non-mud side to pivot towards the slower side, which then causes the line to change direction...
4. ### B What is causing destructive interference in double slit experiment?

When you do the double slit experiment with photons or electrons you get a wave pattern. At certain points no electrons are detected. This is said to be caused by destructive interference. Destructive interference of what? If we shoot single electrons, one at a time, from where is this...
5. ### 3d plot of interference from 2 wave sources with 2d grid surface

Desired output similar to image, but without the objects and with better wave interference: I tried plugging the following into wolfram (I specifically want the values to be adjustable): plot z= H*e^(-m*sqrt((x-a)^2+(y-b)^2))*sin(k*(x-a)+k*(y-b) -w*t) +...
6. ### Engineering How to calculate the interference voltage?

Hello everyone, I have this circuit and I need to determine the interference voltage. I am not sure, where the interference voltage is applied and how to determine it. I think the interference voltage is uv nad my equivalent circuit looks like this: Am I in heading into the right direction...
7. ### A Two Slit Interference Experiment Variations

Examples that have references to special two slit experiments : https://sciencedemonstrations.fas.harvard.edu/presentations/single-photon-interference https://en.wikipedia.org/wiki/Double-slit_experiment If you have an opinion on what you think the experiments tend to support and what they do...
8. ### I Laser and hair - scattering or destructive interference?

There is a video, where the author shows the interference of laser beam on a strand of human’s hair: I bought a laser pointer and reproduced this experiment. Indeed, when a single hair is placed on the way of the laser beam, I see the “scattering” picture (a series of points with intervals of...
9. ### B Does DCQE show a shift between the two "which path" results?

The Delayed Choice Quantum Eraser (DCQE) experiment attempts to show that which-path information can be "erased," and interference recovered. I'll refrain from explaining the experiment, and assume you are familiar with the setup. I refer to the Wikipedia page about it, and the original Kim...
10. ### B Destructive Interference

In this MIT course video, he shows on an optical table that in certain cases, when destructive interference occurs the light is going back to the laser (fast forward to 5:22 in the video below) My question is when I do a double slit experiment with starlight by putting 2 slits in front of my...
11. ### A Question about Stark interference

Hello! I have a question about this paper (@Twigg ?). They claim towards the end of the second page that they use points A and F for their experiment. But for example, at point A the molecular rotation quantum numbers are ##|N=0,m_N=0>## and ##|N=1,m_N=1>##. However, in their experiment the...
12. ### Interference of radio waves

The solution pretends that the ship is a two point source emitter, one h above the water, and one h below the water. The one below the water is out of phase by half a wavelength. I don't understand why then d sin θ = λ - wouldn't it be d sin θ = (1/2)λ since it is out of phase? Thank you.
13. ### I How is an interference pattern changed by an external field?

For example, through the diffracting of electrons and their wave-particle dualistic nature, its possible to produce an interference pattern. And for the resulting electron beam, it will still be affected by the Lorentz force and be deflected by it. At the same time, the position(s) of the...
14. ### Air wedge interference pattern after being filled with water

An air wedge is illuminated with light and an interference pattern is produced. What will happen to the interference pattern when the air wedge is filled with water? The answer given at the back of the book is that the fringe spacing of the interference pattern will increase, however my...
15. ### B Destructive Interference in the sound of multiple firecrackers set off at once?

There is a massive and continuous fireball as fire crackers are exploding, generating thousands of shockwaves. Perhaps they are bouncing off each other and cancelling each other out like noise cancelling headphones,
16. ### I Why do we always see interference pattern in Michelson interferometer?

In a Michelson interferometer with a monochromatic laser, why do we always see an interference pattern even if we move one of the mirrors? Shouldn't it be a certain distance for which the movable mirror reflects the wave to be in opposite phase with the other wave so that they interfere...
17. ### I Constructive interference of harmonic electromagnetic waves

Hello ! I have a doubt as to how is this case, if it occurs, of the constructive interference of two harmonic electromagnetic waves but of different wavelengths or frequencies between them. That is, if between the two electromagnetic waves a new and unique electromagnetic wave is created and...
18. ### Nonreflective film

I thought of sandwiching the coating between lens sufaces and then applied the condition of minimum which gave a thickness of lambda/2*ref. Index and I got totally stuck at the ref. Index.
19. ### I Photon interference and beamforming

In a double slit experiment with one photon sent at a time, the wave function Ψ of the photon reaching the screen is a superposition of Ψ1 (photon going through first slit) and Ψ2 (photon going through second slit). At the screen, Ψ1 and Ψ2 interfere (i.e. the photon interferes with itself)...
20. ### Interference of light in thin films

Phase difference is $\phi=\frac{2pi}{\lambda}* \Delta+\pi$ Phase difference, max: $\Delta \phi=2pim=\frac{2pi}{\lamda_{max}}*2nd$ Phase difference, max: $\Delta \phi=2pim=\frac{2pi}{\lamda_{min}}*2nd+pi$ Flim thickness: $d=100nm$ Set the equations equal to each other i got a d=-100nm which...
21. ### A physics question related to wave interference

However, I do not understand it at all. Since two point sources at A and B are exactly out of phase. The mid point is a node where the amplitude is zero with zero oscillation. How can part (a) be zero? Should that be a quarter of the wavelength away from the mid point?
22. ### Single Slit Interference Pattern: Increased Distance

ATTEMPT AT SOLUTION The effect on the pattern when the screen is moved further away is the bright fringes would become wider, the light intensity of the bright fringes would decrease, and the bright fringes will appear closer together. REASONING I answered this question based on how light...

24. ### I Energy of Electromagnetic Waves in Destructive Interference

Hello ! As we know by definition that: "Constructive interference occurs when the phase difference between the waves is an even multiple of π (180°), whereas destructive interference occurs when the difference is an odd multiple of π." But my question is in the case of destructive...
25. ### Two slit interference: new intensity after doubling width

Here is the solution, I understand how they got E, but I don’t see how they could get E’ from cosine addition formulas? I don’t need to know how to do it with complex numbers.
26. ### I Find the interference function for different emission modes

Homework Statement:: Find the interference function ##I(\delta)## where The emission is analyze by a Michelson interferometer. Relevant Equations:: ##I(\delta) = \frac{1}{2} \int_{-\infty}^{\infty} G(k) r^{ik \delta} dk## ##I(\vec{r}) = I_1 + I_i + 2 \sqrt(I_1 I_i) cos (k\delta)## I have 5...
27. ### A problem involving thin film interference

I know that every time that light goes from traveling through a medium with lower refractive index to one with a higher refractive index the reflected light undergoes a ##\frac{\lambda}{2}## phase change. Since this happens both at the air-plate and plate-glass interfaces we have that the phase...
28. ### I Energy emitted by EM sources under constructive interference

I'm trying to wrap my head around the energy increment under constructive interference. In short, why does energy increase quadratically when each source emit EM wave that interferes constructively? Suppose we have an array of identical and equidistant sources, each of which span the entire x-y...
29. ### I Interference - two waves of different frequencies - beat velocity

Hello, I'm considering the "beats" phenomena. I have two plane waves in some medium with a refractive index n(ω), one propagates in a z direction and second in a direction making an angle θ with z axis. Waves have frequencies ω1, ω2 (not necessarily equal) and k-vectors k1, k2 (not necessarily...
30. ### HW Question regarding double-slit interference

A Homework Question about double-slit interference reads as such: "Finding a Wavelength from an Interference Pattern Suppose you pass light from a He-Ne laser through two slits separated by 0.0100 mm and find that the third bright line on a screen is formed at an angle of 10.95° relative to the...
31. ### Why does a traveling wave pulse get distorted?

I am getting confused by this question. Nevertheless, I tried answering this question. When I see the word pulse, it brings to my mind a pulse traveling in a rope as shown in diagram below and I cannot relate dispersion to the rope medium in which pulse is travelling. What I do know is that...
32. ### A Double double slit experiment and path information

Hi Pfq My question is about this experiment: https://www.nature.com/articles/s41598-020-68181-1 (the link was given by DrChinese. If all the impacts are conserved no interference can be seen on the screens. but if we only take the impacts (Y, yi) where Y is always at the same position on the...
33. ### Questions About Interference Fits

In mechanics, there are several ways of attaching a part to another and what catches my attention the most are the parts that are joined under the pressure fitting. I keep imagining what dimensions and clearances the pieces must have so that they fit together and then don't come apart. Could...
34. ### A Energy problem of light interference

During equal thickness interference, adjust the inclination of the two plates to expand the spacing of interference fringes to 10mm. Then, if a light with a width of 5mm is used for equal thickness interference, whether an interference pattern will be observed, and the width of the interference...
35. ### B What is Destructive Interference?

In an electromagnetic interference pattern with two sources of identically sized waves, the dark areas are where the waves destructively interfere. Being identical in size, the waves should completely cancel one another out, leaving an area empty of any trace of electromagnetism. Yet the area of...
36. ### I Interference of signal photons entangled with idlers

Consider the following experiment: A photon hits a beam splitter, then a non-linear crystal (nichtlinearer Kristall - sorry, prepared the image in German) on each path that does parametric down conversion, splitting the photon into a signal and an idler. The idlers proceed to two detectors (D1...
37. ### 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...
38. ### I Interference and conservation of energy in a resonator

It is known that constructive interference in one place must be compensated for by destructive interference in another. Take a simple Fabry Perot resonator for example. The interference occurring at both sides of the first mirror (assuming one incident electric field) compensate each other out...
39. ### Resultant Frequency and Wavelength of Interfering Sound Waves

##-w1## and ##-w2## are to shift the cosine graph to the right, and ##\frac{2pi}{\lambda}## is to stretch the graph. But I can't seem to draw an appropriate ##y1+y2## graph (quite irregular) and I struggle to find the resultant frequency and wavelength. Also, why is there angular frequency in a...
40. ### Problem involving interference and medium with index n

> A diffraction grating, ruled with 300 lines per mm, is illuminated with a white light source at normal incidence. (ii) Water (of refractive index 1.33) now fills the whole space between the grating and the screen? What is the angular separation, in the first-order spectrum, between the 400 nm...
41. ### I David Deutsch's Many Worlds Interpretation and the Double Slit Experiment

David Deutsch is a well known proponent of the Many Worlds Interpretation. His argument seems to be that a single photon in the double slit experiment must be interfering with one from another world. It is commonly held by physicists that the the photon, as a wave going through double slits, can...
42. ### Interference pattern of a fan of plane waves

So I've kind of made the assumption that there will be an odd number of plane waves and the same amount above and below the z-axis. Then, using the diagram below, I determined the angle the nth plane wave makes with respect to the z-axis to be the angle it makes with respect to the n =1 plane...
43. ### The resultant intensity of two interfering waves

My Try: The resultant field is given by \begin{aligned}\overrightarrow{E}=\overrightarrow{E}_{1}+\overrightarrow{E}_{2}=\widehat{i} E_{0}\cos \omega t+\widehat{j}E_{0}\cos \left( \omega t+\phi \right) \\ \Rightarrow E^{2}=E_{0}^{2}\cos ^{2}\omega t+E_{0}^{2}\cos ^{2}\left( \omega t+\phi...
44. ### B Newton's Rings central spot brightness

How come when the illumination is from below, the central spot is bright, but when the illumination is from above, the central spot is dark?
45. ### I Software for optical simulation with interference

I would like to simulate both double-slit and Mach-Zehnder interference, with some other common optical components such as lenses, beam splitters, mirrors, and wave plates. Is there something online for this or a program that can be downloaded and run on either Linux or Windows? Thanks, Erik
46. ### I Measuring Photon Intrinsic Nature: Is Interference a Factor?

I would like to know, how can we be sure this is not due to the influence/impact/interference of our measurement, not necessarily the intrinsic nature of photons? In most reference books, it seems it is a given and it is not discussed
47. ### B Kim and Scully delayed eraser, interference curve form

Ref https://arxiv.org/abs/quant-ph/9903047. They say the form of their no-which-path-info interference curves (figs 3,4) is "standard". But a standard interference curve has a zero base line. Their base line is a humped curve of the form of their Fig.5, but with about 1/3 of its height. They...
48. ### I Interference Patterns & Photon Paths: Exploring the Double Slit Experiment

Hi. As i understand in double slit experiment photon can arrive at slits through different paths (longer and shorter) and it would still show interference pattern. My question is - if there was some path cutting device in a way of photon (on longest path after length that photon arrive at...
49. ### Calculating Radiation Pattern for a grid of two rows of dipole antennas

Although problem says sketch, what I really want is the formulae by θ for the radiation. After trying this for a while I cheated and looked at the solution. I still can't figure out the steps on how to get to the solution. the answer is: What I tried: I'll assume that the intensity from a...
50. ### Solving Destructive Interference: Angle vs Wavelength

The destructive interference equation for small angles is angle=wavelength/(2a), where a is the width. I assume it means destructive interference since its talking about areas where no light is present. Using the equation after changing degrees into radians I get the answer of 2491 nm when the...