What is Interference: Definition and 999 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. gracy

    Constructive interference and destructive interference

    Is he right there? Is there a principle that says "For every constructive interference, there is an equal (but opposite) destructive interference?" Is it impossible for constructive interference to occur without any destructive interference?I don't think so.Because when there is a constructive...
  2. Maged Saeed

    Points of destructive interference of sound waves?

    Homework Statement Two speakers (S1,S2), emitting sound waves of frequency 340Hz and separated by a distance of 3 m, are driven by the same oscillator. A listener starts walking from point A to S2 Along the line that joins A and S2> How many points of destructive interference will be observe...
  3. AdityaDev

    Resonance in String: Understanding Wave Interference According to Book

    according to book "...Let us look at a particular wave crest generated at the left end of the string by a fork. It travels to the right end of the string, is reflected back, and is reflected again at the fork.Now it interferes with the next wave..." doubt: the fork keeps vibrating and keeps...
  4. F

    Interference viewed in the focal plane

    I'm doing a problem where we have plane monochromatic waves incident on finite double slits (each of width a, separation d), and the transmitted light is observed in the focal plane of a lens of focal length f. The position of the lens isn't specified. So I have worked out that the intensity...
  5. grandpa2390

    Do I understand these two formulas on interference?

    Homework Statement This isn't really a question about a specific problem, just about 2 formulas. I am not sure what the difference is when to use the two formulas. I have a hypothesis, but I need it confirmed or corrected. thankyou :) Homework Equations If you have the Halliday and Resnick...
  6. I

    Determining Wave Parameters for Interference Pattern

    Homework Statement Using the two-dimensional wave interference pattern shown and the two equations involving path difference, complete the following: (please see attachment)a)Measure the wavelength of the waves, the distance between the sources, and the path distance from each of the sources...
  7. H

    Planar wave expansion cancelling through interference

    Hello everyone! In a hypothetical 3D space, with no boundaries around, homogeneous normal conditions, what would happen to the advancement of a planar wave front produced at t=0 with 2cycles in length, λ=3.5m, moving with vector speed "c-arrow=1i-arrow" if an identical planar wave of 2cycles in...
  8. P

    Quarter Wave Plates and Interference

    I have a very fundamental question about interference and quarter-wave-plates. My setup contains only few elements: lightsource, QWPs, double slit and some detectors to see the interference pattern. (Detectors are missing from the bottom of the figure.) An important thing is that the two QWPs...
  9. T

    Magnetic Field effect on Radio Waves (Wi-Fi Interference)

    Hello Physics Forum! I'm in desperate need of proof that magnets or magnetic field will not effect the operation or range or wireless access (Wi-Fi). I have 1/2" rare Earth magnets within a metal housing every 5' within the same area as wireless routers and the customer is concerned that it will...
  10. D

    Circular interference from the equation of a hyperbola

    Hi all, I had a question that I can't seem to find an answer too. I was hoping people could point me in the right direction, or let me know if there is an "easy" method. It has to do with the classic example of two stones in water producing constructive and destructive interference...
  11. O

    Can interference occur without the use of single slit?

    I wonder can a sustained interference pattern be obtained in Young double slit experiment if we do not use single slit between source of light and the double slits when one has a monochromatic source in the experiment. Regards
  12. TrickyDicky

    Quantum interference and superposition

    I would like to have a better grasp of the relation between quantum interference and state superposition that are linked in QM. For instance in the photon double-slit experiment the interference pattern is seen as a consequence of the superposition of the wave function(pure state), and when...
  13. V

    Superposition principle and information

    I have a question about, perhaps, GCSE level physics, if not below, which, for some reason, is not explained anywhere I've looked up. Or, at least, I didn't find any explanation. The picture above is supposed to explain the concept of superposition. It depicts a pair of one-dimensional waves...
  14. Nickyvl

    Unexpected white light interference pattern

    Dear fellow Physicists, For my project I wanted to measure the thickness of a glass plate with white light interference. Before being able to measure, I had to setup an interferometer. Unlike with a Laser, with white light it is hard to find the interference pattern since the coherence length...
  15. D

    Second harmonic generation vs interference

    Hello, I have a question about the mathematical expression of interference and second harmonic generation If we have two waves ##E_{1,2}(\Theta ,t) = E_{1,2}e^{j(\omega t + \Theta)} = \frac{1}{2}(E_{1,2}e^{j(\omega t + \Theta)} + c.c. )## According to the Euler's formula. Now - both...
  16. S

    Question re: photon interference

    I have been getting conflicting information so here are my questions, re: 1. Single photon interference 2. Interference between two photons 3. Two-photon interference 1. Some literature says that only single photon/particle interference exists. Can two photons interfere with each other? 2...
  17. P

    Interference of light (perpendicular plains)

    Hi, Apologies if this is a really basic question, but I'm not a physicist by training. I was wondering how two waves of plane-polarised light will interfere if they have equal intensity, are completely in phase, but their planes of oscillation are perpendicular to one another?
  18. T

    Electromagnetic Interference in Cell Phones

    Consider two adjacent people speaking in cell phones. Why the signals don't interfere with one another? Does each phone communicate with a distinct frequency? If so, how?
  19. N

    Interference in Thin Films: Determining SiO2 Layer Thickness Using a Wedge Setup

    Homework Statement In order to decide the thickness of a SiO2 layer(n=1.5) on Si, a wedge is prepared as shown in the picture. A total of 7 DARK fringes was observed, when light of wavelength 589nm shines prependicularly on the wedge. It is known that light reflected from the Si/SiO2 surface...
  20. AdityaDev

    Can a Convex Lens Converge a Tilted Wavefront?

    If I have a parallel beam of light parallel to x-axis, with the speed of light varying from bottom to top. Let it decrease from bottom to top. (To get such a beam one can pass the beam through a glass slab normal to its surface, whose refractive index increases linearly from bottom to top). Now...
  21. S

    Destructive interference and constructive interference

    Two loudspeakers are placed facing each 4.0 m apart. The speakers emit sound in phase with a frequency of 266 Hz. An observer at the center (2.0 m from each speaker along the line joining them) experiences constructive interference. The speed of sound is 343 m/s The lowest frequency at which...
  22. hdp12

    Wave Optics & Two-Slit Interference Explanation

    I have an online homework question and my classmate told me the answer but I would really like someone to explain to me how that answer was determined. I do not understand. Q: Consider the electric field observed at a point O that is far from the two slits, say at a distance r from the midpoint...
  23. M

    Thin film interference reflection

    Homework Statement A coating of n1 = 1.27 material is to be added to n2 = 1.50 glass, in order to make it "irridescent." a) What is the thinnest layer of material which will have a reflection maximum for normal-incidence light at BOTH 400 and 600 nm (vacuum) wavelength? b) This thickness will...
  24. AwesomeTrains

    Exploring Interference of Plane Waves Using the Residue Theorem

    Homework Statement I have to show that the interference of plane waves: f^{(\pm)}(\vec r,t)=\int \frac {d^3k}{(2\pi)^{3/2}}\int \frac {d\omega}{(2\pi)^{1/2}}e^{i(\vec k \cdot \vec r - \omega t)}\tilde f^{(\pm)}(\vec k, \omega) where the amplitudes are given as: \tilde f^{(\pm)}(\vec k...
  25. M

    Interference of Light - Variations in Intensity

    We perceive intensity as the mod square of the electric field of light. As this electric field is varying sinusoidally then should we not see the interference fringes in a double slit diffraction pattern also vary sinusoidally in intensity as a result (albeit very quickly at the frequency of the...
  26. J

    Two slit experiment at home and interference

    Why is it possible to do this experiment at home and still see light as a wave? Isn't there loads of interference? Or does this have to do with wavelength? If you use a laserpen and 3 needles you can basicly do it at home without shielding off anything...
  27. L

    Finding maximum in interference pattern

    Homework Statement In a three-slit system, the first minimum occurs at an angular position of 5.00°. Where is the first maximum? Homework Equations dsinθ = mλ/N The Attempt at a Solution dsin5° = λ dsinX = λ/3 sinX = 3sin5° X = 1.66° I'm not sure if this is the right equation to find the...
  28. M

    4 slit interference, unequal separation

    Hi all I can't find any guidance on this on the internet, so hopefully someone here can help! Basically, I want to work out the intensity profile produced by a multiple slit experiment, with 4 slits. No problem there, but I need the separation between slits to be unequal! I've found mention of...
  29. M

    How many nodal lines for two point sources at 2.5 lamda separation?

    Homework Statement How many nodal lines are created by two point sources emitting at the same wavelength that are separated by a distance equal to 2.5 lamda? Homework Equations My textbook says, "If two coherent sources located a distance d apart emit identical waves of wavelength lamda, then...
  30. K

    Understanding Light Interference: Exploring EM Radiation and Its Effects

    How can light interfere with other light? I thought EM radiation only interacts with charges? Is it because, at your eye, the EM waves are out of phase? So the EM waves don't 'delete' each other, they both exist in superposition with each other, and one EM wave is pushing the electron one way...
  31. W

    Help with two multiple choice questions related to light and interference

    Homework Statement A thin film of glass is in flush contact with a thin film of transparent plastic that has a higher index of refraction than the glass. Monochromatic light of a certain frequency is shown on both sides of this combination, and there is very little light reflected from either...
  32. W

    Thin film / interference question

    Homework Statement Monochromatic laser light is shown through a double-slit apparatus with a slit separation of onto a screen, but no interference pattern is seen because the thin transparent coating (index of refraction n=1.35) on the screen is creating a thin-film destructive interference...
  33. F

    Double Slit Interference (slit width relevant)

    Hi everyone, So my quantum physics teacher gave this problem to solve as homework: An experiment to watch neutron diffraction was made. The neutron wavelenght measured was 18.45 Angstroms. The double slit was created by putting a thread in the middle of a single slit. The dimensions of the...
  34. K

    Wave constructive and/or destructive interference question

    Homework Statement https://portal.utoronto.ca/courses/1/Fall-2014-PHY100H5-F-LEC0101/ppg/quiz%2061016132114/f1q2g1.jpg The figure shows two sets of water waves, created by two sources labeled "A" and "B." The solid half-circles represent wave crests from A, and the dashed half-circles...
  35. L

    Meaning of Single Photon Interference Minima

    In the double slit experiment, when we send out one photon at a time, what does the appearance of minima in our interference pattern mean? When a single photon is fired, I understand (using "understand" very loosely) that the photon will interfere with itself. When this happens, does it still...
  36. A

    Classic Waves Interference Problem with Wedges

    Homework Statement http://i.imgur.com/Mp77mDR.png Homework Equations Path length interference equation. The Attempt at a Solution Why is the answer to (a) a minima? 1. When the light wave hits the top surface of the top glass, a wave will be reflected with phase change of pi. 2. The...
  37. M

    Thin film interference and anti-reflective coating

    Hi, I actually have two questions that are somewhat related so I am including them in one post. I add much more detail about the system then probably necessary because I'd like to see if I have a correct understanding of how the system works in addition to the question itself. Please bear with...
  38. A

    Destructive and Constructive Interference for Sound Speakers

    Homework Statement http://i.imgur.com/FiYb9OE.png Problem b). Looking at the attached document of my teacher, the visual representation of the answer does make sense. Homework Equations 2pi(delta(x1-x2))+delta(phase constant) Basic interference problem in One-Dimension. The Attempt at a...
  39. A

    What are the equations for interference patterns?

    Homework Statement http://puu.sh/bXBvW/361097a50c.png Homework EquationsThe Attempt at a Solution Not sure how to approach[/B]
  40. P

    Measurement of irradiance of 2 beam interference

    Hi, I have an experiment set up to get two beam interference fringes. I would like to know how I could measure the actual amplitude of the irradiance from the experiment. I have with me a power meter and a CMOS camera. How can I go about this? Thank you
  41. J

    Interpreting Young's Light Interference Data: Can You Help Me Clear My Doubts?

    Hello! I have done this experiment and managed to find this data: http://puu.sh/bO8TJ/ac3520ec8b.png Am I right for saying that the position that reaches the value of 5 amps are the central bright and the position 220-ish as the 1st bright order and the position 260-ish as the 2nd bright...
  42. P

    Interference and Diffraction

    Homework Statement Write down the intensity equation for a two-slit interference pattern with diffraction effects included. Indicate which part originates from double-slit interference and which part from single-slit diffraction. What happens when the angle = 0Homework Equations...
  43. M

    What happens to a wave when it encounters interference?

    If I have two waves traveling in opposite directions as shown in the attached image... After 30 seconds what will the waveform look like? Im having real trouble conceptually understanding this! Please help... Many thanks in advance
  44. M

    First order minimum - Wave interference

    Hi :-) I'm currently learning about wave interference and came across two phrases I can't seem to find the meaning of; first order minimum and second order minimum. What do they mean an how are they used? I presume they are for the order of destructive interference or something?
  45. K

    Constructive or destructive interference after a set number of waves?

    Homework Statement Two sources, S1 and S2, send our circular waves that are in phase and of the same frequency. They have the same wavelength (0,5m) and the same amplitude. Will there be a maxima og a minima at the given points: a) S1P = 5.00 m og S2P = 6.50 m? b) S1P = 5.00 m og S2P =...
  46. Dadface

    What happens to light after interference?

    Imagine a beam of light diverging from a source and being incident on a detector. Now imagine a similar set up but with one main difference. The difference is that on its journey to the detector the beam passes through a second beam such that in the overlap region the two beams interfere. Having...
  47. V

    Maximization of wave interference

    I was thinking about which two musical notes, when played together, maximize the absolute value of the area under the curve of the resulting wave within its period while keeping the amplitude to a minimum (ideally the amplitude of the original two sound waves). I guess you could try to maximize...
  48. J

    How Do You Solve Two-Dimensional Wave Interference Problems?

    Homework Statement "Using the two-dimensional wave interference pattern shown and the two equations involving path difference, complete the following. a) i) measure the wavelength of the waves, ii) the distance between sources, and the iii) path distance from each of the sources to the...
  49. E

    Radio Frequency Interference in Cell Phone

    I'm trying to find out what material might best block or limit radio frequency interference (or at least I think that's the problem, as I understand it). I have a phone, the antenna inside the phone is next to a chip that controls a touch button. Whenever the phone boosts the signal to...
  50. F

    How Far Must Point P Be from Speaker A for Constructive Interference at 400 Hz?

    Homework Statement Two speakers A and B, sends out sounds at 400 hz In what distance x between speaker A and the point P is it constructive interference ? http://s716.photobucket.com/user/Pitoraq/media/Fys2121_zps9a68fef2.png.html Homework Equations λ = 2ΔL/(2p-1), v = 340...
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