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. X

    Understanding single slit interference

    I was just wondering if anyone was aware of a good explanation or physical cause of single slit interference that doesn't involve the Huygens-Fresnel principle. To me, the principle is not very intuitive, light does not eminate from other light (as far as I know). I think I understand that the...
  2. R

    Double-Slit Interference in Quantum Mechanics

    Hi, there Today, a friend came to me and asked the following questions and they made me confused. If the source is strong, the light has to be considered as wave, and the double-slit interference (DSI) can be interpreted, and the conditions for the DSI is (1) same frequencies, (2) parallel...
  3. R

    Conditions for Double-Slit Interference in Quantum Mechanics

    Hi, there Today, a friend came to me and asked the following questions and they made me confused. If the source is strong, the light has to be considered as wave, and the double-slit interference (DSI) can be interpreted, and the conditions for the DSI is (1) same frequencies, (2) parallel...
  4. T

    Destructive interference - What happens to the energy?

    Hi Everyone This is a question which, in various forms has been asked in various places on the Internet but I have never seen a satisfactory answer. I have therefore decided to try and ask it in a unique way which will start off conventionally to begin with. If I have two side-by-side lasers...
  5. D

    Interference of microwave transmitters of different wavelengths

    This question is about the interference pattern observed when the waves from two microwave transmitters interfere. The first parts of the question involve the wavelengths of microwaves being the same for each transmitter. For the last part the question proposes that the wavelength of one of...
  6. J

    Scattering: destructive interference for large particles

    Can someone maybe explain me(or has a good link to a page where this is explained) why scattering in perpendicular direction is suppressed by destructive interference for large particles. i'm trying to understand mie and rayleigh scattering and don't really get why there is no scattering in...
  7. Maxo

    Single slit interference picture

    I'm wondering something about illustrations of single slit interference. I've seen them being illustrated in different ways. One way is this: and another way is this: But I don't understand how these can show the same thing? In the first picture, we have light rays that are obviously NOT...
  8. B

    Diffraction grating interference

    Hello, I'm having a hard time understanding why diffraction grating spots are narrower than those produced by a double slit set-up. I would really appreciate a conceptual understanding but math works too. Thank you
  9. W

    Quantum interference. Really. Really?

    If leptons can stack up on top of each other and not interfere than how can a single lepton do so in the two split experement?
  10. J

    Optimizing Thin Film Coatings for Minimum Reflection: A Practical Guide

    Homework Statement Optical lenses (n=1.40) in cameras are coated with a thin film of magnesium fluoride (n=1.38) to reduce reflections. What minimum thickness is required to give minimum reflection at a wavelength of 550 nm? Homework Equations 2nt = (lamda)/2 The Attempt at a...
  11. Maxo

    Resulting intensity of interference

    Homework Statement Two speakers with the same power output generate sound waves in 360 degrees direction. Both speakers have the same freuqncy and the distance between the speakers is given. How can we from this calculate the sound intensity at any given point around the speakers...
  12. S

    ANS: Perpendicular bisector of the line joining the two points.

    Homework Statement One speaker is located at the origin and the other is located at (x,y)=(0,3.00m). The speakers emit identical sound waves of wavelength 2.00m which are initially in phase. Where does constructive interference occur? ANS: x=1.50m The Attempt at a Solution...
  13. S

    How Close to Speaker B Must You Be for Destructive Interference at 172 Hz?

    Homework Statement Two loudspeakers, A and B, are driven by the same amplifier and emit sinusoidal waves in phase. The frequency of the waves emitted by each speaker is 172 Hz. You are 8.00 m from speaker A. Take the speed of sound in air to be 344 m/s. What is the closest you can be to...
  14. O

    Antenna spacing and interference

    I have a wifi card for a cisco router that has two antennas spaced about an inch apart. The antennas can pivot so that the distance between the same point on either antenna can change. Since the antennas don't remain a wavelength multiple apart at all points on them, why is it that they don't...
  15. K

    Path differences for constructive and destructive interference

    please,I have exams on Tuesday and I need someone to solve this question for me so that I will pass my exams. Your helps will be kindly appreciated.
  16. Luck0

    How the interference of light changes if there's a lens?

    Suppose we have the Young's experiment with a convergent lens between the slits and the screen. How would the interference fringes change? Sorry about the silly question, but I'm having a hard time with geometrical optics. Thanks!
  17. K

    Adding a 3rd Source to a 2 Source Interference Pattern

    http://imageshack.com/a/img834/5921/7iap.jpg Homework Statement Consider the double slit pattern shown above where the distance between slits is d. Each lettered point is labeled according to ΔD, the difference in distances from the slits to that point. ΔD is expressed in terms of wavelength...
  18. P

    The Double Slit Interference: How does it relate to the definition of coherence?

    I know this is a very trivial concept, so can someone please point out to me where I'm going wrong with this? We use coherent waves to observe an interference pattern, and coherence by definition is the presence of a constant phase difference between two waves. Yet, we see bright and dark...
  19. P

    Coherence - A Must for Interference?

    I can't get my head around the fact that for the interference of two waves to occur, the two sources producing the waves must be coherent (Well, that's what my A level Physics book says). Wouldn't it perhaps be more appropriate to say that coherence is only a necessary condition if an...
  20. Saladsamurai

    Large Diameter Interference Fit: Removal Load

    Hello. I have 2 large diameter cylindrical shells that are "rabbetted" together. I am trying to determine the approximate load required to pull them apart without much success. The parameters are as follows (all length dimensions in inches) and result in a .005" (diametric) interference...
  21. P

    Intensity in double slit interference

    I'm a little confused about a small detail when finding the intensity over the screen, as some notes I'm using happen to calculate the same thing twice, with a slight difference the second time. Each method does the following Call the electric field at any point E so we have...
  22. K

    Physics 3: Images, Interference and Difraction

    So three problems I am stuck on. 1.) You have a converging lens with n=1.5,for a symmetric lens so the two lens have same magnitude, what should the radius of curvature be so the focal length is 10cm. I know 1/f = (n-1)[1/r1-1/r2] so that is 1/0.10m =(1.5-1)[1/r1-1/r2] where I am lost is in the...
  23. K

    Young's double-slit interference?

    Homework Statement In a Young's double-slit experiment, a set of parallel slits with a separation of 0.102 mm is illuminated by light having a wavelength of 580 nm and the interference pattern observed on a screen 4.50 m from the slits. (a) What is the difference in path lengths from the two...
  24. J

    Interference of Sound Waves in a Circular Tube

    1. A sound wave with frequency f = 2300Hz is sent into a circular tube of radius R=160cm through an opening at some point A. A receiver lies at point B, separated from A by an angle α=130°. The speed of sound in air is v=330 m/s. Sound propagates from A to B in both directions along the...
  25. F

    Destructive interference with different path lengths?

    A laser's beam is split and then recombined, and the two path delays are adjusted so there is destructive interference at a detector. Let's also say one of the two paths has a measurable delay over the other. Classically speaking, when the laser is first turned on, the detector would be...
  26. ddd123

    Entanglement and interference effects

    When in a pure state, a particle exhibits interference effects in experiments. Wavefunction collapse alters this pure state: if two particles A and B at the opposite sides of a galaxy are entangled, does it mean that interference experiments done using A vary depending upon whether B has been...
  27. H

    Interference patterns in thin films

    Why the interference patterns are separated when there are many light beams transmit through the film? Thanks!
  28. R

    Comparing Standing Waves, Beats & Interference of Waves

    1)What is the difference between standing waves,beats and normal interference of any 2 waves ? 2)Is beats in sound waves same as interference in light waves ? 3)Why do we represent particle displacement with y and wave motion with x in longitudnal waves in which both particle and wave motion...
  29. A

    Why do we see diffraction effects in radio waves but not in visible light?

    When you shine light on a mirror perpendicularly. Does the reflected beam then not interfere with the incoming one? With my intuition it would, and the interference would oscillate between destructive and constructive interference. But then why don't I see that when I do the experiment?
  30. Saitama

    Interference Problem: Finding Maximum Radiation Intensity

    Homework Statement A system illustrated in the figure consists of two coherent point sources 1 and 2 located in a certain plane so that their dipole moments are oriented at right angles to that plane. The sources are separated by a distance d, the radiation wavelength is equal to ##\lambda##...
  31. A

    Thin Film Interference and wavelength

    Homework Statement Light of wavelength 550 nm in air is normally incident on a glass plate (n=1.5) whose thickness is 1.1 X 10^-5 m. (a) What is the thickness of the glass expressed in terms of the wavelength of light in glass?(b) How many reflected waves will experience the 180 degree phase...
  32. I

    Radio Wave Interference between Two Antennas

    Homework Statement Two antennas located at points A and B are broadcasting radio waves of frequency 99.0 MHz, perfectly in phase with each other. The two antennas are separated by a distance d= 12.40 m. An observer, P, is located on the x axis, a distance x= 58.0 m from antenna A, so that APB...
  33. V

    What interference pattern of double-slit experiment does mean

    I have a doubt about the interference wave pattern of double slit experiment with light beam. does it mean the interference of electromagnetic wave (which tells about the frequency causing color) or Spatial probability wave (which was explained by Max Born). I am not good at math. can someone...
  34. J

    Understanding Interference of Sound Experiment

    Can someone please help explain an experiment which I am struggling to understand. You have a speaker without any of the outer casing (just the small disk part) and secure it onto a clamp stand. You then have two microphones; one above the speaker and one below it which are both the same...
  35. T

    How Do Wave Interference and Velocity Relate in Real-Life Scenarios?

    Homework Statement A beach comber walking along the top of a sea wall notices that the waves reflecting off of the concrete breaker are creating a pattern of interference with the original incoming waves. A few meters from the breaker the waves are at maximum oscillation with a time between...
  36. Dadface

    Classical versus quantum interference.

    The classical physics developed by people such as Fraunhoffer and Fresnel seems to work very well at predicting the results obtained when observing interference and diffraction patterns. Quantum theory seems to work well also and can be used,for example when photons are sent one at a time...
  37. U

    Interference of Xrays from a salt crystal

    Hello, In my textbook(Serway), Constructive interference of two rays hitting the first and the second planes , respectively, of a crystal lattice is derived as 2dsin(Θ)=mλ , where Θ is the angle shown in the picture. My question is: shouldn't the equation be 2dsin(Θ) = (m+1/2 )λ instead...
  38. jaumzaum

    Sound Interference Experiment: Explaining Intensity Increase

    I cannot understand the following: Imagine you have 2 sound sources and build up an interference experiment, where far away from the sources you have a receptor. Imagine you put the receptor at the same distance from the sources. If you turn off one source the receptor will receive a sound...
  39. C

    Constructive and Destructive Interference

    Homework Statement Two speakers are 2m apart. You stand 5m back from the centre of the two speakers, and 2m to the side. The speakers are emitting sound at 700Hz, take the speed of sound to be 341 m/s. Are the waves in constructive or destructive super position? Homework Equations...
  40. S

    Energy conservation in identical destructive interference.

    Here's a thought experiment : Two identical spherical waves exactly 180 degrees out of phase destructively interfere throughout all of space. Is the energy contained in them just lost ?
  41. B

    Why do speakers emit buzzing noises when receiving a text?

    Hello, I have a question or two that I suppose will include the nature of light and how that links to electromagnetism. Sitting at my desk doing some work, listening to music over my speakers, I get a text. But I know I'm about to receive the text before my phone vibrates, because my...
  42. F

    Why do we get an interference pattern in a double slit experiment?

    This is another one of those things that I had always assumed to have a very simple explanation. After all, I've seen so many simulations of waves interfering with each other and forming the distinctive interference pattern, and even watched the patterns emerge in actual water waves. The pattern...
  43. zonde

    Interpretation of photon interference

    I would like to hear comments about interpretation of photon interference in context with Pfleegor-Mandel experiment "Interference of Independent Photon Beams". There is a blog post about this experiment: http://scienceblogs.com/principles/2010/11/19/interference-of-independent-ph/. Original...
  44. S

    Microwaves and Interference problem

    I'm working on my physics prelab, but I can't seem to get this answer. The question states: Measuring the detector´s output as a function of its position along the goniometer (look it up!), we see that there are maxima and minima in the signal. Starting at one of the maxima, we find 6...
  45. G

    Interference of Light - Thin Film

    Homework Statement Plan plates of glass are in contact along one side and held apart by a wire 0.05 mm in diameter, parallel to the edge in contact and 20 cm distant. Using filtered green mercury light (λ = 546 nm), directed normally on the air film between plates, interference fringes are...
  46. V

    SQUID (superconducting quantum interference device)

    Hi all, I am looking to do some magnetic measurements for some research (chemistry...) but I'm hoping to get an understanding of how a SQUID instrument works. I was wonder if anyone could give me a qualitative overview or if anyone know any resources without math-heavy explanations. Thanks!
  47. patrickmoloney

    Destructive interference Problem

    Homework Statement two point sources A and B generate sinusoidal waves in a water surface. The sources are 6.0 cm apart and vibrate in phase with the same amplitude and frequency. Points of destructive interference are observed on AB, the line joining the two sources. the two nearest such...
  48. N

    Moire pattern and interference of plane EM waves

    Homework Statement Look at the Moire pattern in "Oppgave 5" (assignment 5) in the attached pdf file. The Moire pattern you see is supposed to represent the interference between two plane EM waves whose directional ##\vec{k}## vectors form an angle ##\theta## with each other. Anyway, the main...
  49. N

    Interference of two plane waves in any point of space

    Homework Statement For two plane EM waves with identical amplitude, frequency, polarization and phase traveling in the directions of ##\hat{k_1}## and ##\hat{k_2}##, show that their average intensity is given by ##2I_0[1+\cos((\vec{k_2}-\vec{k_1}) \vec{r})]##The Attempt at a Solution Ugh...
  50. P

    Young's double slit interference

    Homework Statement In a young's double slit experiment the slits have the same width and are separated by a distance a. an observation screen is placed at a distance L=1m from the slits at a point on the screen a distance y from the optical axis the optical path difference between the 2 waves...
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