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. N

    What Distance Should the Microphone Move Toward Speaker B for Minimum Intensity?

    Homework Statement Two audio speakers are facing each other, as shown in the picture: https://online-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys214/spring10/hwb/01/05/speakers.gif The speakers emit sound at 1300 Hz; initially the speakers emit in phase (φB = 0). Assume...
  2. P

    Interference at a single wavelength

    Homework Statement I have a question relating to the interference at a single frequency? Does this statement mean that the intereference has occurred between two waves which are completely in phase? I also have a question regarding if two waves which are not in phase but do not cause...
  3. N

    What is the relationship between coherence and interference in wave propagation?

    Hi all From http://en.wikipedia.org/wiki/Interference_%28wave_propagation%29: "Interference usually refers to 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. "...
  4. N

    Why aren't interference filters also polarizers?

    After all, the un-passed light reflects off a transparent medium with a definite index of refraction, right? HELP!
  5. M

    Interference of Light: Where Does the Energy Go?

    Suppose to have a beam of light reflecting over two parallalel surfaces of a material, so that the reflectd rays overlap. There is interference and the square of the amplitude is: r^2 * Eo^2 * sin (2Pi n d / L) where r is the reflection coefficient Eo is the max energy of the field n is the...
  6. S

    Quantum electromagnetic interference

    Hi I wonder if I could get help with some questions that have puzzled me related to the two split experiment and electromagnetic interference in general. I know that if you shine a laser beam through the two split experiment then inference patterns will appear, and that if the path of a...
  7. T

    How Is Film Thickness Calculated from Interference Patterns?

    Homework Statement Light of wavelength \lambda = 500nm, produced by an extended source, is incident at an angle of \phi= 30 degrees from the normal upon a dielectric film of refractive index, n=2, supported on a solid planar substrate. Reflectivity minima are observed to have an angular...
  8. K

    Interference fringes in Young's Double Slit Experiment

    Homework Statement Light of two wavelenghts L1 and L2 (L1,L2 = lambda)creates interference fringes in the Young's double slit experiment. To calculate the least distance from the central maximum where the bright fringes for both L1 and L2 coincide. Given: the distance 'd' between the two...
  9. L

    Constructive Interference of Sound

    Hi, Two speakers, A and B, are located at x = +0.5 m and x = -0.5 m. A 680 Hz signal is sent to both speakers. You then walk around the origin, x = 0, in a circle of radius 5.0 m. v_sound = 340 m/s If you walk once around the complete circle, how many intensity maxima do you hear...
  10. M

    How Can Thin Film Interference Cause Complete Destructive Interference?

    I've learned that when a wave is partially transmitted and partially reflected, it loses some of it's amplitude in order to conserve energy. How then, in thin film interference, can one wave produce complete destructive interference with the other if it has been partially transmitted? Wouldn't...
  11. M

    Why do waves need to be in phase for constructive interference to occur?

    So I know that for constructive interference to occur, in phase waves must be separated by a distance 2 pi. What I'm confused about, though, is what if the point they interfere at is separated by a distance 2 pi, but isn't where their crests meet? Like what if one speaker is one wavelength...
  12. S

    Photon Interference: What Happens to the Photons?

    Hello, could anyone help me with this question? We have a mental experiment consisting in a source S that sends two plane waves of light that propagate in one direction and collide in a photo-detector (PD). It is important to note that the propagation of each wave is in one-dimension, so that...
  13. B

    Interference of rock music at a concert

    Homework Statement Two loudspeakers at an outdoor rock concert are located 2.4 meters apart. You are standing 17.7 meters from one of the speakers and 20.7 from the other. During a sound check, the technician sends the exact same frequency to both speakers while you listen. The technician...
  14. P

    Thin Film Interference and reflection

    Homework Statement What is the thinnest film of a coating with n = 1.43 on glass (n=1.52) for which destructive interference of the red component (660 nm) of an incident white light beam in air can take place by reflection? Homework Equations 2t = m*lambda? The Attempt at a...
  15. M

    Ideal destructive interference of two beams - Where is the energy?

    Two perfectly coherent laser beams point at two different positions on a screen. The energy transmitted by each of the beams is dissipated at the screen - it's either reflected (and thus visible to an observer) or becomes a potential energy of some sort. Now both beams are pointed at a single...
  16. G

    How to Improve the Smoothness of Thin Film Samples?

    1. The problem statement: A wavelength (λ)550 nm light ray traveling thru a viscous medium n1= 1.46 strikes a a crystal n3=1.5 protected by a film n2=1.25. [b]2. Relevant equation: How can I determine the min thickness of the antireflective coating used to minimize the reflection of...
  17. A

    Interference of radia waves

    Homework Statement Radio waves of wavelength 250 meters from a star reach a radio telescope by two separate paths. One is a direct path to the receiver which is situated on the edge of a cliff by the ocean. The second is by reflection off the water. The first minimum of destructive...
  18. C

    Two loudspeakers, an oscillator and constructive interference at a point?

    Homework Statement Two loudspeakers placed X meters apart are driven in phase by an audio oscillator, whose frequency range is 1300 Hz to 1800 Hz. A point P is located A meters from one loudspeaker and B meters from the other. The speed of sound is 344 m/s. What is the frequency produced by...
  19. K

    Lab Prep Help (diffraction and interference)

    Homework Statement This is a second year physics lab on diffraction and interfererence. The theory is not given in the lab manual, and unfortuneately, all of the references they list are unavailable at the library. So, I need some hep recalling a few equation that I am going to need. I am...
  20. V

    Diffraction & Interference: Investigating Wavelengths with Fresnel Biprism

    I'm doing a lab report on diffraction and interference. I've done several diffraction experiments (single slit, double slit, diffraction grating, Fresnel Biprism) to find the wavelength of the laser used. with Fresnel Biprism, wouldn't the refraction within the prism cause a change in...
  21. C

    Is it true photons will not produce an interference pattern in a vacuum?

    "In this study, it is shown with reasons that superposition principle does not work in vacuum. This case can be observed by Young type double slit experiment to be carried out. Since field-field interaction is carried through charged particles, in the absence of charged particles linear...
  22. C

    Exact wave interference distances

    Homework Statement Finding exact distances / angles for some maximum constructive / destructive interference 'bands' for a two-source interference - fixed source-source distance, d - screen parallel with source-source line segment - screen fixed distance away from sources, L - wavelength...
  23. A

    Points of constructive and destructive interference

    Homework Statement Two point sources of sound waves of identical wavelength lambda and amplitude are separated by distance D = 2.0lambda. The sources are in phase. (a) How many points of maximum signal (constructive interference) lie along a large circle around the sources? (b) How many points...
  24. Q

    Single slit diffraction interference

    erm anyone knows why for destructive interference to occur for a fraunhofer's diffraction pattern, the equation is a/2sin(theta) = m(lamda)/2 , ==> sin(theta) = m(lamda)/a ? where a = slit width lamda = wavelength theta = angle the ray makes with the central axis the problem i have...
  25. grooveactiva

    Interference of 3 Cosine Waves: Can They Cancel Out?

    Homework Statement 3 waves are represented by these 3 waves inteferring: cos(Θ-π), cos(Θ+π), 3cos(Θ)? cos(\theta-\pi), cos(\theta+\pi), 3cos(\theta). If I want to diagram these, does the cos(\theta-\pi) and cos(\theta+\pi), cancel each other out? Do I need to convert them to sine...
  26. L

    Finding (1) wavelength, and (2) thickness of film for constructive interference

    1) In a double-slit experiment, two parallel slits are illuminated first by light of wavelength 460nm, and then by light of unknown wavelength. The third-order (m = 3) dark fringe resulting from the known wavelength of light falls in the same place on the screen as the second-order (m = 2)...
  27. W

    Interference between different mode of light

    Hi, If I have two different light modes focused onto a single spot, could they interfere? Thanks
  28. P

    Why do we see 2 waves in interference instead of 3 or 4?

    why do we see 2waves when we consider interference ?why not three or four?eg when we find out conditions formaxima we look for condition when 2 waves interefere...why not 3?
  29. P

    Interference: Resultant intensity.

    Homework Statement To waves with the same frequency interfere. The intensity of the two waves are I1 and I2. Show that the resultant intensity is: I = I1 +I2 + 2*sqrt(I1*I2)*cos(δ) Where δ is the phase difference between the two waves. Hint: Use the relation between intensity and...
  30. C

    Thin Film Interference in a Soap Bubble

    Homework Statement Question: A soap bubble of index of refraction 1.48 strongly reflects both the red and the green components of white light. What film thickness allows this to happen? (In air, the wavelength of red light is 716 nm, of green light 511.429 nm.) n = 1.48 \lambda(r) =...
  31. W

    Wave Interference Angle Calculation

    Homework Statement A two-point source operates at a frequency of 1.0 Hz to produce an interference pattern in a ripple tank. The sources are 2.5 cm apart and the wavelength of the waves is 1.2 cm. Calculate the angles at which the nodal lines in the pattern are far from the sources...
  32. W

    Wave Interference Pattern Question

    A two-point source operates at a frequency of 1.0 Hz to produce an interference pattern in a ripple tank. The sources are 2.5 cm apart and the wavelength of the waves is 1.2 cm. Calculate the angles at which the nodal lines in the pattern are far from the sources. (Assume the angles are...
  33. E

    Could gravitational waves form interference patterns?

    If gravitational waves formed interference patterns, or just simply interfere as normal waves, couldn't that result in gravitational anomalies in absence of mass? Destructive interference could be thought of as negative gravity(dark energy), leading to expansive "forces", whilst constructive...
  34. D

    Sound Interference: Calculating Minimum Distance Between Speakers

    Okay, this may not be more related to soung engineers. But say for example, if there was a concert - an there was a crowd. What formulas and calculations are involved to make sure the the interference of sound is kept to a minimum? As they wouldn't like to have the crowd on the left to have...
  35. A

    Solving Sound Interference: Phase Difference of Waves at 4.40m & 4.00m

    Homework Statement Two sound waves, from different sources with the same frequency, 540 Hz, travel in the same direction at 330m/s. The sources are in phase. What is the phase difference of the waves at a point that is 4.40 m from one source and 4.00 from the other. Homework Equations...
  36. M

    How Does Wavelength Affect Double-Slit Interference Patterns?

    Homework Statement In a double-slit interference experiment, the slits are illuminated with a red laser light at 632 nm. The interference pattern seen on the screen is drawn below: How would I carefully draw, in the same diagram, the pattern that you would see with a blue laser at 450 nm...
  37. P

    Interference wave have solution need explanation

    Homework Statement In Fig. 17-35, sound with a 46.4 cm wavelength travels rightward from a source and through a tube that consists of a straight portion and a half-circle. Part of the sound wave travels through the half-circle and then rejoins the rest of the wave, which goes directly through...
  38. F

    How Does Changing Wavelength Affect Fringe Spacing in a Double-Slit Experiment?

    Homework Statement A double-slit experiment is performed with light of wavelength 600 nm. The bright interference fringes are spaced 1.8 mm apart on the viewing screen. What will the fringe spacing be if the light is changed to a wavelength of 400 nm? Homework Equations Fringe spacing...
  39. K

    Is There a Real Difference Between Diffraction and Interference in Physics?

    I am reading texts on fundamental physics about diffraction and interference. When comes to diffraction, it takes a single slit as example and using Huygen's principle to explain how the wave transmitt and form the pattern. It sounds like that the pattern is due to interference. One textbook...
  40. O

    Interference and Diffraction: Coating on a Lens to Minimize Reflection

    Homework Statement What is the minimum thickness of coating which should be placed on a lens in order to minimize reflection of 661 nm light? The index of refraction of the coating material is 1.40 and the index of the glass is 1.65. Hint: You must take into account the 180 degree...
  41. M

    What is the thickness of the paper in this interference experiment?

    Homework Statement A piece of paper is placed at the end of an air wedge 4 cm long. Interference fringes appear when the light of wavelength 639 nm is reflected from the wedge. A dark fringe occurs at both the vertex of the wedge and at its paper end, and 56 bright fringes appear between...
  42. W

    Single Slit Interference: Explaining the Phenomenon

    Single slit interference. ?? Can someone please explain to me about the single slit interference phenomenon? My teacher said that after passing through the slit, it can be modeled that there are two wave source coming form each end of the "wall" which makes the slit. How can this actually...
  43. A

    Interference in 2D (wavefronts)

    Homework Statement The figure shows the circular wave fronts emitted by two wave sources. Make a table with rows labeled P, Q, and R and columns labeled r1, r2, \Deltar, and C/D. Fill in the table for points P, Q, and R, giving the distances as multiples of \lambda and indicating, with a...
  44. K

    Constructive and destructive wave interference

    EQUATIONS USED I have some conceptual questions about constructive/destructive interference based on the equations: ∆x= nλ ∆x= (n+1/2)λ Where n is any integer MY CONFUSION & EXAMPLE I don’t understand why the condition to get constructive interference is ∆x= nλ, and the condition to...
  45. U

    Interference of two radio waves

    Homework Statement Two coherent sources of radio waves, A and B, are 5.00 meters apart. Each source emits waves with wavelength 6.00 meters. Consider points along the line connecting the two sources. At what distance from source A is there constructive interference between points A and B...
  46. Q_Goest

    Buckyball Interference, classical/quantum border?

    In '99, Markus Arndt published his paper in which single buckyballs (primarily C60 molecules) were fired at a diffraction grating and quantum interference was found. Arndt's experiment used single molecules that had a velocity of roughly 220 meters per second. The molecules traveled roughly 1...
  47. P

    Does Beam Interference Depend on Longitudinal Distance Post-Beamsplitter?

    If you have 2 laser beams, A and B, at right angle with each other, that you send towards a beamsplitter (BS), such that you get 2 output beams from the BS, one being the sum of the reflected part of A and transmitted part of B, and the other the transmitted part of A and reflected part of B...
  48. M

    Interference pattern, wavelength

    Homework Statement Suppose the interference pattern shown in the figure is produced by monochromatic light passing through two slits, with a separation of 127 µm, and onto a screen 1.14 m away. What is the wavelength? Homework Equations wavelength = (dsin\theta) / m y=Ltan\theta...
  49. P

    Thin Film Interference: How does Maxwell's Equations Explain?

    Not really a homework problem. Just wanted to know: When light moves from a medium of lower index of refraction to that of a higher index of refraction, the reflected ray suffers a phase change. (Thin film interference) But the other way round, this doesn't happen. This can be shown by...
  50. G

    Interference Wedge Problem - Analytical Chemistry&Instrumental Analysis

    Homework Statement A 10.00 cm interference wedge is to be build from a dielectric layer n=1.34 and glass plate covers which have a linear dispersion from 400 to 700 nm. a) 1st-order-interference wedge How would be its construction?Indicate its thickness at the two ends of the wedge...
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