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. DoobleD

    'Diffraction' or 'Interference' gratings ?

    I recently learned about the so called "diffraction" grating. In most textbooks I have seen, it is described as multiple slits setup, with really narrow slits. It is sometimes said that the width of the slits is much less than the wavelength of the light going through it. Where is the...
  2. DoobleD

    2 slits : diffraction always "enveloppe" of interference ?

    In the double-slit diffraction experiment, two interferences are observed simultaneously : diffraction interference from each single-slit, and double-slit interference (where in the double-slit interference, diffraction is ignored because we considered theoretical slits way smaller than...
  3. B

    How Is the Longest Wavelength of Light Determined for Anti-Reflective Coatings?

    Homework Statement A sheet of glass (nglass = 1.5) is coated with a 95.6-nm-thick layer of magnesium fluoride (ncoating = 1.38) to prevent reflection in the visible spectrum. Assume the incoming light is normal to the surface. What is the longest wavelength of light strongly reflected from this...
  4. I

    How Can I Correctly Calculate the Intensity in a Diffraction Pattern?

    Homework Statement Monochromatic light of wavelength 463 nm from a distant source passes through a slit that is 0.0350 mm wide. In the resulting diffraction pattern, the intensity at the center of the central maximum (θ = 0∘) is 9.20*10-5W/m2 . What is the intensity at a point on the screen...
  5. I

    Interference - Single slit diffraction

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Hi guys, I have a question here which I'm struggling to do and perhaps you could help ; Monochromatic electromagnetic radiation with wavelength λ from a distant source passes through a slit. The...
  6. pratikaman

    What are localised and non localised fringes?

    what does it mean by localisation of fringes?
  7. J

    Why Does Light Interference Differ from Sound Interference?

    Homework Statement Homework Equations I α A2 The Attempt at a Solution My teacher told us that if the source is a light source, then the answer would be B, why? Why would the intensity be the same for each maxima? And zero intensity when at minima? I thought its amplitude will decrease as it...
  8. A

    How many peaks in the interference pattern?

    Homework Statement In a diffraction experiment in which electrons of kinetic energy 110 eV are scattered from a crystal, a first maximum in the intensity of the scattered electrons occurs at an angle θ=10.7 a) How many peaks will there be in the interference pattern? b) What is the spacing...
  9. 24forChromium

    Destructive interference and energy

    Where do the energy go in a pair of photons that are annihilating each other exactly? What happens when they collide with something that absorbs photons like an electron? (I think electron can absorb the e. in a photon to jump into a higher level) Would this light wave become undetectable like...
  10. F

    A Thought Experiment: Photons Passing through Detectors

    Pretend we have a multi-slitted grating whose slits are infinitesimally small. We On each slit is a detector. If we shine (UPDATE) light monochromatic light through the grating, what distribution pattern occurs on the screen past the grating? I understand the train of thought to a slight...
  11. Jimbob999

    Calculating Thin Film Thickness Using Interference Patterns

    Homework Statement A thin film with an index of refraction of 1.60 is placed in one of the beams of a Michelson interferometer. If this causes a shift of 8 bright fringes in the pattern produced by light of wavelength 580 nm, what is the thickness of the film?1.5 µm 2.9 µm 3.9 µm 7.7 µm 16...
  12. S

    What is the trough in destructive interference of EM?

    My textbook says that the trough of the electromagnetic wave cancels out when it meets a crest. Okay, that makes sense, but if the crest is the actual photon/wave of energy, what is this trough that can cancel out the energy? It seems to mean that there are "negative energy photons" in between...
  13. R

    EM Wave Interference: What Happens to Energy?

    When EM waves interfere, what happens to the energy?
  14. C

    Solving an Optics Exam Problem: Interference Fringes

    So, I'm about to take an Optics exam, and while I can easily do most of the last years' exam problems, there are some which I cannot solve for different reasons (perhaps some gross oversight?). Yesterday I stumbled upon this: 1. Homework Statement (my own translation from Catalan) We have a...
  15. thalassa

    Is there constructive or destructive interference?

    Homework Statement Two sound sources are coherent and in phase. Is there constructive or destructive interference at the midpoint between the speakers? Homework Equations Generally, there is constructive interference whenever the path-length difference is an integer times the wavelength...
  16. ElegantSir

    How Do You Calculate Frequency from Wave Loops and Travel Time?

    A string has one end tied to a wave generator, and the other tied to a fixed position,. It takes the wave 0.10 seconds to travel 4.5m. Withing the same distance there are 3 complete loops. Find the frequency of the source. Pretty generic question. But I keep getting stuck at trying to find the...
  17. N

    No interference pattern in double slit when there is a lens?

    Why does the interference pattern of the photon go away when one places a convex lens far away from the two slit to only show a particle build up of the two slits? This is the experimental set up, the lens is in place far after the photons pass through the two slit and hit the back wall in a...
  18. N

    Observed interference in afshar's double slit experiment?

    In afshar's experiment, it shows that the single photon goes through only one of the slits and produces an interference pattern. How is this possible? In this experiment, do we really know which slit the photon went through?
  19. stevendaryl

    B Single-source and multi-source interference

    [Mentor's note: This thread was split out from another longer one because it is an interesting topic in its own right] Something that I've been confused about when it comes to interference between photons is the distinction between two different quantities that can interfere constructively or...
  20. Feeble Wonk

    Macroscopic observation of interference?

    I suppose a related question is in regard to the fundamental nature of quantum superposition. Does any system in superposition "necessarily" demonstrate interference on a macroscopic scale?
  21. andrewkirk

    Polarisation destroying interference pattern for double slit

    I have been trying to mathematically explain the empirical result that putting orthogonal polarisers (quarter-wave plates) behind the two slits of a double-slit setup will erase the interference pattern. The trouble is, my analysis predicts an interference pattern. I must have made a silly...
  22. toforfiltum

    Confused about interference pattern of waves

    Homework Statement Homework Equations dsinθ =nλ The Attempt at a Solution I don't understand why an interference pattern will only be observed along XY only. Why don't the waves intersect along RS. Does it have something to do with R being the midpoint of PQ?
  23. C

    MHB Calculating Travel Time for Light in an Optical Fiber

    Figure 35-57 shows an optical fiber in which a central plastic core of index of refraction n1  1.58 is surrounded by a plastic sheath of index of refraction n2  1.53. Light can travel along different paths within the central core, leading to different travel times through the fiber.This causes...
  24. A

    MHB Interference in a Double-Slit Experiment

    In a double-slit experiment, the distance between slits is 5.0mm and the slits are 1.0m from the screen. Two interference patterns can be seen on the screen: one due to light of wavelength 480nm, and the other due to light of wavelength 600nm. What is the separation on the screen between the...
  25. E

    How does coding affect signal interference in digital communication systems?

    Hello all, The following question is related to digital communication systems. I am studying two systems operating at the same time and on the same frequency. Each system consists of one transmitter and one receiver. However, one of them, let us say system 1, is using channel coding with code...
  26. D

    Double slit interference from antenna

    Consider the situation where the electrons in an antenna accelerate from the top of the antenna to the bottom of the antenna once, what would the interference pattern look like if the electromagnetic radiation from the antenna were passed through a double slit apparatus of an appropriate size? I...
  27. R

    What kind of fringe is seen at the left edges of the slides?

    Homework Statement One microscope slide is placed on top of another with their left edges in contact and a human hair under the right edge of the upper slide. As a result, a wedge of air exists between the slides. An interference pattern results when monochromatic light is incident on the...
  28. D

    Interference pattern for thin films

    Homework Statement A parallel beam of light of wavelength ##\lambda## is incident normally on a thin polymer film with air on both sides. If the film has a refractive index ##n>1##, then, for what value of the thickness, can second order bright fringes be observed in reflection? Homework...
  29. S

    The interference of light and diffraction

    Homework Statement https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xft1/v/t1.0-9/11161364_10206082495958864_2429387894279713850_n.jpg?oh=40982e4e4e7647918991060b6f630acc&oe=55C1808A&__gda__=1439347320_8abd4b5ce66baee04bbc345aef15ec68 In terms of the wavelength of the light λ, what is the...
  30. lulzury

    Small Angle Approximation in Single Slit Interference

    Homework Statement A monochromatic light source is used with a double slit to create an interference pattern on a screen that is 2.00 meters away. If the 2nd bright spot is observed 8.73 mm above the central maximum, can the small angle approximation be used? Show and/or explain your reasoning...
  31. W

    Sound Interference on a speaker

    I had a physics course a few years back that touched on constructive and destructive waves and only today did i notice this phenomenon with my speakers. I was curious about the theory behind this particular scenario in my room. I have one of those mobile speakers, a bose soundlink II. It has 4...
  32. S

    Interference on paper, ground glass etc. surfaces

    With laser pointers being so ubiquitous, everyone is familiar with the sight of interference patterns on paper, ground glass and other surfaces (not to mention more subtle experiments like this one): Quantum Eraser -- which has been discussed recently in other threads. We take it for granted...
  33. E

    Sound Intensity on a Field (no interference)

    Homework Statement Two loudspeakers on elevated platforms are at opposite ends of a field. Each broadcasts equally in all directions. At the halfway point, the intensity is 74.1dB. What is the sound intensity level at a point one-quarter of the way from one speaker to the other along the line...
  34. carllacan

    Interference of circularly polarized waves

    Homework Statement Two (left) circularly polarized monochromatic plane waves S2 and S3 arrive at the xy plane with an incidence angle θ (see figure). Find the intensity of the light projected in the xy plane. (Nevermind S1, it is only mentioned in another part of the problem) Homework...
  35. A

    AH physics exam tomorrow - help with waves question? thanks

    1. Homework Statement If the optical path diff between two light waves is lambda/2 will they always interfere destructively? if this in true then wherever one wave undergoes aphase change of pi at one surface and the second wave does not then these two will always interfere destructively...
  36. A

    Help with interference question AH physics? exam tomorrow :(

    Could someone please explain this question to me I'll include what I thought the answer was and the actual SQA answers. Please can you read my answer just to see what I'm doing wrong and what I don't understand It's from the 2009 past paper AH physics Thanks so much I really appreciate any...
  37. R

    MRI Electromagnet Interference in a Figure-8 cable

    The prevailing wisdom is that coiling excess signal cable under an MRI magnet for storage in a figure-8 configuration will reduce or eliminate induced noise onto the cable from the pulsing fields from gradient coils. I am starting to doubt this, however. A quick diagram of a figure-8 looped...
  38. S

    What is the Wavelength of Light Used in a Double-Slit Interference Experiment?

    Upon using Thomas Young's double-slit experiment to obtain measurements, the following data were obtained. Use the data to determine the wavelength of light being used to create the interference pattern. Do this in three different ways. - The angle to the eighth maximum is 1.12 deg. - The...
  39. Z

    Destructive interference Sound question

    Homework Statement A student enters Best Buy prepared to buy a pair of speakers. Before he does so, he conducts an experiment with them. He places the speakers 4.0 m apart and connects a signal generator to both speakers that produces a single and consistent tone. (constant wavelength and...
  40. W

    Solar cell interference filter

    Homework Statement See attached image, assignment a) Homework EquationsThe Attempt at a Solution Using ordinary trigonometry, I got simply $$\Delta = sin(\theta_i) 2 d tan(\theta_t) n_{air} - 2n_{oxide} d/cos(\theta_t)$$. However, even if I apply Snell's law, it's not the answer I'm supposed to...
  41. W

    Constructive interference and energy conservation

    Hi. Let's say two monochromatic laser beams superimpose in a single point in space in such a way that there's constructive interference. Because there's constructive interference there, the total intensity at that point will be larger than the sum of the separate intensities. Will this mean...
  42. Jilang

    How is quantum interference achieved with atoms fired from opposite directions?

    I came across this today, but wasn't quite sure how it worked. http://www.sciencedaily.com/releases/2015/04/150409081436.htm Are the two atoms fired from opposite directions?
  43. Sab95

    Confusion regarding Interference of light

    I have been reading optics for the past few months. If light has the property of interference, when I look around, why don't I see any interference patterns. does it mean all the waves around me are in phase ? Another question is, why don't Cellphone signals interfere with each other ? they are...
  44. Jilang

    Is polarised light a result of destructive interference?

    This question is prompted by a recent discussion I have been following regarding the insertion of a 45 degree angle polariser between two polarisers at 90 degrees to each other. The insertion of the filter seems to restore missing components which would suggest that those components were present...
  45. L

    Debug help: optical laser interference setup fails to work

    I’m looking to demonstrate destructive optical interference using a laser pointer. I’m splitting the beam with a prism and projecting the beams onto one point on the wall. Somehow I’m failing to get any effect, however. Setup: 1. I’m using a static laser pointer, a prism and a handheld mirror...
  46. M

    Interference-based Rotation Sensing: Utilizing Split Beams and Phase Changes

    What is the production when two beams interference? 2 beams meet, and is there only one left after interference? Like vector.
  47. julianwitkowski

    How to Calculate Wavelength in a Two-Dimensional Wave Interference Pattern

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

    Wave Interference - Calculate Possible Frequencies | Best Buy

    Homework Statement A student enters Best Buy prepared to buy a pair of speakers. Before he does so, he conducts an experiment with them. He places the speakers 4.0 m apart and connects a signal generator to both speakers that produces a single and consistent tone. (constant wavelength and...
  49. C

    Worst frequency for EM interference?

    So I have some big speaker amplifiers at home, and they sometimes pick up radio interference from the CB enthusiast next door (he uses AM, so I'm guessing this is inducing a signal inside my amplifier which amplifies it into my speakers). It isn't really a big problem so I'm not looking for a...
  50. C

    Bragg law vs interference equaiton

    The condition for constructive interference is: n*lambda=d*sin(alpha) Bragg's law is n*lambda=2d*sin(alpha) The diffraction from a crystal cell will also create an interference pattern, so why do these equations differ?
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