# What is Constructive interference: Definition and 48 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.

View More On Wikipedia.org
1. ### I Can a single photon of a single frequency pass through a FP cavity?

I was watching this amazing video about FP cavities and the creator mentioned that a single photon shouldn't pass through that cavity. Only multiple photons can. This doesn't make sense to me. The cavity works thanks to interference and single photons still interfere with themselves, so...
2. ### I Delayed Choice Quantum Eraser with altered beam splitter

Hi People, In Kim's real setup for interference patterns we use a beam splitter as 50:50 (reflectance,transmittance rate), lets assume we use 20:80 (%20 reflectance, %80 transmittance) for beam splitter what could we observe in this situtation on detectors (except D3,D4)? Dont forget we use...
3. ### Derive expressions for the resonant frequencies of these Planar mirror resonators

I was trying to do the exercise from Saleh's book, but I had some doubts. Any tips on how to resolve it? My partial solution for the three-mirror ring: For constructive interference to occur, the total phase accumulated in a round trip must be an integer multiple of 2π. Let's denote the phase...
4. ### I Questions About Bragg's Law of X-Ray Diffraction

Bragg's law is schematically shown on the picture: Two parallel and plane waves are shown which propagate towards the crystal. For plane waves, wave fronts are flat planes perpendicular to the wave propagation with infinite size. In reality, there are no plane waves. Nevertheless, they are...
5. ### 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...
6. ### 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...
7. ### I Constructive Interference of Light

When two photons constructively interfere, what is resultant photon/waves' characteristics? When we talk about physical waves like sound, the constructive interference results in their amplitudes essentially being added together. But with light, my understanding is that the amplitude of a...
8. ### Using constructive interference of audio frequency waves to lower distortion

Hello everybody . I would like to ask you for an opinion. audio waves passing through a horn or waveguide experience a small or relatively large distortion. do you think it is possible to eliminate distortion by making use of constructive interference?
9. ### Find Wavelength of Light Wave for Optimal Constructive Interference

The green ray is moved upwards for clarity, they are all on same x-axis with no y component. Theres a phaseshift at both reflections of the green light because n1 and n3 are > n2. This results in a complete wavelength phaseshift, aka no impact on the wave. That means that only the extra travel...
10. ### Constructive Interference in Coherent Antenna Arrays

Homework Statement A radio transmitting station operating at a frequency f=100 MHz has two identical antennas that radiate in phase (in other words, coherent with respect to each other). Antenna B is 10 m to the right of antenna A. Consider the point P between the antennas, and along the line...
11. A

### Newton's Rings and Thin Film Interference

Homework Statement A total of 31 bright and 31 dark Newton's rings (not counting the dark spot at the center) are observed when 550-nm light falls normally on a planoconvex lens resting on a flat glass surface. How much thicker is the center than the edges? Homework Equations 2t = mλ 2t =...
12. A

### Diffraction Grating and White Light Problem

Homework Statement White light containing wavelengths from 400 nm to 750 nm falls on a grating with 6000 lines/cm. How wide is the first-order spectrum on a screen 2.0 meters away Homework Equations dsinθ=mλ for constructive interference dsinθ=(m+1/2)λ for destructive interference Δx = λL/d...
13. T

### ASOE Physics Exam Q - Diagram for Constructive Interference

1. The problem statement, all variables, and given/known data So I am studying for the ASOE physics test. I came across the following question where I can't really understand the answer to it: The actual answer is: http://prntscr.com/fum35c Could someone help me and explain what they are...
14. ### What are the practical limits of constructive interference?

The "wireless power" thread made me think of this, but I have pondered it before when it comes to microphone arrays etc You can easily find documentation on the interference patterns N in-line sources of waves generate. E.g. The annoying thing here is that you have infinitely extending lobes...
15. ### Thin film constructive interference

Homework Statement Three experiments involving a thin film (in air) sandwiched between two layers of air are shown with nair < nfilm. If t denotes the film thickness and λ denotes the wavelength of the light in the film, which experiments will produce constrictive interference as seen by the...
16. ### Coating Eyeglass Lenses(destructive interference)

Homework Statement Eyeglass lenses can be coated on the inner surfaces to reduce the reflection of stray light to the eye. If the lenses are medium flint glass of refractive index 1.62 and the coating is fluorite of refractive index 1.432, (a) what minimum thickness of film is needed on the...
17. ### Constructive interference with sound -- word problem

Homework Statement [/B] I was little bit confused about interference word problem in an old physics exam. I managed to ace the problem in the exam, by applying a little bit common sense to it, but I feel like I didn't understand the concept of the interference completely. (Loud)speakers A and...
18. ### Light (Constructive/Destructive Interference)

Homework Statement This is not a homework question but I would like if someone could explain to me when to consider what equation constructive/destructive? I learned these two equations very vaguely in class: dsinθ = mλ or d(ym)/L=mλ dsinθ = (m+1/2)λ or d(ym)/L = (m+1/2)λ The power point...
19. ### Question on destructive and constructive interference

Homework Statement Two speakers A and B are 3.50m apart and each one is emitting a frequency of 444Hz. However because of signal delays, speaker A is 1/4 of a period ahead of B. Find all points relative to the centerline between A and B where there is constructive interference. Include angles...
20. ### Which waves can have a constructive interference?

Homework Statement Which waves can have a constructive interference? Homework Equations ∆x=kλ The Attempt at a Solution I think that waves with the same frequency and phase can have a constructive interference. What if they only have the same frequency? Can they create constructive interference?
21. ### Destructive vs Constructive interference

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 694 hz. You are standing between the speakers, along the line connecting them and are at a point of constructive interference...
22. ### 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...
23. ### 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...
24. ### 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...
25. ### 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...
26. ### 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...
27. ### Constructive Interference of Sound Waves

Suppose two loudspeakers are separated by three meters and are being driven by exactly the same sinusoidal signal at a frequency that can be varied. If you are located four meters away directly in front of one of the speakers, determine three lowest frequencies for which you would hear...
28. ### Thinnest film that will give constructive interference for red light

Homework Statement When a thin soap ﬁlm is very thin, we see it as black. How thick (in nm) is the ﬁlm in the region where we see the ﬁrst red band? Take the wavelength of red light to be 752 nm and the index of refraction of the soap to be n = 1.33. Homework Equations [2nt/λ] - 1/2...
29. ### Constructive Interference of Sound waves

Homework Statement A pair of speakers connected to the same signal generator face each other, one at x=0 and the other at x=1.5m. If they are producing a sound frequency of 2000Hz what are the points (position x) of constructive interference between the speakers? Express your answer in...
30. ### Constructive Interference Problem in the Time Domain

Homework Statement Two waves on a string are given by the following functions: Y1 (x,t) = 4cos(20t-x) Y2 (x,t) = -4cos(20t+x) where x is in centimeters. The waves are said to interfere constructively when their superposition |Ys| = |Y1 + Y2| is a maximum and they interfere destructively when...
31. ### Incomplete destructive and constructive interference

Homework Statement What are the values of incomplete destructive and constructive interference? Homework Equations The Attempt at a Solution when the path difference is in between 1 wavelength and 0.5 wavelength, there would be "incomplete" destructive interference. From my...
32. ### Finding Constructive Interference

Homework Statement A college student is at a concert and really wants to hear the music, so she sits between two in-phase loudspeakers, which point toward each other and are 53.2 m apart. The speakers emit sound at a frequency of 459 Hz. At the midpoint between the speakers, there will be...
33. ### Constructive Interference Eq'n

Homework Statement Derive the equation 2t=(n+1/2)(lamba/index of refraction) to show it's the correct eq'n for constructive interference on reflection. Include a diagram. Homework Equations 2t=(n+1/2)(lambda/index of refraction) The Attempt at a Solution I'm not sure how you'd show...
34. ### What Determines the Point of Minimum Loudness in Speaker Interference?

Homework Statement Hillary stands directly in front of speaker S1 and walks straight away (down on the page) from S1 as shown in the diagram. What is the first distance (measured from S1) at which she will hear minimum loudness? Speed of sound is 343 m/s and the frequency of the sound is...
35. ### Constructive interference - energy non-conservation?

Consider two identical optic fibers with deeply subwavelength tips. Let their tips be placed next to each other, at a distance much smaller than the wavelength. Let light of equal intensity come out of them in phase. Then, by the principle of linear superposition, at some distance much bigger...
36. ### 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...
37. ### 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...
38. ### 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)...
39. ### Optical Path Length Difference & Constructive Interference: Normal Incidence

Homework Statement Light falls at normal incidence onto a transparent film on a substrate as shown i. what is the optical path length difference in the case of normal incidence? ii. if nf>no and nf>ns, what is the condition for constructive interference in the case of normal incidence...
40. ### What Happens to Interference Fringes in Water?

The figure (Intro 1 figure attatched ) shows the interference pattern obtained in a double-slit experiment with light of wavelength . PART A Identify the fringe or fringes that result from the interference of two waves whose phases differ by exactly . Enter the letter(s) indicating the...
41. ### Minimum thickness of thin film constructive interference

Homework Statement What is the minimum (non-zero) thickness of a benzene (n = 1.501) thin film that will result in constructive interference when viewed at normal incidence and illuminated with orange light (lamba = 615 nm)? A glass slide (ng = 1.620) supports the thin film answer= 204 nm...
42. ### Constructive Interference: Height Difference Matter?

Just curious...I know that constructive interference occurs when two waves are "in phase" but does this mean that the heights of the waves have to be the same? In other words... can two waves that are in phase with each other constructively interfere if one wave has a higher amplitude than the...
43. ### Constructive Interference Problem with 2 Speakers

Homework Statement You are standing a distance d (1 m) in front of one of two identical speakers, being driven by the same source, that are a distance h (3 m) apart. You walk (starting at y=0) along a line parallel to the line of the two speakers. The speed of sound is 340 m/s and the...
44. ### Transmission through constructive interference

A sheet of glass having an index of refraction of 1.32 is to be coated with a film of material having an index of refraction of 1.46 such that green light with a wavelength of 525 nm (in air) is preferentially transmitted via constructive interference. (a) What is the minimum thickness of the...
45. ### Help w/ constructive interference sound wave intensity

The Problem : The sound wave with intensity 31 mW/m2 interferes constructively with a sound wave that has an intensity of 20 mW/m2. What is the intensity of the superposition of the two. I know that you can add the amplitudes for constructive interference or subtract for destructive...
46. ### Constructive interference of monochromatic light

Homework Statement A source S of monochromatic light and a detector D are both located in air a distance h above a horizontal plane sheet of glass, and are separated by a horizontal distance x. Waves reaching D directly from S interfere with waves that reflect off the glass. The distance x is...
47. ### Wave Problem (constructive interference)

Hey everyone, here's a problem that's been troubling me all day and I really have no idea what else to do: "Speakers A and B are vibrating in phase. They are directly facing each other, are 8.0 m apart, and are each playing a 76.0-Hz tone. The speed of sound is 343 m/s. On the line...
48. ### Constructive Interference In Light

The double-slit experiment seems to show wave interference patterns, the dark strips being the result of destructive interference. My question is about the lighted regions, do they display constructive interference? Is the color of light under constructive interference shifted? I realize we're...