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. davidbenari

    The Mystery of the Missing Pi Phase Shift in Gaussian Beam Interference

    The superposition of a gaussian beam and a plane wave generates a pattern of rings whose phase shift before and after the focal plane (of the gaussian beam) is ##\pi##. This means that if you measure interference before and after you'll see the minimums and maximums of intensity invert. We can...
  2. I

    Destructive Interference in Water but not Air

    Homework Statement Consider a given monochromatic component of sunlight. The electric field drives a given air molecule. Each oscillating charge of the air molecule radiates waves in all directions, some of which travel to the eye of a given observer. But, for a given molecule (call it No.1)...
  3. Dadface

    I Birgit Dopfer interference experiment

    Hello. I'm interested in the experimental details of the above and have found what I believe to be the original published write up of the experiment. The document is in German and I have managed to get a reasonable understanding of the details mainly from the diagrams and graphs. Translation is...
  4. H

    Finding Maximum Number of Interference Maxima?

    Homework Statement Light of wavelength λ = 535 nm shines through two narrow slits which are 670 μm apart. What is the maximum number of interference maxima which could conceivably be observed (assuming that diffraction minima do not extinguish them and the screen is arbitrarily large)?Your...
  5. vetgirl1990

    Interference vs. diffraction patterns

    Homework Statement The centres of two slits of width a are a distance d apart. If the fourth minimum of the interference pattern occurs at the location of the first minimum of the diffraction pattern for light, the ratio a/d is equal to: ANS: 1/4 Homework Equations Here are the various...
  6. Docscientist

    Can RNA Interference Pathway Help Fight Cancer Gene?

    How exactly does RNAi help in fighting against cancer gene ?
  7. Tazerfish

    Strange Optical Phenomenon (diffraction or something else?)

    First of all i will post a picture of it ... you can find it ... somewhere sorry this is my first post :I I photographed our television with the flash on in order to recreate a strange patter i saw when looking at the suns reflection in the screen.(with my eyes it's not just the camera) You can...
  8. G

    What is the Poynting "vector" mathematically?

    Hi. The Poynting vector is a 3-tuple of real or complex numbers (depending on the respective formulation of electrodynamics) times a unit. It may be pictured as an arrow with some length and direction in IR^3 or IC^3. But is it a "vector" in the strict mathematical sense, i.e. an element of a...
  9. NatFex

    Distance between fringes in an interference pattern?

    For the sake of simplicity let's suppose I'm talking about the diffraction of light through one slit. Are the distances between any two consecutive fringes (apart from the central maximum) exactly equal? Assuming the wavelength, slit width, and distance between slit and screen do not change...
  10. C

    Optics - destructive interference

    Homework Statement White light (most intense at 550nm wevelength) shines on a layer of water (n=1.33) setting on a sheet of plastic film (n=1.25). What minimum thickness of water will produce destructive interference on the surface?[/B]Homework Equations a) phase reversal of light reflecting...
  11. B

    Can Smartphone GPS Units Cause Interference?

    Homework Statement The number of GPS units/receivers on smartphones has increased tremendously. Is this going to cause interference? Why? Homework Equations None The Attempt at a Solution I'm not sure if the units only interfere when they are close to each other or what prevents them from...
  12. R

    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...
  13. LegendLen

    How Do Different Wavelengths Overlap in Double-Slit Interference?

    Homework Statement In a double-slit interference experiment the slit separation is 8.40 x 10-6 m and the slits are 2.80 m from the screen. Each slit has a width of 1.20 x 10-6 m. 2 lights of wavelength 450nm and 600nm are shone on the same slits. If both of the above light sources are shined...
  14. N

    Physics of noise picked up by a radio when home lights are switched off

    I would like to get an, if possible, detailed analysis of the phenomenon by which you hear a noise in your radio speakers when the home lights are switched off. It probably has to do with a wave packet emitted due to switching off the lights, which is picked up by the antenna of a conventional...
  15. entropy1

    B Interference patterns of electrons vs. photons

    I understand that fermions are subject to the Schrödinger equation, but photons are not. I understand that interference patterns of electrons are governed by the Schrödinger equation, but with photons it is different. If I understand correctly, then what is the nature of this difference?
  16. vetgirl1990

    Phase difference between waves in two-slit model

    Homework Statement In a double slit experiment, the distance between the slits is 0.2mm and the distance to the screen is 150cm. What is the phase difference in degrees, between the waves from the two slits arriving at point P, when the angular distance of P is 10 degrees relative to the...
  17. vetgirl1990

    Finding the angle of phase difference - two slit model

    Homework Statement Light of a wavelength 548nm illuminates two slits separated by 0.25mm. At what angle would one find the phase difference between the waves from two slits to be 2 rads? Homework Equations σ / λ = ΔΦ / 2π σ: path difference λ: wavelength Δφ: phase difference The Attempt at a...
  18. vetgirl1990

    How Does Soap Bubble Thickness Affect Light Interference?

    Homework Statement (a) Calculate the minimum thickness of a soap bubble film that results in constructive interference in the reflected light if the film is illuminated with light whose wavelength in free space is λ=600nm. The index of refraction of the soap film is 1.33. (b) What is the film...
  19. R

    Thin Film Interference: Can You Have a Phase Difference>2pi

    If the equation for phase difference, 2(pi)(path difference/wavelength) gave you a value like 12.25pi would that be the phase difference or would it be .25pi?
  20. B

    What is the smallest frequency difference that can be detected by the human ear?

    Homework Statement Consider two sound sources S1 with a frequency of f1 = 3367 Hz and S2 with a frequency of f2 = 3362 Hz. Determine the smallest difference in frequency from 3367 Hz that the average person can detect? Homework Equations The only thing I can think of is approximating the...
  21. S

    What Is the Difference Between Interference and Diffraction?

    I have a confusion regarding interference and diffraction phenomenon, I will be glad if you can post a video or something about interference and diffraction basics. I don't have meaningful concept over their differences. [Mentor's Note: Thread moved to General Physics and thread title edited]
  22. L

    B Delayed choice quantum eraser experiment interference pattern question

    If I understand the delayed choice quantum eraser experiment correctly, it's essentially set up in the manner as the double slit. The only difference is that the detectors are set up in front of the double slits. It was thought that if there was an interference pattern that appeared then that...
  23. K

    Path difference in an interference device

    Homework Statement In a Young’s two-slit experiment a piece of glass with an index of refraction and a thickness is placed in front of the upper slit. (a) Describe qualitatively what happens to the interference pattern. (b) Derive an expression for the intensity of the light at points on a...
  24. SDewan

    Destructive Interference of two waves

    On a single long string, two sinusoidal pulses are started from either end. They have a destructive interference. Both the pulses have kinetic as well as potential energy. Now the point at which they meet, there being a destructive interference, no crest or trough is formed. But right after...
  25. T

    Stuck in wave interference question

    Homework Statement Light of 576 nm wavelength is directed at a two-slit apparatus and produces a famous intensity pattern on a screen 75.0 cm away. Each slit is 0.434 mm wide, and the center-to-center separation of the slits is 0.640 mm. Given that the intensity at the very center of the...
  26. J

    Amplitude at the point of interference

    Homework Statement [/B] Consider 2 radio antennas placed on a 2 dimensional grid at points x1 = (300,0) and x2 = (-300, 0). If the antennas are out of phase such that ϕ2-ϕ1 = π/4 and both are emitting waves of frequency 2.59 MHz. What will the amplitude of the resultant wave be at the point...
  27. Charles Link

    Understanding Non-Linear Optical Interference: The Role of Energy Equations"

    This post is related to a posting I did a couple of days ago, but I will go into more detail on this one, and it should be more easy to see the concept that is presented. A number of years ago, I was explaining interference concepts to a physics Ph.D. who had very little background in...
  28. A

    I Interference pattern in a moving train

    Here is a thought experiment which is a modified version of a one I posted 4 years ago. A moving train, where there are two slits at an equal distance from a photon source along the direction of motion open for a short period of time to allow the entry of photons from the source. The source...
  29. T

    Why does 2slit interference depend on wavelength?

    How do 2 waves in a double slit get cut? I know that light spreads in all directions so, when a double slit is infront of a light source, then it only allows light that goes through the slit past the wall. Why do interference patterns depend on the wavelength? Isnt the wave length perpendicular...
  30. Y

    Emission spectrum will change under possible interference?

    Hi, When a molecule makes a transition from high energy state to low energy state, it emits electromagnetic radiation with a certain wavelength, which can be collected as emission spectrum. However, I have a question right here: For any real case, there are quite a number of molecules in one...
  31. G

    Destructive interference at a surface

    Take two lasers of the same intensity and wavelength and aim them at 30 degrees at the same spot on a mirror, so that at the surface the waves cancel perfectly. What happens? How can the wave be reflected if there is no field present?
  32. Plat

    Radiation or electrical interference? Geiger counter

    First, I hope this is the correct place for this question. I am experimenting with electrical discharges at low pressure, think plasma globe, and I bought a geiger counter to make sure I am not producing x-rays. My vacuum pump is rated down to 5 pascals. The problem is that the geiger counter...
  33. M

    Interference of light Intensity

    An Interference pattern is produced by light of wavelength 490nm from a distant source incident on two identical parallel slits separated by a distance (between centers) of d=0.630mm. a) If the slits were very narrow what would be the angular position theta1 and theta2 of the first and second...
  34. A

    Optics : interference and diffraction

    interference is a superposition of two waves coming two slits... diffraction is a superposition of a family of waves from a single slit.. then how the fringes formed during double slit experiment is actually a superposition of single-slit diffraction from each slit and the double-slit...
  35. R

    Interference from reflection off water across a lake

    #89 chapter 35 A microwave transmitter at height a above the water of a wide lake transmits wavelength lambda to a receiver across the lake height x above the water. Reflected wave interferes with waves arriving directly. Assumptions: width of lake D is much greater than a or x, and lambda is...
  36. M

    Can circularly polarized photons interfere with themselves?

    Hello, I was studying the Bell-state quantum eraser and saw that they placed quarter-wave plates in front of each slit to mark the photons with either clockwise polarization or counterclockwise polarization that were previously either horizontally or vertically polarized. So, now I'm wondering...
  37. naima

    Understanding Interference of Qubits with Varying Density Matrices

    Hi PF I wonder how qubits interfere in interferometers when they are not in pure states. Let us take qubits with density matrix = Id/2. There lay at the center of the Bloch sphere. Half of them can travel unchanged through the left arm. In the other arm they become ##UP_Z##. Then there is...
  38. L

    Two slit diffraction and energy conservation

    Hi all, I have a small misunderstanding about the energy conservation in diffraction from 2 slits. First, I understand the energy conservation of interference from 2 slits. If intensity from each slit is I, then I have intensity of 2I after slits plane. Interference is given by: So at bright...
  39. M

    Is this wave interference? Sound mixing problem.

    This is my first post here, so hello to all. I came here looking for advice. I am far for considering myself even a newbie regarding physics, I have huge gaps in knowledge. However, as I happen to "know my way around computers", I am helping my friend in her art project. Sparing you the...
  40. G

    Destructive Interference of 2 Lasers?

    If I have 2 identical laser pointers, is it possible for me to point them both at the same spot on a wall and see no light at all due to complete destructive interference?
  41. J

    Why don't we see interference in thick films?

    Bear in mind that I am talking about monochromatic light. I looked into this subject and the thing that many say is that when we have thick films, the two reflected waves are not considered to be coherent any more(and something about coherence length). I can't see why this is the case(and I have...
  42. Anton Alice

    Interference requires countable wavefields

    Hello, if have a question concerning the difference between " interference" and "diffraction". Interference can be created, by superposition of countable many wavefields. So if I have a countable amount of wave sources, then the superposition can be called an interference. In contrary, for...
  43. Q

    Constructive/Destructive Interference in a Thin Oil Film

    Hi PhysicsForums, Here's a thin film interference question I'm having problems with. An oil film (n=1.50) floats on a water body (n=1.33) in an air environment. Normal incident white light is reflected by the oil film. But in the spectrum of reflected light, 500nm and 700nm light are missing...
  44. Alettix

    Estimation of data stored on a CD

    Hello! I would be very happy if you could lend me a helping hand with the following problem. :) 1. Homework Statement We know that a CD is read with a laser with a wavelenght of λ = 1 μm. a) Estimate the data stored on the CD. b) We know that the CD contains 80 minutes of sound. How fast is it...
  45. M

    Amplitude of a process + interference term, how what?

    Hello guys, Suppose a process 1+2--->3+4 proceeds thru 3 different intermediate particles and has 3 Feynman diagrams. When we compute the probability then what does the cross terms( interference ) mean? and do we have to always compute the cross terms? What I mean is that when you have 3...
  46. D

    Young's Interference experiment

    I am not sure if this is the correct place to put this question, as it is rather straight forward. But anyway, does anyone know if/where I could find a scanned (or otherwise copied) copy of Young's original experiment (or his paper(s) on it)? I am doing a project, that amounts to some...
  47. DoobleD

    Constant intensity maxima in double-slit interference ?

    Third question about wave optics in two days, hope it's not too much. When we look at the intensity of light on the screen in a double-slit interference experiment (assuming negligible diffraction), we find something like this : When we look at the intensity of light on screen in a...
  48. I

    Diffraction & Interference - interference fringes per cm

    Homework Statement A thin piece of metal foil of thickness 0.0700 mm separates one end of two pieces of optically flat glass. The top sheet of glass is 12.0 cm long. Light of wavelength 529 nm is normally incident on the glass. How many interference fringes are observed per cm in the reflected...
  49. 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...
  50. 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...
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