What is Double slit interference: Definition and 49 Discussions

In modern physics, the double-slit experiment is a demonstration that light and matter can display characteristics of both classically defined waves and particles; moreover, it displays the fundamentally probabilistic nature of quantum mechanical phenomena. This type of experiment was first performed, using light, by Thomas Young in 1801, as a demonstration of the wave behavior of light. At that time it was thought that light consisted of either waves or particles. With the beginning of modern physics, about a hundred years later, it was realized that light could in fact show behavior characteristic of both waves and particles. In 1927, Davisson and Germer demonstrated that electrons show the same behavior, which was later extended to atoms and molecules. Thomas Young's experiment with light was part of classical physics long before the development of quantum mechanics and the concept of wave-particle duality. He believed it demonstrated that the wave theory of light was correct, and his experiment is sometimes referred to as Young's experiment or Young's slits.

The experiment belongs to a general class of "double path" experiments, in which a wave is split into two separate waves that later combine into a single wave. Changes in the path-lengths of both waves result in a phase shift, creating an interference pattern. Another version is the Mach–Zehnder interferometer, which splits the beam with a beam splitter.In the basic version of this experiment, a coherent light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate. The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles. However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves); the interference pattern appears via the varying density of these particle hits on the screen. Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave). However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. These results demonstrate the principle of wave–particle duality.Other atomic-scale entities, such as electrons, are found to exhibit the same behavior when fired towards a double slit. Additionally, the detection of individual discrete impacts is observed to be inherently probabilistic, which is inexplicable using classical mechanics.The experiment can be done with entities much larger than electrons and photons, although it becomes more difficult as size increases. The largest entities for which the double-slit experiment has been performed were molecules that each comprised 2000 atoms (whose total mass was 25,000 atomic mass units).The double-slit experiment (and its variations) has become a classic for its clarity in expressing the central puzzles of quantum mechanics. Because it demonstrates the fundamental limitation of the ability of the observer to predict experimental results, Richard Feynman called it "a phenomenon which is impossible […] to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery [of quantum mechanics]."

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  1. elou

    I Why is there no single slit interference when one slit is closed in a double slit experiment?

    When two slits produce an interference pattern, and one slit is closed, then the interference pattern disappears. But one slit interference should still be possible. What should be the measurements of each slit for this to occur? That is, that, starting with a double slit, closing one slit does...
  2. Samina

    B View double slit from other end

    Our eyes not only detect the visible spectrum of light; they can also show the direction the photons are coming from. If, instead of a detecting screen, we use a moving camera or an array of cameras, can't we tell exactly which slit a photon / electron passed through?When viewing a light source...
  3. David Charles

    I Double Slit Interference Question II

    A stream of photons pass through a double-slit. The photon stream emerging from each slit then passes through a crystal which splits each photon into coherent entangled pairs. One photon from each pair heads towards a detector (D0) that "can be scanned by a step motor along its x-axis for the...
  4. David Charles

    I Double Slit Interference Question

    A laser provides a constant stream of photons which pass through a double-slit. The photon stream emerging from each slit then passes through a crystal which splits each photon into coherent entangled pairs. One photon from each pair heads towards a photosensitive screen and the entangled twin...
  5. Y

    What is the Relation Between Distance and Angle in Double Slit Interference?

    Homework Statement question (iii) 2. Homework Equations D=sd/λ (where D is the distance from slit to screen, s is the distance to the central maxima, and d is the slit separation)[/B] The Attempt at a Solution I plugged the values s=0.3*10^(-3), d=4.5*10^(-3) and λ=633*10^(-9), and got the...
  6. S

    Double Slit Wave Interference - what is m?

    Hi, I'm doing a very simple problem, but I don't understand the diagram provided (see image below). What is m here? I know that m is the order with respect to the central bright fringe, but there isn't a central bright fringe (assuming those circles are the bright fringes)? Homework...
  7. Adiater

    I Double-Slit Interference w/ Separate Sources

    If you have two similar coherent sources which are separated from each other by a barrier. Now one source sends particles one by one into one slit and the other sends particles into the other in a double slit interference experiment. Now, the photons are always undistinguishable, so they should...
  8. A

    Intensity for Young’s Double Slit Interference

    Homework Statement Hi The experimental setup involved a helium neon laser of wavelength 670nm +- 1nm, pointed towards a lens with focal length 500mm +- 1mm. (so that the equations used corresponded to the far field diffraction pattern) and onto a photo diode so that for all intents and...
  9. P

    Double slit interference: moving waves

    As I understand the double slit experiment, an interference is created on the barrier. Usually the drawing is made as the constructive waves hit the wall perfectly in middle. Let's say the wave has a frequency f, the interference should be moving away from the middle at time t+f/4. Why we don't...
  10. John Morrell

    I Understanding Double Slit interference and Uncertainty

    I've recently been doing some learning about the double slit experiment and a bit about how, qualitatively, quantum electro dynamics works. Something that I wondered about for a long time was how momentum could be conserved in these systems when we assume that a particle could land in any number...
  11. O

    B Basic question about double slit interferance

    I am new here so I will start with a warming up question :) My question is very trivial here we go: In double slit experiment when shooting one photon at a time, we get interference pattern. Then when we put a sensor at one of the slits the interference pattern disappears because we now know...
  12. CricK0es

    What is the missing variable in the double slit interference pattern?

    Homework Statement Laser light of wavelength 517 nm illuminates two identical slits, producing an interference pattern on a screen 87.5 cm from the slits. The bright bands are 1.15 cm apart, and the third bright bands on either side of the central maximum are missing in the pattern. a.) Find...
  13. tomdodd4598

    I SQM vs Pilot Waves - Potential issue with Pilot Waves?

    Hey there. I'm not a expert in quantum mechanics, although have some experience with it, but I'm certainly far from being an expert when it comes to the pilot wave interpretation. For whatever reason, pilot waves have been mentioned quite a lot recently, and so I decided to take a closer look at...
  14. M

    Solving Double Slit Homework Qs: Phase Difference & Destructive Interference

    Homework Statement Two antennas located at points A and B are broadcasting radio waves of frequency 98.0 MHz, perfectly in phase with each other. The two antennas are separated by a distance d= 6.20 m. An observer, P, is located on the x axis, a distance x= 60.0 m from antenna A, so that APB...
  15. Miguel Velasquez

    When you heat a sheet, does it expand or compress?

    If a sheet containing two very thin slits is heated (without damaging it), what happens to the angular location of the first-order interference minimum? a) It moves toward the centerline. b) It moves away from the centerline. c) It doesn't change.Condition for m-order interference minimum...
  16. 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...
  17. 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...
  18. F

    Double Slit Interference (slit width relevant)

    Hi everyone, So my quantum physics teacher gave this problem to solve as homework: An experiment to watch neutron diffraction was made. The neutron wavelenght measured was 18.45 Angstroms. The double slit was created by putting a thread in the middle of a single slit. The dimensions of the...
  19. 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...
  20. 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...
  21. 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...
  22. PsychonautQQ

    Double slit interference missing maximum problem

    Double slit interference "missing" maximum problem Homework Statement In the double slit interference experiment, d is the distance between the center of the slits and w is the width of each slit. For incident plane waves, an interference maximum is "missing" when what relationship between d...
  23. H

    Double slit interference experiment

    If separate baffle around two different substances,What impact on the interference fringes?
  24. P

    Can double slit interference be explained by the influence of previous photons?

    The usual interpretation of the double slit experiment, when done with a single photon at a time, is that the photon must interfere with itself. However interference cannot be measured in a single-photon experiment - it requires a large number of photons to manifest a discernible interference...
  25. S

    Dual particle and dual double slit interference

    In short the question I am trying to answer is: 1. do the "waves-functions" from separate particle interfere? 2. do the Schrodinger equations predict the interference pattern caused by the interference of the "wave functions" of two separate particles? The above question is...
  26. K

    Double slit interference with single pencil lead?

    Hi guys, Was trying out a home made double slit experiment as I've seen on youtube with a laser pointer and 2 pieces of pencil lead. Then I realized that I can obtain the same interference pattern with the single pencil lead. Is this equivalent to a double slit interference?
  27. L

    Very confused: why is the path difference in double slit interference dsinθ?

    Homework Statement The more I think about path difference, the more confused I get. First of all, HOW DO PEOPLE know that the path difference is dsinθ? Why do we draw a line coming from the first ray that is PERPENDICULAR to the second ray when determining path difference? Please see...
  28. J

    Double Slit Interference Pattern

    I am trying to calculate how wide of a screen you would need in order to observe an interference pattern produced by Young's original real-life double slit experiment. He cut a single narrow slit (width ds) in a window shade, admitting a narrow sliver of sunlight into a dark room. He inserted...
  29. M

    How Do You Calculate Slit Separation in a Double Slit Experiment?

    Homework Statement Red plane waves from a ruby laser (694.3nm) in air pass through two parallel slits in an opaque screen. A fringe pattern forms on a distant wall and we see the fourth bright band 1o above the central axis. (Counting the central bright fringe as zero). Calculate the...
  30. I

    Double Slit Interference Question

    Homework Statement Light of wavelength 680 nm falls on two slits and produces an interference pattern in which thefourth-order fringe is 38 mm from the central fringe on a screen 2.0 m away. What is the separationof the two slits? Homework Equations Sintheta=2m(\lambda2d)...
  31. A

    Variable conditions of double slit interference

    Homework Statement Hi Can anyone help on this. The questions is as follows: In a double slits experiment using red light, a fringe pattern is observed on a screen at a fixed distance from the double slits. How would the finge pattern change if: a) The screen is moved closer to the...
  32. S

    Double slit interference pattern

    Homework Statement Two slits are separated by 0.320 mm. A beam of 500-nm light strikes the slits, producing an interference pattern. Determine the number of maxima observed in the angular range -30 degrees < theta < 30 degrees. Homework Equations d*sin(theta) = m*(lambda) The...
  33. P

    How Does the Central Maximum Shift When a Laser Beam's Angle Changes?

    Homework Statement A laser beam, with a wavelength of 532 nm, is directed exactly perpendicular to a screen having tow narrow slits spaced .15 mm apart. Interference fringes, including a central maximum, are observed on a screen 1.0 m away. The direction of the beam is then slowly rotated...
  34. morrobay

    Double slit interference destroyed by observer or by photons

    When the electron double slit interference pattern is destroyed during measurement detection, to determine which slit the electron passed through, the explanation is that the observation is responsible. Given that detection is done with photons that can interact and alter the path of the...
  35. V

    Alternative Explanation for Double Slit Interference

    i think I have an alternative explanation to the double slit.We can assume that the slit surface is not completely smooth,thus a photon may enter these gaps thus allowing for interference in the case of single photon emitter
  36. L

    Understanding Double Slit Interference: How Do We Count Fringes?

    Homework Statement When they say the first and third bright fringe, do they mean m=1 and m=0..do we count m=0? And likewise for when they say first and third dark fringe, is it m=1.5 and m=3.5? How would we know when to count m=0? Thanks Homework Equations The Attempt at a Solution
  37. R

    Double Slit Interference and linear distance

    Homework Statement In a double-slit interference experiment, the wavelength is 579 nm, the slit separation is 0.12 mm, and the screen is 30.0 cm away from the slits. What is the linear distance between adjacent maxima on the screen? [Hint: Assume the small angle approximation is justified and...
  38. T

    Double Slit Interference (nonzero slit width)

    Homework Statement A mask with 2 slits is illuminated by a light of 589nm wavelength. Slits each have a 0.1mm width separated (centre to centre) by 3.0mm. Calculate the distance between adjacent bright fringes on the screen if a screen is placed 5.0m away from the slits. Homework...
  39. H

    How to Calculate Angle in Double Slit Interference with Given Variables?

    Homework Statement We have the wavelength of 550nm and the distance (d) of 0.120mm. I need to calculate the the angle q. The diffirent parts of this questions corresponds to the diffirent order of n. a) Being n=1 b) n=5 c) n=10 Given variables; Wavelength = 550nm = 550*10^-9m d=0.120mm...
  40. A

    DOUBLE slit interference experiment

    the double slit interference experiment is set up and the fringes are displayed on screen. Then the whole apparatus is immersed in the nearest swimming pool. How does the fringe pattern change?? Which website I can get information?? Thanks.
  41. N

    Understanding Double Slit Interference in Electron Diffraction

    This might sound very basic but... when the electron passes through the two slits and we see the 'pretty' interference pattern on the opposite side what causes the dark fringes to be seen, how does an electron, after acting as a wave and then as an electron when it is recieved, interfere with...
  42. Y

    Find Lambda_2 for Double Slit Interference Pattern

    Homework Statement A laser with wavelength d/8 is shining light on a double slit with slit separation d. This results in an interference pattern on a screen a distance L away from the slits. We wish to shine a second laser, with a different wavelength, through the same slits. What is the...
  43. W

    An Alternative Model of the Double Slit Interference Experiment

    An Alternative Model of the Double Slit Interference Experiment W.H. Madden November 20, 2007 ABSTRACT This post presents an alternative model of the double-slit interference (DSI) experiment. The model is based on a novel physical interpretation of the concept of the DeBroglie...
  44. P

    Diffraction and double slit interference

    hey during proof of expression of double slit interference at a point ,we take into account the interference due to 2 light rays emerging from 2 different slits. here why don't we account for the the interference also due to to light rays emerging from the same slit as in the single slit...
  45. B

    Double Slit Interference Pattern

    It is said that even if we were to send single electrons through a double slit or a single slit we would see an interference pattern on the screen (as long as we don't setup a detector to tell us which path the electron took). How do you send SINGLE electrons into a slit? There are electrons...
  46. D

    Light double slit interference - at home

    Hello Physics Forums Gurus! I am wondering if it would be possible to set up a double slit interference pattern for light at home? Well, I know its possible... but I am just an uneducated student. What kind of dimensions would I need for the slits? I think I would need the light to hit...
  47. G01

    How Does a Thin Glass Affect the Double Slit Interference Pattern?

    Light of wavelength 600nm passes through two slits separated by .2mm and is observed on a screen 1.0m behind the slits. The location of the central max is marked on the screen and labeled y_0 A) at what distance are the m = 1 bright fringes. I got this part. the answer is .003m or 3mm...
  48. A

    What is the maths behind single electron double slit interference please?

    Basically I'm looking to find a mathematical treatment of the single electron double slit interference phenomenom,, presumably someone has already done the maths for it but I can't seem to find it,, can you point me to an article, paper or book which has it? [preferably online] Thanks a lot =)
  49. S

    How Does Tilting the Screen Affect the Double Slit Interference Pattern?

    A vertical screen has two narrow slits separated by distance d. A second screen, parallel to the first, is a distance L away (L>>d) and displays the first minimum of the two slit interference pattern a height h above the horizontal line drawn from the center of the slits to the second...