What is Path difference: Definition and 35 Discussions

In optics, optical path length (OPL) or optical distance is the product of the geometric length of the path followed by light through a given system, and the refractive index of the medium through which it propagates. In many textbooks, it is symbolically written as Λ. A difference in optical path length between two paths is often called the optical path difference (OPD). OPL and OPD are important because they determine the phase of the light and governs interference and diffraction of light as it propagates.

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  1. heroslayer99

    Path difference of microwaves

    I understand the equation (path difference)/wavelength x 2pi = phase difference, but in this case I do not know how changing the distance of H from the source will affect the path difference. In addition to this, does minima refer to 0 amplitude (complete destructive interference) or does minima...
  2. C

    Proof of angle in path difference formula for two slits

    For this I am trying to prove that angle theta between PQ and QO is equal to theta highlighted so that I know I can use theta is the path difference formula. I assume that the rays ##r_1## and ##r_2## are parallel since ##L >> d## My proof gives that the two thetas are equal, however I am...
  3. S

    Finding path difference of EM waves received by radio telecopes

    My attempt: I think ##x## is the path difference so by using trigonometry, I got ##x=d \sin \theta## But my teacher said the answer is ##d \cos \theta## What is my mistake? Thanks Edit: Sorry, I found my mistake. My ##x## is not the path difference
  4. Kharrid

    Two Speaker Destructive Interference

    I already have the solution in front of me, I am wondering why there is a difference in the formula for path difference. I've attached the problem as well to show the Figure. What I am struggling to grasp is why the path difference for the angles closer to A is dsin(Θ) = (m+1/4)λ while the path...
  5. Jeremy Feng

    Young's Modulus Experiment With a Glass Screen

    Homework Statement Homework Equations Path difference is nλ at maxima, (n+0.5)λ at minima The Attempt at a Solution I think the phase difference between S1 and S2 is not 0 anymore, because the wave effectively takes a longer distance by going through S2. Thus, there is no longer a central...
  6. Ajaroy

    How to calculate the path difference in this question

    1. Homework Statement Two speakers S1 and S2 derived by the same amplifier and placed at y=1 and y = - 1.The speakers vibrate in phase at 600 Hz. A man stands on the x-axis at a very large distance from the origin and starts moving parallel to the Y - axis. The speed of sound in air is 330ms-1...
  7. Theudius

    B Wavelength, Path Difference, Phase Difference

    Hi, would it be possible to explain to me how does wave length, phase difference and path difference all link as I'm struggling with calculations involving these three things.
  8. S

    Why is Newton's Ring Dark in the Center? Exploring Path Difference Theory

    Why the center of Newton's ring is dark? though I am thinking the path difference in the center is zero between two reflected rays... so,I will be glad if you give the correct information about that...
  9. 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...
  10. Gigi777

    Why does diffracted white light have a white central fringe?

    Hey everybody, Homework Statement : [/B] I came across a question discussing Young's Double Slit interference and was wondering how come when we diffract white light through the slits it gives us a central antinodal fringe that is also white? The question itself came in parts firstly...
  11. 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...
  12. toforfiltum

    Path difference between the waves

    Homework Statement Homework EquationsThe Attempt at a Solution I formed a right angle triangle between the arrow downwards,d, and perpendicular line x from arrow. As such, sin θ = x/d. x= d sinθ path difference: d sinθ/λ My answer is C, but answer is B. Where did cos θ come from?
  13. S

    Michelson Interferometer (Zero Path Difference)

    Homework Statement A Michelson interferometer is illuminated with a laser with a wavelength of 514.5nm. A Haidinger fringe pattern is photographed with a lens of focal length 55mm. The diameter of the two adjacent circular fringes in the image are 1.53mm and 2.62mm. How far would the mirror...
  14. S

    Haidinger fringe (interferometer at zero path difference)

    Homework Statement A Michelson interferometer is illuminated with a laser with a wavelength of 514.5nm. A Haidinger fringe pattern is photographed with a lens of focal length 55mm. The diameter of the two adjacent circular fringes in the image are 1.53mm and 2.62mm. How far would the mirror...
  15. D

    Optical path difference of air wedge

    Homework Statement i can't understand why the optical path diffrence is 2nt+0.5λ. why is it so? the 0.5λ is due to the path difference change of 180 degree of when it is reflected lower ray when it is reflected from the lower glass surface... why there's also phase change of 2nt. since both...
  16. L

    Derivation of the Laue Equation -- Problem with path difference

    Hi everyone Homework Statement I'm trying to understand the Laue equation but I have problems unterstanding the derivation, especially one part in my textbook about the path difference (see attachment) The Attempt at a Solution My textbook says that the path difference here is...
  17. D

    Optical path difference caused by double slit

    Homework Statement In this question, when S2 is covered with a very thin glass, the fringe move toward Y . why is it so? Homework Equations The Attempt at a Solution
  18. M

    Understanding Optical Path Difference in Optics | OPD Explained

    SOme one help me with the OPD. How is here the OPD=n2(AB + BC) -n1(AD)? I am not confused with the introduction of 'n'..Rather the path length is confusing me..Why is there a negative sign?
  19. I

    Tricky Path Difference Problem in waves, help (attachment)

    Tricky Path Difference Problem in waves, help! (attachment) Homework Statement check the attachment Homework Equations none needed for part (d) The Attempt at a Solution the first three questions of part (c) i got them out. answers were (c) (i) 2x10 ^8 ms–1 (ii)...
  20. G

    Path difference in Fibre Optics

    Hi, This is a question from a homework which has stumped me: Light is traveling along a fibre optic cable of refractive index 1.52, the refractive index of the cladding is 1.51 and the critical angle between the two is 82. a) what is the most direct route for light along the fibre-optic cable...
  21. I

    What is the Path Difference: Waves

    Homework Statement Two in-phase speakers 4.50 m apart in a plane are emitting 1690 Hz sound waves into a room where the speed of sound is 343 m/s. Consider a point that is 8.50 m in front of one of the speakers, perpendicular to the plane of the speakers. What is the path difference (in...
  22. 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...
  23. M

    Phase difference and path difference

    Hello, What are phase difference and path difference? Can you give me a simple explanation so that I could imagine It would be great if there are some illustrations Thanks
  24. L

    Path Difference: Why a Cold Spot Forms at S

    I was doing a past paper earlier and i got a question about cold spots in microwaves and i needed to calculate path difference the question was: ---------|------->S<---------|--------- Explain why a cold spot is formed at S 18cm | 6cm. 12cm | 30cm The question showed the...
  25. M

    Sound Problem involving a path difference

    Attached is the problem and solution for part B, can someone please explain how they obtain the equation for part B, i don't see why they take the root. Thank you. Homework Statement [PLAIN]http://img153.imageshack.us/img153/8149/97578282.jpg
  26. C

    Determining Path Length in a Double Slit Experiment

    In a double slit, when the distance between the screen is NOT small (i.e. the rays r1 and r2 are not parallel) how is path length determined? Thanks
  27. I

    What is the 'path difference' in waves

    My textbook states that: "Points P₁ and P₂ are both on antinodal lines. The length of the path traveled by wave 1 from its source (S₁) to point P₁ is two wavelengths. The length of the path traveled by wave 2 from its source (S₂) to point P₁ is three wavelengths. The path difference (pd) is...
  28. P

    What happens if the path difference is not a multiple of lambda?

    take it as em waves. if the path difference is nlambda, where n is an integer, the interference will be a constructive one. if the difference is (n+1/2)lambda, it'll be distructive. what's it if the difference is neither nlambda nor (n+1/2)lambda? thanks.
  29. S

    Understanding Path Difference in Convex Lenses

    Path Difference in Lenses... A convex lens will converge all rays parallel to the optical axis to the focus. Now obviously different rays at different distances from the optical axis will travel different distances in reaching the focus. So why does this not create any path difference between...
  30. H

    Path difference in Fabry-Perot etalon

    Hi I'm trying to understand how the Fabry-Perot etalon works for an experiment regarding the Zeeman effect. Looking at the image could anyone tell me why the path difference in the etalon is \Delta l = 2t \cos{\theta}? In my head, the path difference is \Delta l = 2t/\cos{\theta}, in other...
  31. W

    Destructive Interference and path difference

    Hi! I hope I'm posting in the right place! In the destructive interference of waves and solving for the path difference, I"m confused at when we should use m+1/2 vs. m-1/2 ( so the eq'n is PD=(m+1/2)lambda or PD=(m-1/2) lambda Any insight would be greatly appreciated! :) thanks!
  32. L

    Difference between phase difference and path difference

    respected members, could anyone explain the difference between path difference and phase difference ? what does the term phase exactly mean? thanks in advance
  33. K

    Phase shift from path difference

    1. Homework Statement A wave front moving horizontally encounters a block of glass that has an index of refraction of 1.50 in its upper half and an index of refraction of 1.25 in its lower half. The wavelength of the wave front in air is 700 nm. At what lengths would the glass block cause...
  34. K

    Phase shifted waves due to path difference

    Homework Statement A wave front moving horizontally encounters a block of glass that has an index of refraction of 1.50 in its upper half and an index of refraction of 1.25 in its lower half. The wavelength of the wave front in air is 700 nm. At what lengths would the glass block cause...
  35. F

    Path difference and phase difference.

    Pardon the pun, but what's the difference between path difference and phase difference (when talking about interfering light waves)?
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