Diffraction of Light Experiments
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Diffraction of Light Experiments

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Questions and Answers

What primarily determines the diffraction envelope in a double slit experiment?

  • The wavelength of the light used
  • The separation between the slits
  • The width of the slits (correct)
  • The distance to the detector

    • According to Babinet's principle, what can be said about the diffraction patterns produced by a single slit and a thin wire of the same width?

  • Only the wire produces an observable pattern.
  • They produce entirely different patterns.
  • Only the slit produces a diffraction pattern.
  • They produce the same diffraction pattern (correct)

    • In which type of diffraction pattern does a central minima replace the bright central Airy disc?

  • Far field diffraction pattern
  • Single slit diffraction pattern
  • Fresnel diffraction pattern (correct)
  • Double slit diffraction pattern

    • What is the significance of the resolution limit set by diffraction in optical microscopes?

    <p>It prevents overlapping of airy discs of closely spaced points.</p> Signup and view all the answers

    What is one application of measuring the diffraction pattern from a CD?

    <p>To measure the track width on the CD</p> Signup and view all the answers

    What procedure is suggested to achieve a sharp diffraction pattern in a double slit experiment?

    <p>Adjust the distance between the slits and the detector</p> Signup and view all the answers

    Which is NOT a method mentioned for measuring physical properties using diffraction?

    <p>Calculating the speed of light</p> Signup and view all the answers

    What measurement corresponds to the formula $d = \frac{m\lambda}{\sin \theta_m}$ in the context of diffraction?

    <p>Separation between the slits</p> Signup and view all the answers

    What should be done to avoid backlash error when recording the diffraction pattern?

    <p>Turn the circular scale in one direction only.</p> Signup and view all the answers

    In the double slit case, what is required to locate in contrast to the single slit case?

    <p>Maxima</p> Signup and view all the answers

    How many points should ideally be used to cover all five maxima in the current versus position plot?

    <p>40-50 points</p> Signup and view all the answers

    What is the least count calculated from the given data?

    <p>0.001 cm</p> Signup and view all the answers

    Which of the following measurements is NOT directly necessary when recording data during the diffraction experiment?

    <p>Distance between light sources</p> Signup and view all the answers

    What is the formula for calculating micrometer reading?

    <p>Main scale reading + (number of divisions on circular scale x L.C.)</p> Signup and view all the answers

    What should be avoided when handling diffraction slits and other components to ensure safety?

    <p>Touching the inner surface of the diffraction cell.</p> Signup and view all the answers

    When plotting current versus position, which axis should current be shown on?

    <p>Y-axis</p> Signup and view all the answers

    What path difference corresponds to the first minima in a double slit interference pattern?

    <p>$ rac{ ext{λ}}{2}$</p> Signup and view all the answers

    In the intensity pattern derived from superposition, what condition defines the occurrence of the maxima?

    <p>$eta_m = ±m ext{π}$</p> Signup and view all the answers

    What is the relation between the slit width, wavelength, and sine of the angle for determining the position of the minima?

    <p>$d = m rac{ ext{λ}}{ ext{sin} θ_m}$</p> Signup and view all the answers

    What does a path difference of δ = d sin θ = (m + 1/2)λ signify?

    <p>Destructive interference</p> Signup and view all the answers

    Which equation represents the intensity pattern for light from two slits in terms of β?

    <p>$I(θ) = I_0 ext{cos}^2(β)$</p> Signup and view all the answers

    If the phase shift corresponds to even multiples of π, what type of interference occurs?

    <p>Constructive interference</p> Signup and view all the answers

    In a two-slit interference, what physical principle does the superposition of light depend on?

    <p>Path difference and phase shift</p> Signup and view all the answers

    What is the angle at which the central maxima occurs in the interference pattern?

    <p>$0$</p> Signup and view all the answers

    What is the purpose of the experiment described?

    <p>To measure the intensity patterns generated by diffraction/interference of light</p> Signup and view all the answers

    What principle explains the bending of light waves around obstacles?

    <p>Huygen’s principle</p> Signup and view all the answers

    What condition is necessary for forming a Fraunhofer diffraction pattern?

    <p>The distance between the diffracting obstacle and the screen must be large compared to the slit width</p> Signup and view all the answers

    What is an example of a diffracting element in the experiment?

    <p>A double slit</p> Signup and view all the answers

    What does the precision of the position control in the experiment depend on?

    <p>The arrangement of the optical rail</p> Signup and view all the answers

    Which type of diffraction pattern is the focus of this experiment?

    <p>Fraunhofer or far field diffraction pattern</p> Signup and view all the answers

    Why does diffraction occur when light passes through an aperture?

    <p>Light behaves as a wave and bends around obstacles</p> Signup and view all the answers

    Which measurement is crucial for determining slit separation with micro-meter accuracy?

    <p>The distance between the slit and the detector</p> Signup and view all the answers

    Study Notes

    Diffraction of Light

    • A laser beam is passed through a double slit to observe the intensity patterns created by diffraction and interference.
    • The experimental set-up involves a one-meter long optical rail with a laser source, diffracting element, and a photodetector.
    • The locations of the components can be controlled with a precision of mm and micron.

    Theoretical Background

    • Light travels in a straight line, but bending occurs when it's partially obstructed by an opaque screen with an aperture or a knife edge. This phenomenon is known as diffraction.
    • Diffraction can be explained by Huygen's principle: each point on the wavefront acts as a source of spherical waves. These secondary waves interfere on the screen, creating a diffraction pattern.
    • The aperture width (d) should be larger than the wavelength (λ) of the monochromatic light for diffraction to occur.
    • The distance between the diffracting obstacle and the screen (D) plays a role in the type of diffraction pattern observed:
      • Fraunhofer or far field diffraction pattern: D is large compared to the slit width (d).
      • Fresnel or near field diffraction pattern: D is smaller than the slit width (d).
      • This experiment focuses on Fraunhofer patterns.

    Diffraction by a Single Slit

    • The intensity pattern on the screen generated by the interference of waves from a single slit follows the equation: I(θ) = I₀ (sinβ²/β²), where β = (πd / λ)sinθ.
    • Minima occur when βm = ± mπ, where m = 1, 2... This corresponds to angles θ = ± sin⁻¹(mλ / d).
    • The central maxima occurs at θ = 0.
    • Other maxima occur when βm = ± (2m + 1)π / 2, where m = 1, 2... This corresponds to angles θ = ±sin⁻¹[(2m + 1)λ / 2d].
    • The slit width (d) can be calculated using the positions of the maxima: d = mλ / sin θm.
    • The angle θm is experimentally determined by recording ym (the y-position of the minima) and using the relationship tan θm = ym / D.

    Diffraction by a Double Slit

    • Light from a laser source hits two narrow slits, acting as in-phase point sources.
    • Waves from the slits travel different distances to reach the screen, creating a path difference (δ = d sin  = λ).
    • The path difference causes a phase shift between the waves, creating position-dependent interference patterns on the screen.
    • The intensity pattern for double-slit diffraction is described as: 𝐼(𝜃) = 𝐼₀ cos²(πdsinθ / λ)(sinβ²/β²), where β = (πa / λ)sinθ, a being the width of each slit, and d being their separation.
    • The phase shift determines constructive interference (even multiples of π) and destructive interference (odd multiples of π).
    • Maxima occur when d sin  = mλ, and minima occur when d sin  = (m + (1/2))λ.

    Interesting Facts about Diffraction

    • Babinet's principle: the diffraction pattern of a single slit of width d is the same as that of a thin wire of width d. This is because the net electric field at the screen is zero when the slit and wire are superimposed.
    • Fresnel diffraction pattern for a circular aperture shows a central minima in the near field compared to a bright central Airy disc in the far field.
    • Diffraction limits the resolution of optical microscopes to 0.25 microns.

    Applications of Diffraction

    • Determining track width on a CD by analyzing reflected laser light.
    • Measuring the wavelength (λ) of laser light using double-slit width.
    • Measuring the thickness of fine fibers, such as human hair.
    • Measuring the size of red blood cells.

    Experimental Procedure for Double Slit / Single Slit

    • Set up the laser, slit, and detector on the rail to ensure a clear pathway.
    • Adjust the distance between the slit and detector (D) to obtain a sharp pattern.
    • Record the maximum intensity detected when the laser beam is directly incident on the detector.
    • Scan the diffraction pattern by rotating the circular scale.
    • Record current (microA) versus detector position (millimeter) data.

    Data Analysis for Double Slit

    • Plot current versus position. Identify five maxima (one central and two on each side).
    • Calculate the slit separation (d) using the distance between the central maxima and the side maxima.
    • Calculate the average d and its error (standard deviation).

    Safety Instructions

    • Avoid looking directly into the laser beam as it can cause retinal damage.
    • Exercise caution when handling diffraction slits and other components.
    • Do not touch the inner surface of the diffraction cell.
    • Avoid backlash error while moving the micrometer scale on the detector.

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    Laser Diffraction PDF

    Description

    Explore the fascinating effects of light diffraction through double slits in this quiz. The interplay between light waves and obstacles showcases Huygen's principle and the conditions necessary for observing diffraction patterns. Test your understanding of these optical phenomena and experimental setups!

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