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Homework Help: Finding the theoretical value of the wavelength for a double slit experiment?

  1. Nov 1, 2014 #1
    1. The problem statement, all variables and given/known data
    m=maximum h=distance on the screen from the center of the pattern to the mth maximum D=distance from the central bright peak to the slits d=distance between two slits
    I have m=1 d(mm)=0.25mm D=2000mm h=0.5mm wavelength= 6.25E-5mm

    2. Relevant equations
    So I used this equation to find the experimental wavelength for the first 5 wavelengths
    Wavelength= dh/mD for experimental wavelength

    3. The attempt at a solution
    To find the experimental wavelength I took the average of the five wavelengths (other four wavelengths are not shown), but now I am lost in trying to find the theoretical value for the wavelengths. Since we don't have an angle because we traced the interference patterns for a double slit, I couldn't use this equation (wavelength=dsin(theta)/m) for the theoretical wavelength. I am not sure which equation to use to find the theoretical wavelength. Please help I am so confused...
    Last edited: Nov 1, 2014
  2. jcsd
  3. Nov 3, 2014 #2


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    Hello Ronsa, and welcome to PF :)

    Glad to help if I can, but you have to help me in getting a clear picture what this is about. The problems statement is sort of mssing: you start with a list of variables.

    What have you measured ? h = 0.5 mm from the center of the pattern to the first maximum ? That's quite small, but who knows.

    How do you calculate the wavelength ? Visible red is more like ten times longer wavelengths...

    Then: "To find the experimental wavelength I took the average of the five wavelengths" Do you have five light sources ?
    What is your definition of experimental wavelength ? and of theoretical wavelength ?

    Why do you think you don't have an angle ?
    Can you post a drawing of the setup ? Or find a link that has a clear drawing ?
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