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Young's Double Slit Experiment - Slit Separation Calculation

  1. Feb 24, 2011 #1
    1. The problem statement, all variables and given/known data

    Calculate the slit separation (d) given that:

    Wavelength = 650 nm (Plugged in 6.5*10^-7 m)
    m = 1 (plugged in 1)
    Distance to screen (D) = 37.5 cm (plugged in 0.375m)
    Distance between centre to side order (y) = 0.7 cm (pluged in 0.007m)

    2. Relevant equations

    We were only given one equation in our lab manual (the same equation they gave us for a single slit, slit width problem....except instead of d they had a there to represent slit width)

    d = (m*Wavelength*D)/y

    where d is the slit separation

    3. The attempt at a solution

    I plugged in the numbers and I produced a solution equal to 0.0348 mm. (I made sure to convert to meters before plugging into the equation and then converted back to milimetres by multiplying by 1000)

    What ails me is that the theoretical, or given slit separation is 0.25mm. This makes my relative error aproximately 88% and I am positive I did not do the experiment that poorly. Surprisingly though, the answer produced is VERY similar to the given SLIT WIDTH (0.04mm).

    Now I checked this a million times and I think I may be stuck in a rut of not seeing something that is supremely obvious but is making me get the wrong answer. Or the person who designed my lab did not supply me with a proper equation to solve this problem.

    Any help is appreciated.
  2. jcsd
  3. Feb 25, 2011 #2


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    Distance between centre to side order (y) = 0.7 cm (pluged in 0.007m)

    Can you show, how did you get the above value?
  4. Feb 25, 2011 #3
    Well, all this data comes from an experiment. Basically what happened was we had a laser shoot through a slit. It diffracted and left a pattern of lights on a white sheet of paper. What we did then was mark each of these lights with a pencil (up to m=2). We then measured the distance between the two marked lines (m1 on the left to m1 on the right). To get the value of y we had to divide this number in 2 (to get the distance to the center).

    What was measured for 2y (the distance between two of these ticks) was 1.4cm.

    So I did:

    1.4cm/2 = 0.7cm
    0.7cm/100 = 0.007m
    Last edited: Feb 25, 2011
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