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Homework Help: Lloyd single Mirror

  1. Dec 2, 2012 #1
    1. The problem statement, all variables and given/known data: In a loud single mirror exp. a bright fringe of width 0.2 mm is seen at a point on the screen kept at a distance 1.0 m from the source. When the mirror is raised up to increase the angle of incidence at any point of the mirror by a dist. of 0.9 mm, fringe width of the same fringe becomes 0.5 mm, find the wavelength of the source.

    2. Relevant equations: wavelenght = distance between the two slits (a) * fringe width (X) / distance from source to screen (D)

    3. The attempt at a solution: How to find the distance between the two slits? Should I be proceeding by finding "a" by a= incidence angle*D?
  2. jcsd
  3. Dec 2, 2012 #2


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    Welcome to Physics Forums.

    You can use the first equation you wrote,
    ... and write it twice, because there are two situations:
    (1) the distance between the "slits" is a
    (2) the distance between the "slits" is ____ [where you fill in the blank here].
  4. Dec 2, 2012 #3
    Thanks Redbelly98 for the quick reply.

    Is the answer: wavelength = 6000 A correct?

    wavelength = 2*a*X/D
    Therefore, 2*a*0.2/1000=2*(a-0.9)*0.5/1000
    which gives, a=1.5 or 2*a = 3.0
    so, wavelength =3.0*0.2/1000
    =6000 A
  5. Dec 2, 2012 #4


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    Looks good!

    You may need to better explain how you worked the units, if you submit your homework to be graded or have to work a similar problem on an exam someday.
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