Question

IV. TESTING EXPERIMENT: YOUNG’S DOUBLE SLIT EXPERIMENT The goal of this experiment is to test the relationships we just developed about the positions of the bright spots of an interference pattern. Available equipment: Laser pointer, plate with two closely-positioned narrow slits, whiteboard or white screen, meter stick, protractor. f) Design an experiment to test the relationship we just developed. Sketch the experimental set-up. g) Use the hypothesis to predict the outcome of the experiment. Show your work on your whiteboard. h) Perform the experiment, record the outcome, and compare it to the prediction. i) Make a judgment about the hypothesis based on the prediction and the outcome of the experiment.

Answer 1

Available equipment
   a. laser pointer
   b. plate with two closely positioned narrow slits
   c. whiteboard / white screen
   d. meter stick
   e. protractor

theoretically speaking, young's double slit experiment follows the following relation
           y = n*lambda*D/d

           here y is distance of the maxima from the center of the pattern
           n is number of the maxima
           lambda is the wavelength of the laser being used
           D is daistance between the screen and the slits
           d is the distance between the slits

f. to test the above relationship
   we can only change the distance between the screen and the slits, the wavelength of the light and hte slit width cant be changed
   so we arrange the appratus such that the laser is behind the slits and the screen is in front of the slits
   we should see youngs double slit pattern on the screen from the slits
   on doubling the distance between the screen and the slits, the distance between the maximas on the screen should double as well ( from the theoretical equation)

   the experimental setup is as under

g. from the hypothesis we can say, for the same n
   y1 = n*lambda*D1/d
   y2 = n*lambda*D2/d
   hence
   y1/y2 = D1/D2
   hence
   if D2 = 2*D1
   then
   y2 = 2*y1
   hence the distance between the slits shll become double if the distance between the screen and the slits is doubled
   this we can measure with the given scale

h. the following table is obtained while performing the experiment
   lambda = 500 nm
   d = 10^-3 m
   hence theoretically

   y = n*500*10^-9*D/10^-3
   y = nD/2 mm [ D is in m]

   sno       D    n    y            predicted y
   1       1m   1   0.48 mm    0.5 mm
   2       1m   2   0.99 mm    1 mm
   3       1m   3   1.3 mm        1.5 mm
   4       2m   1   0.98 mm    1 mm
   5       2m   2   1.99 mm    2 mm
   6       2m   3   2.91 mm    3 mm

i. since we can see the predicted value and values from the experiments are really close , we can say that out hpothesis regaring the behaviour of double slit experiment is correct within the limit of experimental error