Young' s  Experiment Model
This model is based on the equation given below for the electric field of  a point source of light on a screen a distance (L) from the screen .  λ is the wavelength of the light, d is the distance each slit is from the x axis,  
    and y is the y axis .  
        All units are in meters.

(E^(I ((2  π)/λ) (Sqrt[(L^2) + (((y - d))^2)])))

The model below plots the intensity of the light from multiple slits on a screen a distance L away .  
        To modify the model below,  choose the distance L,  
    wavelength λ,  number of slits n,  
    and the spacing between each slit d, 
    modify the values accordingly . 
When you are ready to see the plot press the enter key on the number pad.

L = 50;
λ = 670*(10^(-9));
n = 11;
d =  .001;
ClearAll[y]
f[y_, 
        d_] := (E^(I ((2  π)/λ) (Sqrt[(L^2) + (((y - d))^2)])))
If[EvenQ[
        n], 
a = -n/2; 
Z[y_] = 
        f[y, a*d + d/2]; 
Do[
        Z[y_] = Z[y] + f[y, (a + b) d + d/2], {b, 
          n - 1}];, 
a = -Mod[n, 
            2]; 
Z[y_] = f[y, a*d]; 
Do[
        Z[y_] = Z[y] + f[y, (a + b) d], {b, 
          n - 1}];]
Plot[(Abs[Z[y]*Conjugate[Z[y]]])^2, {y, - .005 L,  .005  
            L}];

This model plots the intensity of the light along the y axis .  To modify the model below,  choose the  wavelength λ,  
    number of slits n,  and the spacing between each slit d, 
    modify the values accordingly .  
        To domain of the plot will start at zero and go to the value assigned to c,  
    change the value of c to modify the domain of the plot .  
        When you are ready to see the plot press the enter key on the number pad.

λ = 680*(10^(-9));
n = 5;
d =  .001;
c = 10;
ClearAll[L]
y = 0;
f[L_, 
        d_] := (E^(I ((2  π)/λ) (Sqrt[(L^2) + (((y - d))^2)])))
If[EvenQ[
        n], 
a = -n/2; 
Z[L_] = 
        f[L, a*d + d/2]; 
Do[
        Z[L_] = Z[L] + f[L, (a + b) d + d/2], {b, 
          n - 1}];, 
a = -Mod[n, 
            2]; 
Z[L_] = f[L, a*d]; 
Do[
        Z[L_] = Z[L] + f[L, (a + b) d], {b, 
          n - 1}];]
Plot[(Abs[Z[L]*Conjugate[Z[L]]])^2, {L, 0, c}];