Homework Set # 12 - Not Due – Solutions Available on November 25

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1) Let F(ω) be the Fourier (exponential) transform of f(x) and G(ω) be the Fourier transform of g(x)=f(x+a). Show that G(ω)=e-iaωF(ω).

Solution (pdf format)

    2) 20.2.2

    3) 20.2.4

    4) 20.2.7

    5)
    20.2.8

    6)
    20.3.6

    7) For a point source at the origin, the three-dimensional neutron diffusion equation becomes

    -D∆2φ(r)+K2Dφ(r)=Qδ(r),

    2 stands for the Laplacian. Apply a three-dimensional Fourier transform. Solve the transformed equation. Transform the solution back into r-space.

    Solution (pdf format)


    8)  a) Consider the function f(x)=1 for |x|<1 and 0 otherwise.

             1) Can you expand f(x) in terms of a sine Fourier transform? Why?

             2) What Fourier transform should you use? Calculate this FT for f(x).

         b) Now consider f(x)=1 for a<x<b with a>0 and b>0 and f(x)=0 otherwise.

             1) Can you expand f(x) in terms of a sine FT? Why?

             2) If the answer to the previous question is yes perform the FT.

             3) For what values of x is your sine transform appropriated?

             4) What assumption are you making about f(-x)?

             5) Can you expand f(x) as a cosine FT? What assumption do you need to make about f(-x)?

             6) If you wanted to obtain a FT of f(x) valid for all x what FT should you use? Why? Find the coefficients .


    Solution (pdf format)