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Fourier transform of rectangular pulse (Waves)

  • Thread starter tigger88
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  • #1
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Homework Statement



F(w) is the Fourier transform of f(t). Write down the equation for F(w) in terms of f(t).
A rectangular pulse has height H and total length t0 in time. Show that as a function of w, the amplitude density is propertional to sinc(wt0/2).

Homework Equations



F(w) = integral from -infinity to +infinity of: f(t)exp(-iwt)dw

The Attempt at a Solution



integral from -t0/2 to +t0/2 of: h*exp(-iwt)dw

I have access to the solution to this problem, which says that it should be:
integral from -t0/2 to +t0/2 of: h*exp(-iwt)dt,
but I don't understand why I'm integrating wrt t now, when the definition says w.

Could somebody please explain this?

Thanks in advance.
 

Answers and Replies

  • #2
Cyosis
Homework Helper
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Where do you get that definition from? Think about it, you want to find a function [itex]F(\omega)[/itex], but if you calculate the integral you've written down as the "definition" then the integration boundaries will be inserted into [itex]\omega[/itex] after the integration. As as a result you won't have a function with variable [itex]\omega[/itex].

The correct definition is (normalization conventions can be different):
[tex]
F(\omega)}=\int_{-\infty}^\infty e^{-i \omega t} dt
[/tex]
 
  • #3
21
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Actually I got that definition from the solution to the question. It makes a whole lot more sense now, thanks for your reply!
 

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