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Control system miscellaneous

  1. Let the Laplace transform of a function f(t) which exists for t > 0 be F1 (s) and the Laplace transform of its delayed version f(t – π) be F2 * (s). Let F1 * (s) be the complex conjugate of F1 (s) with the Laplace variable set as s = σ + jω.
    G(s) =
    F2(s).F1*(s)
    , then the inverse Laplace transform of G(s) is
    |F1(s)|2
    1. an ideal impulse δ(t)
    2. an ideal delayed impulse δ(t – τ)
    3. an ideal step function u(t)
    4. an ideal delayed step function impulse u(t – τ)
Correct Option: B

F2 (t) = L{f(t – τ)} = e – Sτ F1 (S)

G(s) =
e– sτ F1 (s) . F1* (s)
= e– sτ
|F1 (s)|2

G(t) = L– 1 {G(S)} = δ(t – τ)



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