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Network Elements and the Concept of Circuit

  1. If the unit step response of a network is (1 – e–αt), then its unit impulse response will be—
    1. α e– αt
    2. 1
      e–t/α
      α
    3. 1
      αe–t/α
    4. (1 – α) e– αt
Correct Option: A

In order to calculate the unit impulse response first we will obtain transfer function i.e. H (S)
given y (t) = 1 – e– α t

Y (s) =
1
-
1
=
α

ss2 (s + α) s(s + α)

we know that
H (s) =
Y (s)
X (s)

X (t) = u (t)
X (s) =
1
s

so, H (s) =
α
=
α
S(s + α) 1 / Ss + α

Now, according to the question
x (t) = δ (t)
so, X (s)=1
Y (t)=?
Now, Y (s) = H (S) X (S)
or Y (S) =
α
. 1
s + α

or Y (S) =
α
s + α

or Y (t) = α. e– αt



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