104. The Laplace Transform of unit step function is:
(a) 1
(b) \frac{1}{s}
(c) \frac{1}{s^{2}}
(d) \frac{1}{s^{3}}
(Thanks to Pragnath, AU)
Solution: -
The Laplace transform is a mathematical tool which is used to convert
the differential equation in time domain into the algebraic equations in the frequency
domain. if x(t) is
a time-domain function, then its Laplace transform is defined as
X_{(s)} = L[u(t)] =
\int_{0}^{\infty}~u(t)e^{-st}~dt
The unit step function is defined as,
u(t) = 0, for t < 0
1, for t ≥ 0
Therefore, by the definition of the Laplace transform, we get,
X_{(s)} = L[u(t)] =
\int_{0}^{\infty}~u(t)e^{-st}~dt
\Rightarrow~L[u(t)]~=~\int_{0}^{\infty} e^{-st}~dt~=~[\frac{e^{-st}}{-s}]_0^\infty
\Rightarrow~L[u(t)]~=~[\frac{e^{\infty}-e^0}{-s}]~=~\frac{1}{s}
Therefore the answer is
option (b) \frac{1}{s}
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