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Assistant Geophysicist Solutions

 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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