Thread Starter

shiva bharadwaj

Joined Sep 29, 2008
hi guys
while solving problems in laplace transforms we usually substitute s=jω but actually s=σ+jω why are we neglecting σ here?
what is its significance?


Joined Feb 2, 2008
A particular example might help with getting a clear crisp answer, but generally, that sigma helps make an the integral converge. The result doesn't depend on the value of sigma; like limits in beginning calculus, you can't just throw in zero, but approach it carefully. I hope that makes sense...


Joined Mar 20, 2007
shiva bharadwaj,

While solving problems in Laplace transforms, we usually substitute s=jω. But actually s=σ+jω. Why are we neglecting σ here?
What is its significance?
Notice how I inserted capitalization and punctuation in your question. Sigma is not being neglected, it is just zero for sinusoidal waveforms. The substitution is NOT made for nonsinusoidal functions. You did not mention that. Any good book on Laplace transforms will show you why substitution of jw in a Laplace expression gives the phasor representation of that function.