# step response of an RC circuit

#### PG1995

Joined Apr 15, 2011
816
Hi

Please have a look on the attachments. The attached pages are: 258, 259, 260. Please help me with the queries. I need to understand this derivation soon. Thank you for your help.

If you want to have a look on the derivation of "Source Free RC Circuit" and description of "natural response", you can have look on the attached pages in first post of this thread: http://forum.allaboutcircuits.com/showthread.php?t=61060

Regards
PG

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#### Papabravo

Joined Feb 24, 2006
13,554
u(t) is the universally recognized notation for the unit step function.
It has only two values, zero and 1.
Rich (BB code):
u(t) = 0, for all t < 0
u(t) = 1, for all t > 0

What happens at t = 0 may be defined somewhat arbitrarily.
It could be zero, one or some value in between like say 0.5
Since 1 is the multiplicative identity over the field of real numbers it can be ignored for t > 0 and that is what the author is doing.