Hi
Please, I need help to understand this issue. I made some exercises on Thévenin equivalent but I'm stuck in this one.
Here I attached two files taken off from O'Malley's book ("Basic circuit analysis" edited by schaum...) (pages 103-104)
I have two doubts:
First - why we consider the 30 V from 30 voltage if we DON'T consider the 8-resistor? "The 8-22 resistor has no effect on this voltage because there is zero current flow through it as a result of the open circuit." It is ok, but if there is no current why we must consider the 30 V to calculate V th?
I= V / R if there is no current therefore 0 A = 30V / R internal (of the voltage source). Confused. :|
Second - Why you cannot consider the "5-R and 4-R resistors" to calculate the Vth? O'Malley said that "Notice that the 5-R and 4-R resistors have no effect on VTh." but no explanation given.
I thought that the correct would be:
(V - 100)/10 + V / 40 + 20 + V / 5 = 0 (the 4-resistor was not used, because we have the current known... I think.)
Why not put Vth = -20 * 4 = -80 V? Directly... I confused about the adding of 30 V if there is no current in that voltage source...
Concerning Rth, no problem.
Thanks for your help,
Jorge Almeida
Please, I need help to understand this issue. I made some exercises on Thévenin equivalent but I'm stuck in this one.
Here I attached two files taken off from O'Malley's book ("Basic circuit analysis" edited by schaum...) (pages 103-104)
I have two doubts:
First - why we consider the 30 V from 30 voltage if we DON'T consider the 8-resistor? "The 8-22 resistor has no effect on this voltage because there is zero current flow through it as a result of the open circuit." It is ok, but if there is no current why we must consider the 30 V to calculate V th?
I= V / R if there is no current therefore 0 A = 30V / R internal (of the voltage source). Confused. :|
Second - Why you cannot consider the "5-R and 4-R resistors" to calculate the Vth? O'Malley said that "Notice that the 5-R and 4-R resistors have no effect on VTh." but no explanation given.
I thought that the correct would be:
(V - 100)/10 + V / 40 + 20 + V / 5 = 0 (the 4-resistor was not used, because we have the current known... I think.)
Why not put Vth = -20 * 4 = -80 V? Directly... I confused about the adding of 30 V if there is no current in that voltage source...
Concerning Rth, no problem.
Thanks for your help,
Jorge Almeida
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