0
\$\begingroup\$

The switch S has been closed for a long time, and the it is opened. I want to calculate the time constant for the RC circuit below. I don't know how to tackle this problem, is the time constant for an RC circuit always RC, no matter how the circuit looks? If yes, is R and C the equivalent resistans and capacitance one gets when reducing the circuit to one containing a resistor and capacitor in series?

enter image description here

\$\endgroup\$
6
  • 1
    \$\begingroup\$ When the switch is open, the circuit is just the capacitor in parallel to (R1 + R2) || (R3 + R4). (Oh well, in this case "in parallel" is the same as "in series") \$\endgroup\$
    – Eugene Sh.
    Commented Mar 11, 2021 at 18:26
  • \$\begingroup\$ @EugeneSh. thanks for the comment. What do you mean with parallel being the same as in series? \$\endgroup\$
    – Pi314
    Commented Mar 11, 2021 at 18:30
  • \$\begingroup\$ If you take just one resistor and one capacitor and connect them into a closed circuit - how would they be connected, in parallel or in series? \$\endgroup\$
    – Eugene Sh.
    Commented Mar 11, 2021 at 18:33
  • \$\begingroup\$ I think @EugeneSh. meant R1//R2 = Ra on the left and R3//R4 = Rb on the right then T= (Ra+Rb)C \$\endgroup\$ Commented Mar 11, 2021 at 18:46
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 If the switch is open R1 is in series with R2 (on the top) and R3 is i series with R4 (on the bottom) \$\endgroup\$
    – Eugene Sh.
    Commented Mar 11, 2021 at 18:48

1 Answer 1

1
\$\begingroup\$

Apply Thevenin you will get a voltage source applied to a capacitor through a resistor and then the time constant is trivial. You just need to know where to apply Thevenin.

\$\endgroup\$
2
  • \$\begingroup\$ Thevenin theorem is not a part of my course unfortunately, is there any other way to do it? \$\endgroup\$
    – Pi314
    Commented Mar 11, 2021 at 19:18
  • \$\begingroup\$ @Pi314 Not that Thevenin is really needed here, but I am surprised it is not part of your course. It should be a part of the very first electrical circuits course as a basic circuit analysis tool. \$\endgroup\$
    – Eugene Sh.
    Commented Mar 11, 2021 at 19:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.