What will be the value of time constant for the network shown below?

 

a. 5RC
b. 4RC
c. (4/5) RC
d. RC /5

ANSWER: (4/5) RC

Explanation:

By replacing the voltage source in terms of internal impedance, the equivalent circuit is shown below.

From the above equivalent network, it is obvious that

Req = (R x 4R) / 5R

= 4R /5

Also, the time constant (τ) = Req x C

= (4 /5) RC