Q.

A series R-C combination is connected to an AC voltage of angular frequency ω=500 rad/s. If the impedance of the R-C circuit is R1.25, the time constant (in millisecond) of the circuit is                         [2011]


Ans.

(4)

Time constant, T=RC

Impedance Z=R2+(1ωC)2

Given Z=R1.25

∴  R1.25=R2+(1ωC)2

∴ RC=2ω=2500×1000 ms

∴ RC=4 ms