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]
(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