Question

When the frequency of the ac voltage applied to a series LCR circuit is gradually increased from a low value , the impedance of the circuit.
A. monotonically increases
B. first increases and then decreases
C. first decreases and then increases
D. monotonically decreases

Answer 1

Correct Answer - C
We Know`Z=sqrt((omegaL-1/(omegaC))^2+R^2)`
IF , `(dZ)/(domega)=0`then `omega=1/sqrt(LC)`
when `omegalt1/sqrt(LC)` then `(dZ)/(domega)le0` i.e., Z is a decreasing function. Again, when `omegagt1/sqrt(LC)`then`(dZ)/(domega)gt0` i.e., Z is a increasing function.