Question

As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit ?
A. Resistor and inductor
B. Resistor and capacitor
C. Resistor, inductor and capacitor
D. None of these

Answer 1

Correct Answer - C
Impedance of an LCR circuit is given by
`Z=sqrt(R^(2)+(X_(L)-X_(C ))^(2))`
`=sqrt(R^(2)+(2pi upsilon L-(1)/(2pi upsilon C))^(2))`

The variation of Z with `upsilon` is shown in figure.
As`upsilon` increases, Z decreases and hence current increases.
At `upsilon = upsilon_(r ),Z` is minimum, current is maximum. Beyond `upsilon = upsilon_(r )` Z increases and currents is most likely to comprise the circuitare R, L and C.