Question

As the frequency of an ac circuit increase , 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

Answer: (C)

Resistor, inductor and capacitor

Answer 2

: Impedance of an LCR circuit is given by

$Z = \sqrt{R^{2} + (X_{L} - X_{C})^{2}}$

$= \sqrt{R^{2} + \left( 2\pi\upsilon L - \frac{1}{2\pi\upsilon C} \right)^{2}}$

The variation of Z with $\upsilon$is shown in figure.

As $\upsilon$increases Z decreases and hence current increases. At $\upsilon = \upsilon_{r},$ A is minimum, current is maximum. Beyond $\upsilon = \upsilon_{r}$Z increases and current decreases. Hence, the combination of circuit elements is most likely to comprise the circuit are R, L and C.