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

The correct option is C Resistor, inductor and capacitor

Impedance of an LCR ciorcuit is given by

$Z=\sqrt{R^2+(X_l-X_C{)}^2}$

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

The variation of Z with $\upsilon$ is shown in the 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 current decreases. Hence ,

the combination of circuit elements is most likely to comprise

the circuit are R, L and C .