Question

A series L-R-C circuit consists of a 226 Ω resistor, a 27.4 mH inductor, a 11.55 µF capacitor, and an AC source of amplitude 15 V and variable frequency. If the voltage source is set to 5.6 times the resonance frequency, the impedance of this circuit is: Express the answer as a whole number.

Answer 1

Answer: 363 Ω.

Explanation:

In a series AC circuit excited by a sinusoidal voltage source, the magnitude of the impedance is found to be as follows:

Z = √((R^2 )+〖(XL-XC)〗^2) (1)

In order to find the values for the inductive and capacitive reactances, as they depend on the frequency, we need first to find the voltage source frequency.

We are told that it has been set to 5.6 times the resonance frequency.

At resonance, the inductive and capacitive reactances are equal each other in magnitude, so from this relationship, we can find out the resonance frequency fo as follows:

fo  = 1/2π√LC = 286 Hz

So, we find f to be as follows:

f = 1,600 Hz

Replacing in the value of XL and Xc in (1), we can find the magnitude of the impedance Z at this frequency, as follows:

Z = 363 Ω