7.18 A circuit containing an 80 mH inductor and a 60 µF capacitor in series is connected to a 230 V, 50 Hz supply. The resistance of the circuit is negligible.

(a) Obtain the current amplitude and rms values.

(b) Obtain the rms values of potential drops across each element.

(c) What is the average power transferred to the inductor?

(d) What is the average power transferred to the capacitor?

(e) What is the total average power absorbed by the circuit? [‘Average’ implies ‘averaged over one cycle’.]

 

Here,

Inductance, 𝐿 = 80 mH

Capacitance, 𝐶 = 60 μF

rms voltage, 𝑉 = 230 V

Frequency, 𝑓 = 50 Hz

(a) ω=2πf=2π×50Hz=100πrads1

current amplitude,

Im=2×VrmsZ=Vrms2XLXC=230×2(100π×80×1031100π×60×106)=11.6A

rms current,

Irms=Im2=11.632=8.24A

(b) the rms value of potential drop across the inductor,

VLrms=Irms×XL=8.24×100π×80×103=207V

rms voltage across the inductor,

VCrms=Irms×XC=8.24×1100π×60×106=437V

(c) As the phase difference between voltage and current through the inductor
is π/2, the average power transferred over a complete cycle by the source to
The inductor will always be zero.

Pl,avg=0

(d) For 𝐶, voltage lags by 𝜋𝜋/2. As the phase difference between voltage and
current through the capacitor is 𝜋𝜋/2, the average power transferred over a
complete the cycle by the source to inductor will always be zero.

Pl,avg=0

(e) As there is no average power transfer over a complete cycle by the source
to the circuit elements, so the average power absorbed by the circuit is
zero.