A series LCR circuit containing 5.0H inductor, 80μF capacitor, and 40Ω resistor is connected to a 230 V variable frequency ac source. The angular frequencies of the source at which power transferred to the circuit is half the power at the resonant angular frequency are likely to be:
hard
Alternating Current
2021
physics
25 rad/s and 75 rad/s
50 rad/s and 25 rad/s
46 rad/s and 54 rad/s
42 rad/s and 58 rad/s
Explanation
To solve this problem, we need to determine the angular frequencies at which the power transferred to the circuit is half of the power at the resonant frequency.Given:• Inductance L=5.0H• Capacitance C=80μF=80×10−6F• Resistance R=40Ω• Voltage V=230VThe resonant angular frequency ω0 is given by:ω0=LC1Substitute the values:ω0=5.0×80×10−61ω0=0.00041ω0=0.021ω0=50rad/sAt resonance, the power P0 is given by:P0=2RV2The power at half the resonant power is 2P0.The power transferred to the circuit at any angular frequency ω is:P=R2+(Lω−Cω1)2V2RWe need to find ω such that P=2P0:R2+(Lω−Cω1)2V2R=4RV2Simplifying, we get:4R2=R2+(Lω−Cω1)23R2=(Lω−Cω1)2Taking square root on both sides:3R=∣Lω−Cω1∣This gives two equations:Lω−Cω1=3R(1)Lω−Cω1=−3R(2)Solving equation (1):Lω−Cω1=3RLω2−3Rω−C1=0This is a quadratic equation in ω.Solving using the quadratic formula:ω=2a−b±b2−4acHere, a=L,b=−3R,c=−C1ω=2L3R±3R2+C4LSubstitute the values:ω=2×5.03×40±3×402+80×10−64×5.0ω=10403±4800+250000ω=10403±254800Approximating the square root:ω=10403±504.78Calculate the two values:ω1=10403+504.78≈54rad/sω2=10403−504.78≈46rad/sTherefore, the angular frequencies are 46rad/s and 54rad/s.This corresponds to Option 3.
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