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What is Bandwidth? Write its value in the LCR circuit.

Answer
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Hint: In order to solve this question we need to understand Capacitance, inductor and resistance. Capacitor is an electrical device that is used to store energy in form of charges, an inductor is an electrical device which is used to store energy in the form of a magnetic field and resistance is as an electrical device which is used to derive current in circuit. So when the inductor, capacitor and resistance are connected in series with AC Voltage then it is known as LCR circuit. LCR circuit initially shows inductive behavior and later it shows capacitive behavior.

Complete step by step answer:
Bandwidth in an LCR circuit is defined as the difference between two half frequencies. Half frequencies are those frequencies for which the power dissipation is half the maximum value. To find the bandwidth of an LCR circuit, we need to find the resonant frequency and quality factor.Consider an inductor “L”, Capacitor “C” and Resistance “R” connected in series with each other.Let “Z” be the impedance in circuit, then we know Z can be written as;
Z=[R2+(XL2XC2)]12
Here, ω is the angular frequency in the circuit.

Resonance is the condition when the impedance of circuit is minimum and for this, Inductive reactance XL and capacitive reactance XC must become equal with each other.We know,
XL=ωL and XC=1ωC
Equating both we get, XL=XC
ωL=1ωC
ω2=1LC
ω=1LC
So the resonant frequency is, f=ω2π
f=12πLC
And the Quality factor is a quantity which shows the quality of circuit,
Q=XLR
Q=ωLR

Bandwidth is mathematically defined as ratio of resonant frequency and quality factor, denoted by
Δf=fQ
Putting values we get,
Δf=12πLCωLR
Putting the value of ω and solving we get,
Δf=R2πLC(1LCL)
Δf=R2πL

Note: It should be remembered that circuit behave as inductor first because initially uncharged inductor behave as closed circuit and initially uncharged capacitor behave as open circuit, so initially circuit behave as inductor and later o after resonance circuit behave as capacitor because the voltage across capacitor is building up.