Class 12 Physics
CBSE and UP Board
Alternating Current
Chapter-7 Exercise 7.9
NCERT Solutions for Class 12 Physics Chapter 7 Question 9
A series LCR circuit with R = 20 Ω, L = 1.5 H and C = 35 μF is connected to a variable frequency 200 V ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?
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At resonance, the frequency of the supply power equals the natural frequency of the given LCR circuit.
Resistance, R = 20 Ω
Inductance, L = 1.5 H
Capacitance, C = 35 μF = 30 x 10_6F
AC supply voltage to the LCR circuit, V = 200 V
Impedance of the circuit is given by the relation,
Z = √ [R2 + (xL-xc)2 ]
At resonance, XL = Xc
:.Z = R = 20 Ω
Current in the circuit can be calculated as:
I = V/Z = 200/20= 10 A
Hence, the average power transferred to the circuit in one complete cycle:
VI = 200 x 10 = 2000 W.