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Alternating Current question

2006 · Q139
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Alternating Current question

2006 · Q139

NEETPhysicsAlternating CurrentMCQ+4 / −1
A coil of inductive reactance 31 Ω\OmegaΩ has a resistance of 8 Ω\OmegaΩ. It is placed in series with a condenser of capacitative reactance 25 Ω\OmegaΩ. The combination is connected to an a.c. source of 110 V. The power factor of the circuit is
  1. A
    0.33
  2. B
    0.56
  3. C
    0.64
  4. D
    0.80
View written solutionFree

Correct answer: D

Impedance of series LCR is

Z = R2+(XL−XC)2\sqrt {{R^2} + {{\left( {{X_L} - {X_C}} \right)}^2}} R2+(XL​−XC​)2​

= 82+(31−25)2\sqrt {{8^2} + {{\left( {31 - 25} \right)}^2}} 82+(31−25)2​

= 64+36\sqrt {64 + 36} 64+36​ = 10 Ω\Omega Ω

Power factor, cosϕ\phi ϕ = RZ=810=0.8{R \over Z} = {8 \over {10}} = 0.8ZR​=108​=0.8

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