Q. A coil of inductive reactance 31 Ω has a resistance of 8 Ω. It is placed in series with a condenser of capacitative reactance 25 Ω. The combination is connected to an a.c. source of 110 V. The power factor of the circuit is :
A) 0.40
B) 0.128
C) 0.80
D) 0.66
Explanation
[Solution from source] The net reactance is X_L − X_C = 31 − 25 = 6 Ω, so Z = √(8² + 6²) = 10 Ω. The power factor is cos φ = R/Z = 8/10 = 0.80. Using X_L + X_C would give a much smaller value; the supply voltage is not needed. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.