Page 415 - Basic Electrical Engineering

[Ans R = 460 A, L = 2.229 H, C = 4.549 μF]

48. A 200 V, a variable frequency supply is connected across an L–R–C series circuit with R = 10
Ω, L = 10 mH, and C = 1 mF. Calculate the frequency at which reasonance will occur. Also
calculate the Q-factor and bandwidth.

[Ans f = 1591.5 Hz, Q-factor = 10, Bandwidth = 159 H ]
Z

49. A coil of R = 10 Ω, L = 0.023 H connected in parallel with another coil of R = 5 Ω, L = 0.035
H. The combination is connected across at 200 V, 50 Hz supply. Calculate the current drawn
from the supply and the power factor.

[Ans I = 31.4 A, P.f. = 0.63 lagging]

50. A coil of resistance 20 Ω and inductance of 300 mH is connected in parallel with a
capacitance of 200 μF. The combination is connected across 200 V, variable frequency power
supply. At what frequency will the parallel circuit resonate and what would be the current at
resonance?

[Ans 20.5 Hz, 2.66 A]

51. Calculate the value of R in the circuit shown in figure below such that the circuit will resonate.

Figure 3.77

[Ans R = 6 Ω.]

52. Calculate the half power frequencies of a series resonance circuit in which the resonant
frequency is 150 KHz and bandwidth 75 KHz.

[Ans f =117 KHz, f = 19 KHz]
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C. Multiple Choice Questions