Tiêu đề 23. Alternating Current Medium.pdf ✅

1. The phase relationship between current and voltage in a pure resistive circuit is bets represented by (a) (b) (c) (d) 2. A light bulb is rated at 100 W for a 220 V ac supply. The resistance of the bulb is (a) 284  (b) 384  (c) 484  (d) 584  3. In an ac circuit, V and I are given by V = 150 sin (150t) V and I = 150 sin A 3 150        + The power dissipated in the circuit is (a) 106 W (b) 150 W (c) 5625 W (d) Zero 4. Alternating voltage (V) is represented by the equation (a) t m V(t) V e  = (b) V(t) V sin t = m  (c) V(t) V cot t = m  (d) V(t) V tan t = m  where Vm is the peak voltage 5. An ac source of voltage V = Vm sin is connected across the resistance R as shown in figure. The phase relation between current and voltage for this circuit is (a) Both are in phase (b) Both are out of phase by 90° (c) Both are out of phase by 120° (d) Both are out of phase by 180° 6. In which of the following circuits the maximum power dissipation is observed? (a) Pure capacitive circuit (b) Pure inductive circuit (c) Pure resistive circuit (d) None of these 7. A 100 resistor is connected to a 220 V, 50 Hz ac supply. The rms value of current in the circuit is (a) 1.56 A (b) 1.56 A (c) 2.2 A (d) 2.2 mA 8. The peak voltage of an ac supply is 440 V, then its rms voltage is (a) 31.11 V (b) 311.1 V (c) 41.11 V (d) 411.1 V 9. The rms value of current in an ac circuit is 25 A, then peak current is (a) 35.36 mA (b) 35.36 A (c) 3.536 A (d) 49.38 A 10. An alternating voltage given by V = 140 sin 314 t is connected across a pure resistor of 50 the rms current through the resistor is (a) 1.98 A (b) 5.63 A (c) 8.43 A (d) 2.39 A 11. The line that draws power supply to your house from street has (a) 220 2V average voltage. (b) 220 V average voltage. (c) Voltage and current out of phase by / 2 (d) Voltage and current possibly differing in phase  such that . 2 | |    12. An ac source is of V,50 Hz. 2 200 The value of voltage after s 600 1 from the start is (a) 200 V (b) V 2 200 (c) 100 V (d) 50 V 13. If V = 100 sin (100t) V and mA 3 I 100sin 100t        = + are the instantaneous values of voltage and current, then the rms values of voltage and current are respectively (a) 70.7 V, 70.7 mA (b) 70.7 V, 70.7 A (c) 141.4 V, 141.4 mA (d) 100 V, 100 mA 14. The voltage over a cycle varies as ω V V sinωt for 0 t 0  =   ω 2 t ω V sinωt for 0     = − The average value of the voltage for one cycle is (a) 2 V0 (b) 2 V0 (c) Zero (d)  0 2V
15. The rms value of potential difference V shown in the figure is (a) 3 V0 (b) V0 (c) 2 V0 (d) 2 V0 16. The relation between an ac voltage source and time in SI units is V = 120 sin (100t)cos(100t) V. The value of peak voltage and frequency will be respectively (a) 120 V and 100 Hz (b) Vand 100Hz 2 120 (c) 60 V and 200 Hz (d) 60 V and 100 Hz 17. In the case of an inductor (a) Voltage lags the current by 2  (b) Voltage leads the current by 2  (c) Voltage leads the current by 3  (d) Voltage leads the current by 4  18. An inductor of 30 mH is connected to a 220 V, 100 Hz ac source. The inductive reactance is (a) 10.58 (b) 12.64 (c) 18.85 (d) 22.67 19. Switch S is closed at t = 0. After sufficiently long time, an iron rod is inserted into the inductor L. Then, the light bulb (a) Glows more brightly (b) Gets dimmer (c) Glows with the same brightness (d) Get momentarily dimmer and then glows more brightly 20. Which of the following graphs represents the correct variation of inductive reactance XL with frequency ? (a) (b) (c) (d) 21. A 44 mH inductor is connected to 220 V, 50 Hz ac supply. The rms value of the current in the circuit is (a) 12.8 A (b) 13.6 A (c) 15.9 A (d) 19.5 A 22. A coil of 0.01 H inductance and 1 resistance is connected to 200 V, 50 Hz ac supply. The time lag between maximum alternating voltage and current is (a) s 250 1 (b) s 300 1 (c) s 200 1 (d) s 350 1 23. An ideal inductor is in turn put across 200 V, 50 H and 220 V, 100 Hz supplies. The current flowing through it in the two cases will be (a) Equal (b) Different (c) Zero (d) Infinite 24. A circuit is made up of a resistance 1 and inductance 0.01 H. An alternating voltage of 200 V at 50 Hz is connected then the phase difference between the current and the voltage in the circuit is (a) tan ( ) 1  − (b)      −   2 tan 1 (c)      −   4 tan 1 (d)      −   3 tan 1 25. A coil of inductance 300 mH and resistance 2 is connected to a source of voltage 2 V. The current reaches half of its steady state value in (a) 0.15 s (b) 0.3 s (c) 0.05 s (d) 0.1 s 26. A 5 F capacitor is connected to a 200 V, 100 Hz ac source. The capacitive reactance is (a) 212  (b) 312  (c) 318  (d) 412  27. In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be (a) Remains same (b) Doubled (c) Halved (d) Zero

(c) Remains constant (d) None of these 46. In series LCR circuit, the phase angle between supply voltage and current is (a) R X X tan L − C  = (b) XL XC R tan −  = (c) XL XC R tan +  = (d) R X X tan L + C  = 47. In series LCR circuit, the plot of m l vs  is shown in the figure. The bandwidth of this plot will be (a) Zero (b) 0.1rad 1 s − (c) 0.2rad 1 s − (d) 0.4rad 1 s − 48. An electrical device drawn 2 kW power from ac mains voltage k223 V (rms). The current differs lags in phase by        = − − 4 3 tan 1 as compared to voltage. The resistance R in the circuit is (a) 15  (b) 20  (c) 25  (d) 30  49. As the frequency of an ac circuit increase , the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit? (a) Resistor and inductor (b) Resistor and capacitor (c) Resistor, inductor and capacitor (d) None of these 50. 200 V ac source is fed to series LCR circuit having XL =50  ,and R= 25  . Potential drop across the inductor is (a) 100V (b) 200V (c) 400V (d) 10V 51. A pure resistive circuit element X when connected to an ac supply of peak voltage 200V gives a peak current of 5A which is in phase with the voltage . A second circuit element Y, when connected to the same ac supply also gives the same value of peak current but the current lags behind by 0 90 .If the series combination of X and Y is connected to the same supply, what will be the rms value of current? (a) A 2 10 (b) A 2 5 (c) A 2 5 (d) 5 A 52. A 100 F capacitor in series with a 40  resistor is connected to a 100 V, 60 Hz supply. The maximum current in the circuit is (a) 2.65A (b) 2.75A (c) 2.58A (d) 2.95A 53. The Q factor of a series LCR circuit with L = 2 H, C= 32 F and R= 10  is (a) 15 (b) 20 (c) 25 (d) 30 54. An LCR series ac circuit is at resonance with 10 V each across L, C and R. If the resistance is halved , the respective voltage across L, C and R are (a) 10 V,10 V and 5V (b) 10 V, 10 V and 10 V (c) 20V, 20 V and 5 V (d) 20 V, 20 V and 10 V 55. An inductor 200mH, capacitor 500 F and resistor 10  are connected in series with a 100V variable frequency ac source. What is the frequency at which the power factor of the circuit is unity? (a) 10.22Hz (b) 12.4Hz (c) 19.2Hz (d) 15.9Hz 56. In a series LCR circuit the voltage across an inductor, capacitor and resistor are 20V,20V and 40V respectively The phase difference between the applied voltage and the current in the circuit is (a) 0 30 (b) 0 45 (c) 0 60 (d) 0 0 57. Figure shows a series LCR circuit connected to a variable frequency 230 V source. The source frequency which drives the circuit in resonance is (a) 4 Hz (b) 5 Hz (c) 6 Hz (d) 8 Hz 58. In a series LCR circuit the voltage across the resistance, capacitance and inductance is 10 V each. If the capacitance is short circuited , the voltage across the inductance will be (a) 10 V (b) 10 2 V (c) (10 2)V (d) 20 V 59. In the series LCR circuit shown the impedance is (a) 200  (b) 100  (c) 300  (d) 500  60. In an electrical circuit, R, L, C and ac voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and the current in the circuit is 3  .If instead, C is removed form the circuit, the phase difference is again . 3  The power factor of the circuit is (a) 2 1 (b) 2 1 (c) 1 (d) 2 3