Tiêu đề 22. Alternating Current.pdf ✅

1. In the given circuit the reading of voltmeter V1and V2 are 300 volts each. The reading of the Volt meter V3 and ammeter A are respectively: (1) 100 V, 2.0 A (2) 150 V, 2.2 A (3) 220 V, 2.2 A (4) 220 V, 2.0 A 2. The impedance of a circuit, when a resistance R and an inductor of inductance L are connected in series in an AC circuit of frequency f is :- 3. A complex current wave is given by i = 5 + 5 sin (100 t) A. Its average value over one time period is given as: (1) 10 A (2) 5 A (3) 50 A (4) 0 4. In a transformer, number of turns in the primary are 140 and that in the secondary are 280. If current in primary is 4A, then that in the secondary is (1) 4 A (2) 2 A (3) 6 A (4) 10 A 5. In a series LCR circuit, resistance R =  10 and the impedance R =  10 . The phase difference between the current and the voltage is (1) 30° (2) 45° (3) 60° (4) 90° 6. In the case of an inductor : (1) voltage lags the current by 2  (2) voltage leads the current by 2  (3) voltage leads the current by 3  (4) voltage leads the current by 4  A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion. B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion. C. If Assertion is True but the Reason is False. D. If both Assertion & Reason are False. 7. Assertion :- Inductive reactance of an inductor in DC circuit is zero. Reason :- Angular frequency of DC circuit is zero. (1) A (2) B (3) C (4) D 8. An L–C–R series circuit is at resonance with 10Veach across L, C and R. If the resistance is halved the respective voltages across L, C and R are :- (1) 10V, 10V and 10V (2) 20V, 20V and 5V (3) 20V, 20V and 10V (4) 5V, 5V and 5V 9. The value of L, C and R for a circuit are 1H, 9Fand 3. What is the quality factor for the circuit at resonance :- 10. In an a.c. LCR circuit a capacitor and an inductor in series are connected with an a.c. voltage source of 90 volts. An ammeter and a voltmeter are connected in the circuit to measure the current in the circuit and the voltage across the capacitor plusthe inductor combination. If XL = XC = 4  andR= 45  , the reading of ammeter (I) and thevoltmeter (V) are - (1) I = 2 amp. and V = 0 volt. (2) I = 2 amp. and V = 8 volt. (3) I = 2 amp. and V = 2 volt. (4) I = 3 amp. and V = 1 volt. 11. If E = 200Volt, R = 25  , L=2H and C=2μF and the frequency is variable then the current atf = 0 and f =  will be respectively – Alternating Current
(1) 0A, 8A (2) 8A, 0A (3) 8A, 8A (4) 0A, 0A 12. In LR circuit the current increases to one fourth of its maximum value in 4sec, then the timeconstant of the circuit is – 13. An L–C–R series circuit with 100 ohm resistance is connected to an ac source of 100 V and angular frequency 300 rad/s. When the capacitance is removed, the current lags behind the voltage by45°, when the inductance is removed; the current leads the voltage by 45°. The current flowing in the circuit when all the three are connected will be – (1) 1A (2) 1·5 A (3) 2A (4) 3 A 14. When an ac generator of 120 V is connected in series with a capacitor and a resistor of 30  , the circuit carries a current 1·5A. The potential difference across the capacitor will be – (1) 1·11 V (2) 111 V (3) Zero (4) 220 V 15. In the branch AB of a circuit, as shown in the figure, a current I = (t + 2) A is flowing, wheret is the time in second. At t = 0, the value of(VA–VB) write will be :- (1) 3v (2) –3v (3) –5v (4) 5v 16. In a circuit L, C and R are connected in series with an alternating voltage source of frequency f. The current leads the voltageby 45°. The value of C is 17. In circuit shown in figure the ac source gives a voltage V = 20 cos (2000 t). Neglecting source resistance, the voltmeter and ammeter reading will be (1) 0V, 0.47A (2) 1.68V, 0.47A (3) 0V, 1.4A (4) 5.6V, 1.4A 18. In the circuit shown switch S is connected to position2 for a long time and then joined to position 1. The total heat produced in resistance R1 is : 19. In a circuit an alternating current and a direct current are supplied together. The expression of the instantaneous current is given as i = 3 + 6 sin t. Then the r.m.s. value of the current is (1) 3A (2) 6A (3) 3 2A (4) 3 3A 20. In a series resonant LCR circuit, if L is increased by 25% and C is decreased by 20%, then the resonant frequency will :- (1) Increase by 10% (2) Decrease by 10% (3) Remain unchanged (4) Increase by 2.5%
21. An alternating e.m.f. of angular frequency  is applied across an inductance. The instantaneous power developed in the circuit has an angular frequency :- 22. In a L-R circuit the stored energy in the inductor coil is 5 Joule and rate of heat generation is10 Watt at a charge flow rate of one coulomb per second. The time constant of circuit is : (1) 2 sec (2) 1 sec (3) 1.5 sec (4) Data insufficient 23. Match the following Currents r.m.s values (A) x0 sint (i) x0 (B) x0 sint cost (ii) 0 2 x (C) x0 sint + x0 cost (iii) ( ) 0 2 2 x (1) (A → i), (B → ii), (C → iii) (2) (A → ii), (B → iii), (C → i) (3) (A → i), (B → iii), (C → ii) (4) None 24. The instantaneous values of current and potential difference in an alternating circuit are i = sin t and E = 100 cos t respectively. r.m.s. value of watt less current (in amp) in the circuit is :- (1) 1 (2) 1 2 (3) 100 (4) zero 25. The self inductance of a choke coil is 10 mH. When it is connected with a 10V dc source, then the loss of power is 20 watt. When it is connected with 10 volt ac source, then loss of power is 10watt. The frequency of ac source will be (1) 50 Hz (2) 60 Hz (3) 80 Hz (4) 100 Hz 26. Three inductances are connected as shown below. Assuming no coupling, the resultant inductance will be (1) 0.25 H (2) 0.75 H (3) 0.01 H (4) 1 H 27. An inductor, L a resistance R and two identical bulbs, B1and B2 are connected to a battery through as witch S as shown in the fig. The resistance R is the same as that of the coil that makes L. Which of the following statements gives the correct description of the happenings when the switch S is closed (1) The bulb B2 lights up earlier than B1 and finally both the bulbs shine equally bright (2) B1 light up earlier and finally both the bulbs acquire equal brightness (3) B2 lights up earlier and finally B1 shines brighter than B2 (4) B1 and B2 light up together with equal brightness all the time 28. What will be the impedance of the circuit shown below (1) 5 (2) 10 (3) 25 (4) 75 29. An ac voltage source of E = 150 sin 100 t is used to run a device which offers a resistance of 20 and restricts the flow of current in one direction only. The r.m.s. value of current in the circuit will be (1) 1.58 A (2) 0.98 A (3) 3.75 A (4) 2.38 A 30. A capacitor of capacitance 100 μF and a resistance of 100  is connected in series with A.C. supply of 220 V, 50 Hz. The current leads the voltage by:- (1) tan–1 (1/2  ) (2) tan–1 (1/  ) (3) tan –1 (2/  ) (4) tan–1 (4/  ) 31. A complex current wave is given by i = 5 + 5 sin (100 t) A. Its average value over one time period is given as : (1) 10 A (2) 5 A (3) 50 A (4) 0 32. The reading of ammeter in the circuit shown will be:-
(1) 2A (2) 2.4A (3) Zero (4) 1.7A 33. The output of a step - down transformer is measured to be 24V when connected to a 12W light bulb. The peak value of current is :- (1) 1 2 A (2) 2A (3) 2A (4) 2 2A 34. If a direct current of 'a' unit is super imposed with an alternating current I=' bsin  t' then effective value of resulting current is :- 35. A current in circuit is given by i = 3 + 4 sin  t. Then the effective value of current is : (1) 5 (2) 7 (3) 17 (4) 10 36. The graph shows variation of I with f for a series R-L-C network. Keeping L and C constant. If R decreases : (a) Maximum current (Im) increases (b) Sharpness of the graph increases (c) Quality factor increases (d) Band width increases (1) a, b, c (2) b, c, d (3) c, d, a (4) All 37. Time constant of the given circuit is . If the battery is replaced by an ac source having voltage V = V0 cos t, power factor of the circuit will be :- 38. A fully charged capacitor C with intial charge q0 is connected to a coil of self inductance L at t = 0. The time at which the energy is stored equally between the electric and the magnetic fields is :- 39. If the current through an inductor of inductance L is given by I = I0 sin  t, then the voltage across inductor will be :- 40. In an electrical circuit R, L, C and an a.c. 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 from the circuit the phase difference is again  /3. The power factor of the circuit is : (1) 1 (2) 3 / 2 41. As given in the figure, a series circuit connected across a 200 V, 60 Hz line consists of a capacitor of capacitive reactance 30  , a non-inductive resistor of 44  , and a coil of inductive reactance 90  and resistance 36  . The power dissipated in the coil is (1) 320 W (2) 176 W (3) 144 W (4) 0 W 42. In the case of an inductor : (1) voltage lags the current by 2  (2) voltage leads the current by 2  (3) voltage leads the current by 3  (4) voltage leads the current by 4 