AC Circuits Questions and Answers

78 A charged 30 uF capacitor is connected to a 27 mH inductor The angular frequency of free oscillations of the circuit is a 1 1 x 10 rad s c 3 1 x 10 rad s b 2 1 x 10 rad s d 4 1 x 10 rad s 79 An LC circuit contains a 40 mH inductor and a 25 F capacitor The resistance of the circuit is negligible

58 A series LCR circuit has R 5 2 L 40 mH and C 1 F the bandwidth of the circuit is a 10 Hz b 20 Hz c 30 Hz d 40 Hz In ICB circuit if re rer quality factor

59 The current flowing in a wire fluctuates sinusoidally as shown in the diagram The root mean square value of the current is i A 210 io Cari 2 1 1 2 c 2 2 io A t s b io 2 1 1 2 1 2 0 40 2 2 1 io

42 A 100 F capacitor in series with a 40 92 resistor is connected to a 100 V 60 Hz supply The maximum current in the circuit is a 2 65 A c 2 85 A b 2 75 A d 2 95 A

5 A sinusoidal voltage of peak value 293 V and frequency 50 Hz is applied to a series LCR circuit in which R 62 L 25 mH and C 750 F The impedance of the circuit is a 7 0 52 b 8 92 c 9 92 d 10 02

37 A circuit containing a 2022 resistor and 0 1 F capacitor in series is connected to 230 V ac supply of angular frequency 100 rad s The impedance of the circuit is a 10 c 10 2 b 10 2 d 10

a 7 0 2 b 8 92 c 9 92 d 10 02 7 A pure resistive circuit element X when connected to an ac supply of peak voltage 200 V gives a peak current of 5 A which is in phase with the voltage 54 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 90 If the series combination of X and Y is connected to the same supply what will be the rms value of current a 2 10 Sa A b A A C A d 5 A 8 An LCR series ac circuit is at resonance with 10 V 55 56

PPLIED TO A SERIES LCR CIRCUIT 35 In the circuit shown in figure what will be the reading of the voltmeter 100V 100 V rom I 200 V 100 Hz a 300 V c 200 V 36 In the series LCR circuit HH b 900 V d 400 V

27 A coil of inductance 1 H and negligible resistance is connected to a source of supply whose voltage is given by V 4 Volt If the voltage is applied at t 0 find the energy stored in the coil in 4 s a 512 J c 1024 J b 256 J play zigme d 144 J

9 In a series LCR circuit the voltage across an inductor capacitor and resistor are 20 V 20 V and 40 V respectively The phase difference between the applied voltage and the current in the circuit is a 30 b 45 c 60 d 0 1 When an ac source of voltage V V sin 100 is

In an L C circuit oscillations of energy E is sustained The capacitor plates are now slowly drawn apart to increase the oscillation frequency three times The work done in the process is nE Find n

c 1 294 27 Phase difference between voltage and current in a capacitor in an ac circuit is b x 2 a d 1 3 alternating current circuit consisting of c 0 a c 36 In

Ercuit 19 An ideal inductor is in turn put across 220 V 50 Hz and 220 V 100 Hz supplies The current flowing through it in the two cases will be a equal b different c zero incor d infinite 20 An inductor of 30 mH is connected to a 220 V ac source The induct

halved d zero 4 Which of the following graphs represents the correct variation of capacitive reactance X with frequencyu Xc a c xc U b d h U U a b c d 34 An V thr of t the a c

c d Only inductor A 30 F capacitor is connected to a 150 V 60 Hz ac supply The rms value of current in the circuit is a 17 A b 1 7 A c 1 7 mA d 2 7 A 160uF capacitor is connected to a 110 V rms 60 Hz 38 capaci of ang the cin a 10 c 10

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 AC VOLTAGE APPLIED TO A CAPACITOR 23 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 po 1 b c d 33 W ca a

2 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 AC VOLTAGE APPLIED TO A CAPACITOR by t 2 S 32 In w pow a b

21 Which of the following graphs represents the correct variation of inductive reactance X with frequency a c X D b d 29 200 31

30 A 60 F capacitor is connected to a 110 V rms 60 Hz ac supply The rms value of current in the circuit is a 1 49 A c 2 49 A b 14 9 A d 24 9 A c 38 A 0 in s of th a

vii An inductor with an inductance of 2 5H and a resistance of 802 is connected to the terminals of a battery with an EMF 6V and negligible internal resistance Find a The initial rate of increase of current in the circuit b The rate of increase of current at the instant when the current is 0 50A The current 0 25s after the circuit is closed The final steady state current c d

c SH SH d 7 H 3 H 91 Two inductors of inductance Leach are connected in series with opposite magnetic fluxes The resultant inductance is Ignore mutual inductance a zero b L c 2L d 3L

A two machine power system is shown below Transmission line xy has positive sequence impedance of z Q and zero sequence impedance of zo Q X Tel a phase to ground fault with zero fault impedance occurs at the centre of the transmission line Bus voltage at x and line current form X to F for the phase a are given by Va volts and la amperes respectively Then the impedance measured by the ground distance relay located at the terminal x of line xy will be given by

To 10 10 5 The root mean square value of voltage if an alternating safe va faxa e esinut ecosant fa voltage is given by e e sinet e cosmt is A B A B fote et e 1 2 2 e el 2 3 e ez 4 None of these e e 2 3 e e 4 er ega 2

II Reading in V is ahead in phase with reading in 1 III Readings in A and V are always in phase Which of these statements is are correct 1 I only 2 II only 3 I and II only 4 II and III only 3 A thin semicircular conducting ring PQR of radius r is falling with its plane vertical in a horizontal magnetic field B as shown in figure The potential difference developed across the ring when its speed is v is neet prep 3 Amp Amp 4 Amp Amp 5 The key K is inserted at time t 0 The initial 1 0 and final too currents through battery are 2V 100 ww K 1 Amp Amp 2 Amp Amp 2002 EMI AC EM waves live session 29 Aug Pag Contact Number 9667591930 8527521718 The velocity of light in this medium would be 1 2 5x 10 m s 213 108 m

32 For a domestic AC supply of 220 V at 50 cycles per second the potential difference between the terminals of a two pin electric outlet in a room is given by a V t 220 2 cos 100nt b V t 220 cos 50t c V t 220 cos 100nt d V t 220 2 cos 50

P Q R List l Qo HH Qo ww Initial charge on capacitor 0 60000000 www Initial current in inductor i List II Time constant is the time in 1 which current drops to 37 of its initial value Time constant is the time in 2 which current increases to 63 of its steady state value Time constant is the time in 3 which current increases to 37 of its steady state value

An ideal battery is connected to a resistor and an ideal inductor as shown Considering stead state A EMF across inductor is equal to emf across battery B Potential difference across inductor is equal to emf across inductor in magnitude C Potential difference across resistor is equal to emf across inductor in magnitude D EMF across resistor is zero 000000

A single circuit 60 Hz transmission line is 370 km or 230 mi long The conductor s outside diameter is 0 977in And the flat horizontal spacing is 7 25 m or 23 8 ft between conductors The resistance of the conductor is 0 1603 ohm mile The load on the line is 125MW at 215kV with 1 unity power factor a Find the voltage current and power at the sending end

In a pure capacitive circuit the current a lags behind the applied emf by angle 2 b leads the applied emf by an angle c leads the applied emf by angle 1 2 d and applied emfare in same phase

Alternating voltage is generated by rotating a coil in a normal magnetic field with 50 Hz frequency g If V 220V then the maximum flux passing rms through the coil is 1 0 99 Wb xxn 2 0 4 Wb 4 0 7 Wh

An uncharged capacitor of capacitances 12 0 uF is connected to a battery of emf 6 00 V and internal resistance 1 00 through resistanceless leads At 12 0 us after the connections are made i the current in the circuit is 1 4 42 A 2 6 A ii the power spent by the battery is 1 26 4 W 2 13 2 W iii the power dissipated in heat is 1 26 4 W 2 13 2 W 3 4 87 W iv the rate at which energy stored in the capacitor is increasing is 1 26 4 W 2 13 2 W 3 4 87 W 3 2 21 A 3 4 87 W 4 0 A 4 0 4 0 4 8 37 W

What is the value of inductance L for which the current is a maximum in a series LCR circuit with C 10 F and 1000s 1 10 mH 2 100mH 3 1 mH

V Two AC sources 1 10 sin wt V and 2 10sin wt v are fed to an LR circuit The resistance is R 100 and inductive reactance is X 10 3n The equivalent emf of the AC source has a peak value of 10 3V The peak value of current is 3 A 2 The voltage across the inductor at t The voltage across the resistor at t 3w 7T 3w IS is 15 3v 2 15 IS V R wwwww mwww LT

Q 37 A coil having a resistance of 7 ohms and an inductance of 31 8 mH is connected to 230 V 50 Hz supply Calculate i the circuit current ii phase angle iii power factor iv power consumed and v voltage drop across resistor and inductor Circuit current 16 85 A Phase angle 55 Power consumed 2484 24 W Voltage drops across R 200V Voltage drops across L 225 V Circuit current 15 85 A Phase angle 65 Power consumed 1484 24 W Voltage drops across R 131 95V Voltage drops across L 188 5 V Circuit current 14 85 A Phase angle 45 Power consumed 3484 24 W Voltage drops across R 131 95V Voltage drops across L 188 5 V Circuit current 18 85 A Phase angle 55 Power consumed 2484 24 W Voltage drops across R 131 95V Voltage drops across L 188 5 V

Q 34 A coil having a resistance of 7 ohms and an inductance of 31 8 mH is connected to 230 V 50 Hz supply Calculate i the circuit current ii phase angle iii power factor iv power consumed and v voltage drop across resistor and inductor Circuit current 16 85 A Phase angle 55 Power consumed 2484 24 W Voltage drops across R 200V Voltage drops across L 225 V Circuit current 15 85 A Phase angle 65 Power consumed 1484 24 W Voltage drops across R 131 95V Voltage drops across L 188 5 V Circuit current 14 85 A Phase angle 45 Power consumed 3484 24 W Voltage drops across R 131 95V Voltage drops across L 188 5 V Circuit current 18 85 A Phase angle 55 Power consumed 2484 24 W Voltage drops across R 131 95V Voltage drops across L 188 5 V

When the frequency of an ac circuit is decreased the current in the circuit increases The circuit is most likely to comprise of A resistance only B capacitor only sd C resistance and inductor D resistance and capacitor

3 A particle of mass 103 kg and charge 1 0 C is initially at rest At time t 0 the particle comes under the influence of an electric field E t Eo sin wt where Eo 1 0 N C 1 and w 10 rad s 1 Consider the effect of only the electrical force on the particle Then the maximum speed in m s 1 attained by the particle at subsequent times is

3 Calculate the r m s value the form factor and peak factor of a periodic voltage having the following values for equal time intervals changing suddenly from one value to the next 0 5 10 20 50 60 50 20 10 5 0 5 10 V etc What would be the r m s value of sine wave having the same peak value 60 50 20 10 5 10 20 50 60 Sine Wave

6 Consider the following series RLC circuit Here the symbols H L and C denote resistance inductance and capacitance respectively If frequency of the supply voltage is increased from a very low value to a very high value the maximum voltages across L and C are measured at frequencies fi and fc respectively Which of the following statements is correct a fc c fr 1 2 LC 1 and f and f 1 2 LC 1 b fo d fc 1 27 LC 1 and f and f 1 27 LC 1 G

In the figure an A C of 200 rms voltage is applied to the circuit containing diode and the capacitor and it is being rectified The potential across the capacitor C in steady state will be 1 500V 2 200V 283 V 4 141V Vo 200 52 Vo 20012 200V rms

In an n p n transistor 108 electrons enter the emitter in 10 8 s If 1 electrons are lost in the base the fraction of current that enters the collector and current amplification factor B are respectively Question Type Single Correct Type 1 0 8 and 49 2 0 9 and 90 3 0 7 and 50

If V 100sin 100t V and I 100sin 100t mA 3 are the instantaneous values of voltage and current then the rms values of voltage and current ar 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

The circuit shown in the figure has two sources connected in series The instantaneous voltage of the AC source in volts is given by v t 12 sin t If the circuit is in steady state then the rms value of the current in Ampere flowing in the circuit is v t 8 V 19 ww testbod 1H

In the figure shown V V V3 are AC voltmeters and A is AC ammeter The readings of V V V3 and A are 10 V 20 V 20 V 2 A respectively If the inductor is short circuited then the readings of v is m 5 volts Find m wir A V v 50Hz roro V3

A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns giving the output power at 230 V If the current in the primary of the transformer is 5 A and its efficiency is 90 the output current would be A B 50 A 45 A X

A series combination of an inductor L capacitor C and a resistor R is connected across an ac source of emf of peak value Eo and angular frequency w Plot a graph to show variation of impedance of the circuit with angular frequency w A square shaped current carrying loop MNOP is placed near a straight long current La com plane If the

The figure shows two sinusoidal curves representing oscillating supply voltage and current in an ac circuit O it T 4 E t Draw a phasor diagram to represent the current and supply voltage appropriately as phasors State the phase difference between the two quantities

by a AC source generating a square wave The output wave pattern monitored by CRO would look close to 1 2 R M CRO

passing through fine slits 14 Assertion Transformers are used only in alternating current source not in direct current Reason Only a c can be stepped up or down by means of transformers

F r given RC circuit Select the correct options Assume capacitor initially uncharged Maximum charge on capacitor is CE Current through resistor is E C Charge on capacitor at time t is CE 1 e RC Time constant of circuit is RC R at t 0 E