AC Circuits Questions and Answers

Two identical unloaded generators are connected in parallel as shown in the figure Both the generators are having positive negative and zero sequence impedances of j0 4 p u j0 3 p u and j0 15 p u respectively If the pre fault voltage is 1 p u for a line to ground L G fault at the terminals of the generators the fault current in p u is

The RL circuit of the figure is fed from a constant magnitude variable frequency sinusoidal voltage source Vin At 100 Hz the R and L elements each have a voltage drop HRMS If the frequency of the source is changed to 50 Hz then new voltage drop across Ris Vin R www testboo

The current flowing in the AC source shown in th circuit in ampere is L H 5 vooooo 500 C uF wwww 102 100 2 sin 100nt V 1 30 2 sin100nt A T 2 30 2 sin 100nt 4 T I 3 10 2 sin 100 t 4 A A

An RLC series circuit has a voltage source given by E t 30 V a resistor of 120 02 an inductor of 6 H and a capacitor of 0 01 F If the initial current is zero and th initial charge on the capacitor is 4 C determine the current in the circuit for 1 0 Type an exact answer using radicals as needed

Ques 2 A coil of resistance 10 2 and L 0 1 m H is connected in series with a capacitor of 150 F across 200V 50 Hz supply Determine XL Xc Z Current and Voltage across inductor and capacitor power factor ICC DIT

The line currents of a three phase four wire system are square waves with amplitude of 100 A These three currents are phase shifted by 120 with respect to each other The rms value of neutral current is

For transistor action 1 Base emitter and collector regions should have similar size and doping concentrations 2 The base region must be very thin and lightly doped 3 The eimtter base junction is forward biased and base collector junction is reverse based 4 Both the emitter base junction as well as the base collector junction are forward biased 2010 a 3 4 c 1 2 b 4 1 d 6 86

2 A 4uF capacitor a resistance of 2 5 m2 is in series with 12 V battery Find the the time after which the potential difference across the capacitor is 3 times the potential difference across the resistor Given In 2 0 693 a 13 86 s b 6 93 s

A square wave current switching rapidly between 1 0 A and 1 0 A with period of 0 2 s is passed through an AC ammeter The reading of ammeter is 1 0 A 1 2 2 0 A hr min 2 A

Column I a Resonant frequency b Quality factor c Average power d Impedance e Magnetic potential energy f Coefficient of self induction Column II i VI cos ii LI iii iv R XL Xc v 1 LC vi E at dt wo L R

In a L C R circuit capacitance is changed from C to 2C For the resonant frequency to remain unchanged the inductance should be change from L to Question Type Single Correct Type 1 4 L 2 2L 3 L 2

the source Voltage leads circuit current at known frequency f If f is lowered slightly the circuit impedance will 1 Increase 2 Decrease 3 Remain same 4 Need to know whether the phase angle is less than 45 or greater than 45

The current I time t according to the graph given below Which one of the following graphs gives the variation of voltage in the coil with time 1994 A B C D V t V A t V Ho V

In case of phase lag compensation used in system gain cross over frequency band width and undamped frequency are respectively 1 decreased decreased decreased 2 increased increased increased 3 increased increased decreased 4 increased decreased decreased

The equation of emf in an ac circuit is given by E 200 2 sin 200rt volt what is the minimum time taken for the emf to change from 200 V to 200 V 200 a 1 100 Icl 100s E b 200s d 1 200 s

A town situated 20 km away from a power plant generating power at 440 V requires 600 kW of electric power at 200 V The resistance of the two wire line carrying power is 0 42 per km The town gets power from the line through a 3000 220 V step down transformer at a substation in the town i Find the line power losses in the form of heat ii How much power must the plant supply assuming there is negligible power loss due to leakage CBSE OD 03 19 CAO LIAZ

A common emitter amplifier has a voltage gain of 50 an input impedance of 10002 and an output impedance of 2002 The power gain of the amplifier is a 500 2010 c 1250 b 1000 d 50

OF The peak value of an alternating emf E given by E E cos oot is 10 V and its frequency is 50 Hz At a time t s the instantaneous value of the emf is 100 a 10 V c 5V The power loss in AC ci EET b 5 3 v d 1V it will be minimum when

single strand The self inductance of a choke coil is 10 mH When it is conected with a 10V D C source then the los of power is 20 watt When it is connected with 10 volt A C source loss of power is 10 watt Th frequency of A C source will be RPMT 1995 1 50 Hz 2 60 Hz 3 80 Hz 4 100 Hz If the frequency of the source e m f in an AC circuit is n the power varies with a frequency

ag ti An a 20 mH inductor and a 50 uF capacitor with an initial charge of 10 mC The resistance of the circuit is negligible this is som Let the instant the circuit is closed be t 0 le at a What is the total energy stored initially Is it conserved during LC oscillations b What is the natural frequency of the circuit c At what time is the energy stored I T Y completely electrical i e stored in the capacitor ii completely magnetic i e stored in the inductor 18 d At what times is the total energy shared equally between the inductor and the capacitor a resistor is inserted in the circuit how much energy is eventually dissipated as heat A coil of inductance 0 50 H and resistance 100 2 is connected to a 240 V 50 Hz ac supply imum current in the coil oltage maximum and the

The battery shown in figure is ideal The values are 10 V R 502L 2H current through the battery at t 2sect 1 Initially the current in the inductor is zero The is 2102 in Ampere Find Io Inductor is ideal EL

A cone rolls without slipping on the horizontal surface so that its apex remains fixed and the axis of once is horizontal The radius of base of cone is 1 and the semi vertex angle is a The centre of bas of cone is C and it moves with constant speed vo Find the speed of point A and point B relative to surface ACB 90 Point A and B lies on circumference of the base of cone A 2v V 2 tan c B V V 2 tan a C 2V Vo 1 tan a 24 Front View

A solenoid has an inductance of 20H and a resistance of 40 It is connected to a 20V battery How long will it take for the magnetic energy to reach 1 9th of its maximum value A 5ln 3 2 B 5ln 2

Juctor in Figur ding all insulated metal wire around a core of soft magnetic material ferrite The cylindrical coil has 9 turns a length of 458 mm and a diameter of 16 mm The core has a relative permeability of 325 and negligible resistance End Y End X iii iv End P Oll Figure Q1a A cylindrical coil inductor At t 0 s the student completes a series circuit by connecting end X of the wire to the positive terminal of a power supply and end Y to a 10 2 resistor that was connected to the negative terminal of the supply The power supply has an emf of 12 V and a negligible internal resistance i i ii iii End Q a i Show that the inductance of this inductor is approximately 15 H Calculate the time constant of this LR circuit ii Calculate the current in the circuit at time t 3 us Calculate the time taken for the current in the circuit to reach 1 1 A The student leaves the inductor connected to the power supply until the current reaches a steady value b Calculate the magnitude of the magnetic field strength inside the inductor Which end P or Q of the inductor is the North pole State the name of the rule you have used to determine this How much magnetic flux is coming out of the North pole of the inductor Calculate the amount of energy stored within the magnetic field of the inductor The student now places the inductor and the 10 resistor in series with a 180 nF capacitor and an 80 kHz AC power supply of negligible internal resistance c Calculate the capacitive reactance the inductive reactance the impedance and the phase angle for this LCR circuit and hence draw a fully labelled phasor diagram showing all of these values Finally the student removes the AC power supply and uses the series inductor and capacitor combination from part c within a radio receiver circuit d Calculate the wavelength of the radio signal that this circuit will pick up 11 5 6 3

In the given A C circuit the r m s voltage of the source is 60 V then the r m s current passing through the source is 10 x A then the value of x is X 352 oooooooo 4 X 30 C 2 R 592 wwww Xc 192 X 792 H1 mmmmmmm C L

A 150 F capacitor in series with a 1502 resistance is connected to a 200 V 50 Hz supply a Determine the average power dissipated per cycle of the AC b Determine the current amplitude in the circuit c Determine the time lag between the current maximum and the voltage maximum d Determine the impedance of the circuit n of

The circuit shown consists of a switch S a battery B of emf E a resistance R and an inductor L B S A E R C The current in the circuit at the instant the switch is closed is www R B E R 1 e L

In the network given the switch is closed at t 0 s Determine the time constant 7 voltage across the inductor v and current it at t O s 4 marks E 8V R 2 2 km R 4 7 kn ele 10 mH UL

An ac generator has a frequency of 2 2 kHz and a voltage of 240 V An inductance L 5 0 mH is connected across its terminals Then a second inductance L 10 mH is connected in parallel with L Find a the current that the generator delivers to L and b to the parallel combination a i

An ideal resistance R ideal inductance L ideal capacitance C and AC volt meters V V2 V3 and V4 are connected to an AC source as shown At resonance A B R V V4 L 0000 V 2 C V3 Reading in V3 reading in V Reading in V reading in V

D A circuit when connected to an AC source of 12 V gives a current of 0 2 A The same circuit when connected to a DC source of 12 V gives a current of 0 4 A The circuit is b series RC a series LR c series LC d series LCR Odisha NEET 2019 reduces at a 0 05 s If th the total d during thi a 16 C c 16m

In a series LCR circuit the voltage across R is 100 V and R 1 k2 C 2 F The resonant angular frequency w is 200 rad s 1 Lis A B C At resonance the voltage across 40V 250V 4 x 10 V D 2 5 10 V Correct Answer

The switch in the circuit shown shifts from 1 to 2 when 2V Vc 3 V and goes back to 1 from 2 when Vc 3 This process is repeated several times The variation in reading of voltmeter with respect to time is as plotted The period T of the wave form in terms of R and C will be Assume resistance of voltmeter to be equal to R Thr V 2V13 V13 RCIn3

how much energy is dissipated as heat A coil of inductance 0 50 H and resistance 1000 is connected to a 240 V 50 Hz ac supply What is the maximum current in the coil b What is the time lag between the voltage maximum and the current maximum 7 13 if the circuit is

A single phase 22 kVA 2200 V 220 V 50 Hz distribution transformer is to be connected as an auto transformer to get an output voltage of 2420 V Its maximum kVA rating as an auto transformer is 1 2 22 24 2 3 242 2100

6 For the source free parallel RLC circuit R 60 L 7H and C 0 023F Calculate the damping constant and natural frequency Is the natural response overdamped underdamped or critically damped 2 marks

A coil of inductive reactance 1 30 and resistance 1 is connected to 200V 50Hz A C supply The time lag between maximum voltage and current is A B C 1 600 S 1 200 1 S S 300 Correct Answer

2 An alternating current generator has an internal resistance R and an internal reactance X It is used to supply power to a passive load consisting of a resistance R and a reactance X For maximum power to be delivered from the generator to the load the value of X is equal to a Zero c Xg Wh b Xg d R g

3 Assertion Series LCR circuit is a voltage magnifier Reason In series LCR circuit at resonance voltage drop across inductance or capacitance is Q quality factor times the applied voltage

When a voltage measuring device is connected to AC mains the meter shows the steady input voltage of 220 V This means a Input voltage cannot be AC voltage but a DC voltage Maximum input voltage is 220 V e The meter reads not v but y and is calibrated to read d The pointer of the meter is stuck by some mechanical defect

13 Assertion At resonance the inductive reactance is equal and opposite to the capacitive reactance Reason In series LCR circuit the inductive reactance is equal and opposite to the capacitive reactance

Q9 a What do you understand by Q factor in series LCR circuit b Explain how it depends the values of L C R c For better selectivity a series LCR circuit for larger bandwidth or smaller bandwidth is preferred Q10 An RLC circuit consists of a resistance of 1000W an inductance of 100 mH and a capacitance of 10uF The Q factor of the circuit is

36 00 20 B A 12 resistor and a 0 21 H inductor are connected in series to an a c source operating at 20 v 50 cycles second The phase angle between current and source voltage is 30 G 40 C 50 ene 4 Your Answer 3 Correct Answer

A capacitor consists of two metal plates each 500 x 500 mm and spaced 6 mm apart The space between the metal plates is filled with a glass plate of 4 mm thickness and a layer of paper of 2 mm thickness The relative perimitivities of the glass and paper are 8 and 2 respectively Neglecting the fringing effect the capacitance will be Given that 8 85 x 10 12 F m

2 F 8 F A capacitor of 2uF is charged as shown in the diagram When the switch S is turned to position 2 the percentage of its stored energy dissipated is 2 20 1 0 3 75 80

View In English A small metallic ball is charged positively and negatively in a sinusoidal manner at a frequency of 108 cps The maximum charge on the ball is 108 C What is the maximum displacement current due to this alternating current EWEE rect Answer 1 6 28 amp 3 4 amp 3 75 10 4 amp 12 56 amp

Q 84 Two conducting sphere of radius R are placed at a large distance from each other They are connected by a coil of inductance L as shown in the figure Neglect the resis tance of the coil The sphere A is given a charge Q and the switch S is closed at time t 0 Find charge on sphere B as a function of time At what time charge on B is A R L 00000 S B R

5 A battery is charged at a potential of 15 V for 8 hours when the current flowing is 10 A The battery on discharge supplies a current of 5 A for 15 hours The mean terminal voltage during the discharge is 14 V The Watt hour efficiency a the battery is 1 300 2 90 3 87 5 4 80 F

3 In the circuit shown below the Zener diode is used to regulate the voltage across the load R 500 22 For an unregulated power supply V of 12 V the voltage across the load is to be maintained at 8 V If the resistor R has a value of 100 S2 the current through the Zener diode is S 12 V R 100 92 A 16 mA B 24 mA C 40 mA www ww R 500 92

A zener diode is operating in its normal region i e the breakdown region for which the circuit diagram is as shown in the figure ET B A R www Vz A A Here take Vz 7V and R 10kn For potential difference equal to 8 V across AB what is the current through microammeter