AC Circuits Questions and Answers

lllllllll An inductor has an inductance 25 mH 8 of these identical inductors are then connected in series This network of inductors is then connected to a 6 0 V cell of internal resistance 4 1 0 How much energy is stored within the magnetic fields of these inductors in total when the current has reached a steady value Express your answer in mJ

In an L C circuit shown in the figure C 1F L 4H At time t 4H At time t 0 charge in the capacitor is 4 Coulombs and it is decreasing at a rate of 5 Coulombs s The maximum charge in the capacitor is n Coulombs then value of n will be q F C

A constant electromotive force E volt is applied to circuit containing a constant resistance ohm in series with a constant inductance L henries If the initial current is zero What is t current in the circuit at any time 1 0 1 0 1 a 14 06 b E R di c L R E dt d Rag E dt C

Example A 50 kVA distribution transformer has iron loss of 600W and full load copper loss of 700W the transformer is supplying load The load cycle is as under 35HW and 0 8 power factor lag for 6 hours 30kW and 0 707 lag for 8 hours and no load for 10 hours Calculate the all day efficiency of the transformer

A 12 ohm resistor and a 0 21 henry inductor are connected in series to an AC source operating at 20 volts 50 cycle second The phase angle between the current and the source voltage is 3 80 V 4 90

Q40 As shown in figure a battery of emfs is connected to an inductor and resistance R in series The switch is closed at t 0 The total charge that flows from the battery between t 0 and r t t is the time constant of the circuit is O A EL eR O B ER eL O C EL R 1 1 e O D EL R R

A 3 phase 100 MVA 10 kV alternator has 5 reactance An external reactance Xseries per phase has to be connected in series with the alternator so that three phase short circuit does not exceed eight times the full load current The value of Xseries is 1 0 075 ohm phase 2 1 25 ohm phase 3 2 50 ohm phase

An inductive circuit contains resistance of 10 oh and an inductance of 20 H If an A C voltage 120 volt and frequency 60 Hz is applied to circuit the current would be nearly 2 0 16 amp 1 0 016 amp

A circular loop of radius r is made of a wire of circular cross section of diameter a When current I flows through the loop the magnetic flux linked with the loop due to self induced magnetic field is given by o Mor In 16r 7 I The resistivity of the material of a the wire is p and r a Switch S is closed at time t 0 so as to connect the loop to a cell of emf V Find the current in the loop at time t S

Two resistors are connected a in series b in parallel The equivalent resistance in the two cases is 9 ohm and 2 ohms respectively Then the resistances of the component resistors are 1 2 ohm and 7 ohm 2 3 ohm and 6 ohm 3 3 ohm and 9 ohm 4 5 ohm and 4 ohm

No 37 View In English A capacitor of capacitance C has initial charge Og and connected to inductor L as shown at t 0 switch S is pressed The current through the inductor when onergy in the capacitor is three times of the onergy of the inductor in 10 2 3 4 Correct Answer 1 2VLC Qo 200 VLC 40 VLC D

Part a of the drawing shows a resistor and a charged capacitor wired in series When the switch is closed the capacitor discharges as charge moves from one plate to the other Part b shows the amount q of charge remaining on each plate of the capacitor as a function of time In part c of the drawing the switch has been removed and an ac generator has been inserted into the circuit The circuit elements in the drawing have the following values R 14 00 Vrms 24 0 V for the generator and f 385 Hz for the generator The time constant for the circuit in part a is 7 3x104s What is the rms current in the circuit in part c R ww a C Switch 9 b R www c C

A circuit containing an inductance and a resistance connected in series has an AC source of 200 V 50 Hz connected across it An AC current of 10 A ms flows through the circuit and the power loss is measured to be 1kW 3 10x B The frequency of the AC when the phase difference between the current and emf 50 becomes 1 4 with the above components is Hz A The inductance of the circuit is H C The frequency of AC at which the reactive power is half of the actual power loss 25 is Hz D The frequency of the AC when the phase difference between the current and emf 25 becomes 1 4 with the above components is 3 Hz

0 Energy in a typical inductor a How much energy is stored in a 9 20 mH inductor carrying a 1 25 A current b How much current would such an inductor have to carry to store 1 4 J of energy Is this a reasonable amount of current for ordinary laboratory circuit ele ments

What is the resonant frequency for the circuit below assuming that the RMS value of Vs 100 V the operating frequency is 169 kHz C R w HH 470 2 330 H 2000 pF Vs 196 kHz 169 kHz Else 961 kHz L m m

Consider a stator winding of an alternator with an internal high resistance ground fault The currents under the fault condition are as shown in the figure The winding is protected using a differential current scheme with current transformers of ratio 400 5 A as shown The current through the operating coils is CT ratio 400 5 m 220 j0 A 250 j0 A let CT ratio 400 5 Operating coil

of the voltmeter ww 1 300 V 2 900 3 200 4 400 V 1 0V 34 2 1501 34 3 1501 64 4 0V 84 10 In the circuit shown in figure neglecting source resistance the voltmeter and ammeter reading will respectively will be R 3002 2 12 100V moooooo 100V 200V 100 Hz vvvvvvv X 2502 X 2502 11 0 An ac source of angular frequency is fed across a resistor r and a capacitor C in series The current registered is 1 If now the frequency of the source is changed to co 3 but maintaining the same voltage the current in the circuit is found to be halved Calculate the ratio of reactance to resistance at the original frequency 00 240 V For a series RLC circuit R XL 2Xc The impedance of the circuit and phase difference between V and i will be 1 VR tan 2 2 tan 3 5Xc ta 2 4 5R tan 1 13 In the adjoining ac circuit the voltmeter whose reading will be zero at resonance is 0000000 L 1 V 2 V 3 V 3 14 A constant voltage at different frequencies is applied across a capacitance C as shown in the figure Which of the following graphs Signal Generator 1 V ww R V Correctly depicts the variation of current with frequency k 0

In the equivalent circuit of three phase induction motor the mechanical loa the motor can be represented by a resistance of value R2 rotor resistance s slip OR2 1 s OR2 1 s s R2 1 s

1 An ac source of angular frequency is fed across a resistor r and a capacitor C in series The current registered is 1 If now the frequency of the source is changed to 3 but maintaining the same voltage the current in the circuit is found to be halved Calculate the ratio of reactance to resistance at the original frequency 0 2 7 3 2 neet prep k 3 20 0 across a capacitance as shown in the figure Which of the following graphs Signal Generator Correctly depicts the variation of current with frequency K 1 2 V Mini Test 21 Different Types of AC Circuits Contact Number 9667591930 8527521718 3 current 1 t leads voltage V t by 180 4 current 1 t lags voltage V t by 90 18 1 P 2 P 3 P 4 4 P 19 Page A resistance R draws power P when connected to an AC source If an inductance is now placed in series with the resistance such that the impedance of the circuit becomes Z the power drawn will be

any energy from the voltage source 2 current I t is in phase with voltage V t neet prep inductor of reactance 311 The impendance of the is z Now a capacitor of reactance 69 Mini Test 21 Different Types of AC Circuits Contact Number 9667591930 852752 is connected in the series of above combination the impedance becomes 22 Then will be 1 1 1 1 2 3 B 2R E L 212 E L R

Example 14 4 The V I characteristic of a silicon diode is shown in the Fig 14 17 Calculate the resistance of the diode at a I 15 mA and b Vp 10 V 10 V 30 20 150 10 I mA 1 A 0 5 0 8 Silicon V V

In an L R circuit AC source of frequency 50 Hz is connected as shown in the figure The phase difference between voltage and current is 1 90 3 45 R 157 Q L 2 3 H wwwm 50 Hz 2 60 4 30

72 A capacitor stores 60 C charge when connected across a battery When the gap between the plates is filled with a dielectric a charge of 120 c flows through the battery The dielectric constant of the material inserted is a 1 c 3 b 2 d 4 72 A chorced capacitor is allowed to discharge through

In the circuit shown resistance 10032 2 inductance L H and capacitance 3 C F are connected in series with an ac source of 200 volt and frequency f If the reading of the hot wire voltmeter V and V are then which is incorrect

1 2 3 positive negative and zero sequence impedances are equal positive and negative sequence impedances are equal zero and positive sequence impedances are equal negative and zero sequence

A surge of 100 kV travels along an overhead line towards its junction with a cable The surge impedance for the overhead line and cable are 4000 and 50 respectively The magnitude of the surge transmitted through cable is in kV

R 100 C L 100 100 T F L mH are connected to an ac and T source as shown in the figure The rms value of ac calue is 220 V and its frequency is 50 Hz In List 1 some physical quantities are mentioned while in List 2 information about quantities are provided Match the entries of List 1 with the entries of List 2 www m R C

resistance is connected to an A C source of 200 V and angular frequency 300rads When only the capacitor is removed the current lags behind the voltage by 600 When only inductor is removed the current leads the voltage by 60 If all clamor otod the

When an ac source of voltage V Vo sin100t is connected across a circuit the phase difference between the voltage V and current I in the circuit is observed to be 4 as shown in figure If the circuit consists possibly only of RC or RL or LC in series find possible values of two elements A and V V TE X t s

b In the R L circuit shown in the below figure the resistance R 30 ohm and reactance X 40 ohm and peak e m f V 220 V Calculate i Impedance Z ii phase difference between e m f and current L oooo R w VAC 2

An AC source of emf 5 0 V is connected to a series RLC circuit at a phase angle of 33 Find the potential difference across the capacitor when the magnitude of potential difference across the inductor reaches the maximum value of 6 0 V a 6 9 V b 2 9 V c 12 8 V d 33 V

In order to avoid eddy currents in the core of a transformer O The number of turns in the secondary coil is made considerably large OA laminated core is used A step down transformer is used A high voltage alternating weak current is used

The series combination of resistance R and inductance L is connected to an alternating source of emf e 311 sin 100 t If the value of wattless current is 0 5 A and the impedance of the circuit is 311 the power factor will be Question Type Single Correct Type 1 1 2 2 3 1 2 S

An AC source rated 220 V 50 Hz is connected to a resistor The time taken by the current to change from its maximum to the rms value is mathongo mathongo mathongo mathongo mathongo 1 2 5 ms mathongo mathongo 2 25 ms 3 2 5 songo mathongo SAYO Or mathango mothonge mathange mathonge mathango mathonge

In a series LCR circuit the inductive reactance X is 1002 and the capacitive reactance Xc is 42 The resistance R in the circuit is 652 The power factor of the circuit is thongs mathongo mathongamathongs mathongo DE 2 3 IN 12 15 22 thongs mathongo mathongo mathongo mathongo mathongo mathongamathanga mathongo mathongo

A sinusoidal voltage of peak value 250 V is applied to a series LCR circuit in which R 80 L 24mH and C 60 F The value of power dissipated at resonant condition is x kW The value of x to the nearest integer

The variation of EMF with time for four types of generators are shown in the figures Which amongst them can be called AC NEET 2019 Odisha EA a c EA EA 1 Only a 3 a b c d t b d EA 2 a and d 4 a and b t

A generator with constant 1 0 p u terminal voltage supplies power through a step up transformer of 0 12 p u reactance and a double circuit line to an infinite bus bar as shown in the figure The infinite bus voltage is maintained at 1 0 p u Neglecting the resistance and susceptances of the system the steady state stability power limit of the system is 6 25 pu If one of the double circuit is tripped the resulting steady state stability power limit in p u will be 1 2 X 3

For a power system the admittance and impedance matrices for the fault studies are as follows Ybus j8 75 j1 25 j2 50 j1 25 j6 25 j2 50 j2 50 j2 50 5 00 Zbus j0 16 j0 08 j0 12 j0 08 j0 24 j0 16 Lj0 12 j0 16 j0 34 The pre fault voltages are 1 0 p u at all buses The system was unloaded prior to the fault A solid 3 phase fault takes place at bus 2 The post fault voltages at buses 1 and 3 in per unit respectively are

consider two buses connected by an impedance of 0 5j The bus 1 voltage is 100 230 V and bus 2 voltage is 100 20 V The real and reactive power supplied by bus 1 respectively are 1 1000 W 268 VAr 2 1000 W 134 VAr 3 276 9 W 56 7 VAr 4 276 9 W 56 7 VAr

A 2 bus system and corresponding zero sequence network are shown in the figure Bus 1 T Bus 2 XGn 3X Gr XOG T leeee XOT1 leeee XOL a XOT2 XOM A 3XMn Mn b The transformers T and To are connected as

An RLC series circuit is driven by a sinusoidal emf with angular frequency o If is increased without changing the amplitude of the emf the current amplitude increases It means 1 L 1 wC 1 2 wL 3 19 wC

An ideal choke takes a current of 8A when connected to an a c source of 100 volt and 50 Hz A pure resistor under the same conditions takes a current of 10A If two are connected in series to an a c supply of 100V and 40 Hz then the current in the series combination of above resistor and inductor is A 10A B 8A C 5 2 amp P 19 2 amp

Consider the LR circuit shown in the figure If the switch S is closed at t 0 then the amount of charge that passes through the battery between t 0 and t A B L 0000 E EL 2 7R L R EL 7 3R is R www Lou

In a series sinusoidally driven LCR AC circuit the current lags the applied emf The rate at which energy is dissipated in the resistor can be increased by 1 Decreasing the capacitance and making no other change 2 Increasing the capacitance and making no other change 3 Increasing the inductance and making no other change 4 Increasing the driving frequency and making no ong

In the circuit shown the switch 1 is closed first and then switch 2 is closed The amount of heat developed in resistance R will be 1 R wwww LE 18R E 1 S 12 www 2R R 2 L 000 www LE 27R 2R

instant comes out volt value of N is N 3 s 1 A and peak value of current is 3 potential difference between P and Q at the same P R 32 X 49 wwwmooooo 5 Q A The

The net resistance of a voltmeter should be large to ensure that a It does not get overheated b It does not draw excessive current c It can measure large potential difference d It does not appreciably change the potential difference to be measure email com ta

a Draw graphs showing the variations of inductive reactance and capacitive reactance with frequency of the applied ac source b Draw the phasor diagram for a series RC circuit connected to an ac source c An alternating voltage of 220 V is applied across a device X a current of 0 25 A flows which lag behind the applied voltage in phase by radian If the same voltage is applied across another device Y the same current flows but now it is in phase with the applied voltage i Name the devices X and Y ii Calculate the current flowing in the circuit when the same voltage is applied across the series combination of X and Y

30 An LC circuit contains a 20 mH inductor and a 50 F capacitor with an initial charge of 10 mC The resistance of the circuit is negligible Let the instant at which the circuit which is closed be t 0 At what time the energy stored is completel magnetic a t 0 c t 3 14 ms b t 1 57 ms d t 6 28 ms