AC Circuits Questions and Answers

Take g 10 m s a 0 b 30 d 90 A fully charged capacitor C with initial charge o 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 field is a LC JIC b d 2n IC NLC ectrum the one

7 In the given circuit the potential difference across resistance is 80 V and power consumed by it is 160 W If AC frequency is 50 Hz find the value of L 100V 50Hz 1 0 3 H 3 10 H www 2 4 eeeeee L 0 3 H 0 7 H

In the following transistor amplifier circuit B 50 VCE of the transistor is 245kQ 40 AY B 10 V 2ks

An electron moves along vertical line and towards observer the pattern of concentric circular field lines of magnetic field which is produced due to its motion 1 ACW In horizontal plane 3 CW In horizontal plane 16 12 2 ACW In vertical plane 4 CW In vertical plane

In given circuit applied voltage V 50 2 sin 100m volt and mmeter reading is 2A then calculate value of

In the shown circuit the rms current through source i will be A 4A C 5A B 15 A D 7A i L L 0 125H ic C 1 4mF R R 12 5Q

List I contains different AC circuits with rms voltage of ac sources as shown List II contains the mms currents supplied by the ac voltage sources Then match the options of List I corresponding correctly with the options of List II LIST I LIST II P R S wwwww X Xc 4Q 100 V X www Xc 30 R 80 www 120 V 18888000 X 562 Xc 30 50 V www X 8Q Xc 40 100 V ww R 30 wwww R 80 ww R 802 www R 30 6 26 yo 4 37 to 1 2 3 4 I 25 A Ims 5 A Im 10 5 A Im 20 A

12 The average electromagnetic 1 EH value of poynting vector in wave is 2 4 E Ho 2 E Ho

In the figure shown V b at t 1 s is ab 2H a 1 30 V 202 2F b 4V www1100000 1 q 4t C 2 30 V 3 20 V 4 2 res

ng emf E E cos 100 m st cos500 m st S is connected in series with a capacitor and a resistor The steady state current in the circuit is found to be i i cos 100 r s t 9 i cos 500 m st i i b i i c i i a i i d The information is insufficient to find the relation between i and i 2 An AC so

A series LCR circuit contains a 50 resistance 2H inductane and F capacitance 800 19T T connected across a 220V 50Hz ac source The net reactance of the circuit is 1 2000 2 237 5 3 3750 AY

In an LCR circuit capacitance is changed from C to 2C For the resonant frequency to remain unchanged the inductance should be changed from L to 1 4L 3 L 2 2 2L 4 L 4

2 1 5 3 19 13 The combination of NOR gates shown here is equivalent to 1 OR B 2 AND 3 NAND 4 19 1 4 XOR of different fr

0 An AC voltage e eo sin 50t e cos 100mt is connected in series with a resistor and capacitor The steady state current through circuit is found to be 1 lo sin 50nt o lo cos 100nt 10 lo Then the ratio of a greater than 1 c less than 1 is b equal to 1 d None of these

34 A sinusoidal voltage of peak value 200 volt is connected to a diode and resistor R in the circuit shown so that half wave rectification occurs If the forward resistance of the diode is negligible compared to R then the rms voltage involt across R is approximately 8 200 Volt 200

10 If instantaneous current in a circuit is given by 2 3 sin wt A then the effective value of resulting current in the circuit is 1 3 17 2 3 2 A A 2 V17 4 3 2 A 2 A

4 When alternating current flows through a conductor the rate of flux change 1 Is higher in the inner part of the conductor 2 Is lower in the inner part of the conductor 3 Is uniform throughout the conductor 4 Depends on the resistivity of the conductor

An ideal inductor is in turn put across 220 V 50 Hz and 220 V 100 Hz supply The current flowing through it in two cases will be More in first case More in second case Equal in both cases Zero in first and infinite in second

11 An LCR circuit is equivalent to a damped pendulum In an LCR circuit the capacitor is charged to Qo and then connected to the L and R as shown below a R www If a student plots graphs of the square of maximum charge QMax on the capacitor with time t for two different values L and L L L of L then which of the following represents this graph correctly plots are schematic and not drawn to scale QMax L vooor b 2 Qax Qo For both L and L

An AC source of angular frequency o is connected with a resistance R and an uncharged capacitance C in series The potential difference across the resistor is in phase with the initial potential difference across the capacitor for the first time at the instant assume that at t 0 emf is zero G 2n TU 200

10 In an A C circuit maximum voltage and maximum currents are 220 V and 4 4 A respectively Calculate power and power factor in the circuit Here X 30 2 and R 40 2 Ans 387 2 W 0 8 11 In an A C circuit R and L are connected in series with source of maximum 220 V and frequency 50 Hz If L 1 H and R 100 22 Find the maximum current in inductor and phase difference between voltage and current Ans 0 668 A 72 20

5 In an ideal transformer input A C voltage is 220 V Current in secondary coil is 2 5 A If the ratio of number of turns in primary coil and secondary coil is 1 10 find 1 Output voltage 2 Current in primary coil 3 Input and output power Ans 2200 V 25 A 5500 WI

The phase difference between current and voltage in an AC circuit is radian If the frequency of the AC used is 50 Hz then the phase difference is equivalent to the time difference O 0 78 ms 0 7 8 ms O 0 25 ms O 2 5 ms 7 4

A bulb and a capacitor are connected in series to a source of alternating current If its frequency is increased while keeping the voltage of the source constant then O bulb will give more intense light O bulb will give light of same intensity as before O bulb will give less intense light O bulb will stop radiating light

The phase difference between current and voltage in an AC T circuit is radian If the frequency of the AC used is 50 Hz 4 then the phase difference is equivalent to the time difference 0 78 ms O 7 8 ms 0 25 ms 2 5 ms

Question No 17 In an LCR series circuit R 10 Q XL 20 0 and Xc 10 0 The average value of current for a complete cycle source voltage V 20 sin 301 is 2 A 0 5 A 3 A Zero

75 For a series LCR circuit quality factor is o and potential difference across circuit is B The potential difference across inductor in resonance state will be 1 Zero 2 ap 3 2 8 a

35 In the given circuit switch is clos After a long time the iron rod is withdrawn from the inductor L Then the bulb Iron Rod 70000 L tham S B 1 Glows with same brightness 2 Glows more brightly 3 Gets dimmer 4 Stops glowing R

35 The current through a wire changes with time according to the equation I The correct value of the rms current within the time interval t 2 to t 4s will be A 3 A C 5 A B 3 A D None of these

Calculate the active and reactive components of current in each phase of a star connected 10 000 volts 3 phase generator supplying 5 000 kW at a lagging p f of 0 8 Select one a 288 A 216 A b 350A 290A c 410A 370A d 210A 156A

A supply voltage of 230 V 50 Hz is fed to a residential building Write down its equation for instantaneous value Select one a 163 sin 314 16t O b 325 sin 314 16t O c 230 sin 314 16t d 360 sin 314 16t

Three identical coils connected in delta to a 400V 3 phase supply take a total power of 50kW and a line current of 90 A Find phase current and power factor Select one O a 52A 0 80 O b 35A 0 80 O c 40A 0 80 Od 66A 0 90

An inductor 20 10 3 henry a capacitor 100 F and a resistor 500 are connected in series across a source of EMF V 10 sin 314t If resistance is removed from the circuit and the value of induc tance is doubled then the variation of current with time in the new circuit is 2014 a 0 52 cos 314 t c b 0 52 sin 314t 052 sin 314t 7 3 d None of these

A direct current of 5A is superposed on an alternating current I 10 sin oot flowing through the wire The effective value of the resulting current will be 2015 a 15 2 A c 5 5A 5 3A b d 15 A

This section contains 35 SINGLE COR 20 Q An AC circuit has an inductive reactance equal to 10 Q and a resistance of 100 The effective impedance of the circuit is O 10 2 22 Read More O 10 3 2 questions Each question has 4

14 In the circuit shown the switch S closed for a long time The switch is now opened so that the capacitor gets charged 50 kQ www OV 1 S A Infinite B 1 5s C 1s D 0 67s 10 F 100 k The time constant of the circuit is

T 10 J 2 2 106 J 3 3 106 J 4 4 A charged capacitor is connected with a resistor After how many time constants does the energy of capacitor become 1 10th of its initial value AIIMS 2014 4 2 3 2 1 15 3 0 69 4 none of these with air as a dielectric has capacitance C A slab of dielectric constant K having s in the fir

An AC circuit consists of a 2200 resistance and a 0 7 14 choke Find the impedance of the coat when the resistance and the choice are in series and are connected to a 220 V and 50 Hz source O Click here to view this option tef No 241401 O O D Click here to view this option et No 211401 Click here to view this option set 241401 Click here to view this option et No 241401

Ques 5 A constant electromotive force E volts is applied to a circuit containing a constant resistance R ohms in series and a constant inductance L henries If the initial current is zero show that the current builds up to half its theoretical maximum in L log2 R seconds

The mutual induction between primary an secondary coils of a transformer is 2 H If an A current of peak value 5 A and frequency 50 H flows through the primary coil then the pea voltage in secondary coil is 2 10 volts 4 20 volts 1 10 volts 3 1000 volts

and Three resistors having resistances r r2 r3 are connected as shown in the given circuit The iz ratio of currents in terms of resistances used 11 in the circuit is A i 1 3 r1 www r1 12 13 i2 r2 ww www 2 Deq 82B 03 0 83 82 r2 12 13 L901802 r1 r r2 rep B r t 3283 2 2

16 An alternating emf of frequency v 2 LC is applied to a series L C R circuit For the frequency of the applied emf 1 the circuit is at resonance and its impedance is made up only of a reactive part 2 The current in the circuit is in phase with the applied emf and voltage across R equals the applied emf 3 the sum of the potential difference across the inductance and capacitance equals the applied emf which is 180 ahead of phase of the current in the circuit 4 the quality factor of the circuit is 1 CR 16 faza fauc arafu v OL R or and this is measure of the voltage magnification produced by the circuit at L C R enginfor 1 t 2 a ft RIGH fan fav 3 du fawaink an die T 180 4 factual que CL R 2x LC all CR TEE he

current phasor I is V 1 2 V sin oot L i sin oot m V sin oot m i sin wt 2 m wt TC 2 Soot behind the voltage phasor V 3 Both 1 and 2 4 Neither 1 nor 2

2 In an L R C series circuit the rms voltage across the resistor is 30 0 V acros the capacitor it is 90 0 V and across the inductor it is 50 0 V What is the rms voltage of the source VR V V sin 2 ft 14 31

A 100 2 resistance and a capacitor of 100 92 reactance are connected in series across a 220 V source When the capacitor is 50 charged the peak value of the displacement current is a 2 2 A c 4 4 A b 11 A d 11 2 A NEET II 301

10 An inductor L 0 03 H and a resistor R 0 15 k2 are connected in series to a battery of 15V EMF in a circuit showr below The key K has been kept closed for a long time Ther at t 0 K is opened and key K is closed simultaneously A t 1 ms the current in the circuit will be e5 150 6 7 mA 0 03 H vooo 15V K 0 15 k K b 0 67 mA

In a series resonant LCR circuit the voltage across R is 100 volts and R 1 k2 with C 2uF The resonant frequency w is 200 rad s At resonance the voltage across Lis a 2 5 10 2 V b 40 V c 250V d 4 10 V

Question 23 X In the circuit shown in figure Xc R 2 9 i the value of x M M 4 00 through source is R wwwwww C HH ooooo N M 0 00 the peak value current xVo 2R Find

Question 18 M M 4 00 Three alternating voltage sources V 3 sin oot V 5sin ot volt and connected Q 3 volt N M 1 00 V 5sin ot across a resistance R as shown in the figure corresponds where and to 30 and 127 respectively Find the peak current in Amp through the resistor 7 352 volt

5 An L C 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 the circuit is closed be t 0 At what time is the energy stored completely magnetic a t 0 c t 3 14 ms b t 1 57 ms d t 6 28 ms