AC Circuits Questions and Answers

4 In he value of resistance R if the total voltage is in phase with the total current is nearly 2022 www 1 24 22 2 892 3 12 92 4 10 Q R Xc 40 Q 41 mooooo X 48 22 FA Xe xxx R B 1 C

Alternating Current 127 20 If reading of voltmeter V shown in the figure at resonance is 200 V then the quality factor of the circuit is 1 2 2 4 3 1 4 3 wwwmmmmm 50 V

In the circuit shown currento comes out to be is 10 R 110 L m NV 2R X X cosmt value of N

An alternating voltage V 200 2 sin 100t where Vis in volt and t in seconds is connected to a series combination of 1 F capacitor and 10k2 resistance through an ac ammeter The reading of the ammeter mA The value of n is

a 3000 resistance If a 20V 200 Hz ac source is connected across the combination the phase difference between the voltage and the current is 2 tan 1 tan 3 tan 5 4 3 A 4 tan 4 5 4

An LCR series circuit contains L 8H C 0 5 F and R 1000 The resonant frequency of he circuit is 1000 1 3 70 Hz 250 7L Hz 2 500 Hz 125 TL Hz

A direct current of 5 amp is superimposed on an alternating current I 10 sin at through a wire The effective value of the resulting current will be 5 x The value of x is

In a circuit resistance R capacitance C and inductance L are in series with a sinusoidal power source If the voltages across R C and L are 80V 10V and 70V respectively then the voltage across the source terminals will be 1 100 V 3 140 V 2 110 V 4 160 V

ce L a capacitance C and resistance R may be connected to an AC source of angular frequency w in three different combinations of RC RL and RLC in series Assume that The power drawn by the three are P P2 P3 respectively Then 2 P P P L 1 C combinations 1 P P P3

Resonant frequency of a series LCR circuit is 600 Hz Quality factor of the circuit is 4 Banc width is 1 300 Hz 3 1200 Hz 2 150 Hz 4 450 Hz

A series R L circuit is subjected to an alternating voltage given as v vosinot Then the variation of peak current 1 with frequency v is denoted by CIVIL dzio sir izio L 1 3 tr 2 Av 4 V

Illustration 4 A series circuit consists of a resistance of 1502 an inductance of 0 08 H and a condenser of capacity 30 F The applied voltage has a frequency of 500 radian sec 1 By what angle will the current lead to or lag behind the applied voltage

turn ratio is 50 If primary coil is 1 k then secondary coil will be In transformar resistance resistance 1 50 k OF X 3 25 MO 2 25 kn EA 4 25 MO

The instantaneous values of alternating current and voltage in a circuit are given as 1 T sin 100nt A and E 2 The average power in watts 1 n The value of n 1 sin 100xt n 3 V 2 consumed in the circuit is

From an L C R series circuit the quality factor is 4 If C 8 F and R 202 then the value of the inductance is 1 8 uH 2 512 uH

A 220 V main supply is connected to a resistance of 100k2 The rms current is 1 2 2 mA 2 2 2 mA 3 2 2 2 mA 4 None of these

A capacitor of 1 F is charged and then connected across an ideal inductor of 10 mH The angula frequency of oscillation of the charge in rad s is 1 10 8 2 108 3 104 4 10 4

An L C R series circuit with 100 2 resistance is connected to an AC source of 200 V and angular frequency 300 rad s When only the capacitance is removed the current lags behind the voltage by 60 When only the inductance is removed the current leads the voltage by 60 The current in A is n The value of n is

In L C oscillator initially current is maximum then instant when capacitor has maximum energy first time 1 LC 2 LC

When an ac source of emf E Eo sin 100t is connected across a circuit the phase difference between the emf E and the current I in the circuit is observed to be 4 as shown in Fig If the circuit consists possibly only of R C or R L or L C in series the relationship between the two elements 1 I ps 1 R 1kQ C 10 F 3 R 1k01 10H 2 R 1k02 C 1 F

An ac voltage is applied to a resistance R and an inductor L in series If R and the inductive reactance are both equal to 302 the phase difference between the applied voltage and the current in the circuit is 1 zero 3 4 2 E 6 FIN 4 7 2

35 Which of the shown graphs may represent the reactance of a series L C combination Reactance Reactance a c Reactance Frequency Frequency b Reactance d Frequency Frequency

100 Hz AC current of crest value 1 A flows TC through the primary of an ideal transformer If the mutual inductance between the primary and secondary be 0 5 H the crest voltage induced in the secondary is 1 75 V 3 100 V A 24 2 150 V 4 None of these

26 In an oscillating L C circuit the maximum charge on the capacitor is Q The charge on the capacitor when the energy is stored equally between the electric and magnetic field is 1 3 0 N 2 2

20 If reading of voltmeter V shown in the figure at resonance is 200 V then the quality factor of the circuit is 1 2 2 4 3 1 mmmmm 50 V

An alternating emf is applied across a parallel of a resistance R capacitance C and a L If IR IL and Ic are the currents through R L and C respectively then the diagram which correctly represents the phase relationship among IR IL Ic and source emf E is given by IR IL combination inductance a c Ic Ic IR E b E d Ict IRT IL E E

19R The frequency of an alternating current is 50Hz The minimum time taken by it in reaching from zero to peak value is 1 5ms 4 50ms 2 10 ms 3 20 ms

A capacitor C 2 F and an inductor with L 10 H and coil of resistance 50 are in series in a circuit When an alternating current of rms value 2A flows in the circuit the average power in watts is 1 100 2 50 3 20 4 10 in the same direction If the loops

A voltage waveform is as shown V 0 V R M S value of voltage is 1 Vo Vo 2 2 1

wave rectifier is 40 6 and of full wave rectifier is 81 296 r 1 21 for FWR asurement is given by a factor called ripple factor For good rectifier ripple factor must be very low factor r In the output of rectifier some A C components are present these are called nipples Dark current When no light is incident then the reverse saturation current in photo diode is called dark current r 0 48 LED have less power and low operating voltage Solar cell converts solar energy into electrical energy Zener diode is heavily doped with thin depletion region for HWR istration 11 2 If in a p n junction diode a square input signal of 10 V is applied as shown Then the output signal across R be AIEEE 20 5 V n 2 10 V 5 V 5 V 3 T R 10 V 4 5 VL

The diagram shows a capacitor C and a resistor R connected in series to an AC source V and V are voltmeters and A is an ammeter Consider now the following statements 2 1 I only and II only A R I Readings in A and V are always in phase II Reading in V is ahead with reading in V III Readings in A and V are always in phase Which of these statements are is correct 2 II only 4 II and III only www

9 In the circuit shown in figure the current measured by ammeter Is 60 V 100 V V 1 3 1A 3 A wwwww vo v vo vo v R 102 A 50 V V 2 2 A 4 Zoro

A capacitor and a bulb are connected in series with a source of alternating emf If a dielectric slab is inserted between the plates of the capacitor then 1 The brightness of the bulb decreases 2 The brightness of the bulb increases 3 The brightness of the bulb remains same TI

Equation of alternating current is given by 10 2 sin 100rt TU 6 root mean square value from t 0 is t then the value of t is 1 3 1 1200 1 S 200 S 2 4 1 250 1 800 S S The time taken by current to reach the

In the circuit shown a 30 V d c source gives a current 2 0 A and a 30 V a c source of frequency 100 Hz gives a current 1 2 A The inductive reactance is 1 10 S 7 g s 20 20 Q

29 The maximum efficiency of a full wave rectifier is 8 4 80 1 4 T 3 40 100 2 100 27 R

51 In the circuit below A and B represent two inputs and C represents the output The circuit NOT represents 1 NOR gate 2 AND gate 3 NAND gate A Ro Z

In a circuit L C and R are connected in series with an alternating voltage source of frequency f The current leads the voltage by 45 The value of C is AIPMT Prelims 2005 1 1 2nf 2nfL R 31 1 1 2 f 2 fL R 1

The impedance of R C circuit is Z for a frequency f and Z for frequency 2f Then Z is 1 Between 1 and 2 2 2 1 3 Between and 1 4 4 1 2

In the circuit shown in figure the potential difference across 10 F capacitor is B 9X Zero 3 36 V A 49 3 F www 2Q 10 F 54V 6 F 2 18 V 4 54 V

27 The equivalent inductance of two inductor is 2 4 H when connected in parallel and 10 H when connecte series The difference between two inductance is Neglecting mutual induction between coils 1 2 H 2 3 H 3 4 H 4 5 H

factor c the bandwidth d the cutoff frequencies e the magnitude of current I and the series resonant circuit shown below find a The resonant frequency b the quality magnitudes of the voltages VR VL and Vc at resonance I E 25 Volts 40 C 0 05 F H Vc Mg VR L 80 mH R 60 S2

A 130 V 200Hz power supply is connected across a 10 k resistor 0 05 capacitor and a 10 H coil in series Find X Xc Z 8 I and P

1 A 12 0 V storage battery is connected to three resistors 5 0 Q2 10 0 02 and 15 0 2 respectively The resistors are joined in series a Calculate the total resistance b What is the current in the circuit 2 A 4 0 2 resistor 8 02 resistor and a 12 0 2 resistor are connected in series with a 24 0 V battery a Calculate the total resistance b Calculate the current in the circuit c What is the current in each resistor

A 1200 V power source is applied to a step down transformer with 4200 turns in the primary coil and 840 turns in the secondary coil What is the secondary voltage 6000 V 2 8 V O 240 V O 1200 V

AC Source V Electrical Path Fig Purely Capacitive Circuit An 9 80 F capacitor is connected to the terminals of an AC generator with an rms voltage of 1 70 x10 V and a frequency of 70 0 Hz Find the capacitive reactance Xc and the rms current Imms in the circuit 232 0 733 A O 232 0 332 A Purely C Capacitive Load O 733 0 230 A O 17 35 0 237 A

on 19 A coil with an inductance 0 14 H and a resistance of 12 ohm is connected acros V 25 Hz source What would be the phase angle between the current and supp voltage 61 3 106 50 0 13 5

A series LRC circuit consists of a 10 00 pF capacitor a 7 5 mH inductor a 75 0 Q resistor and a 50 0 V ac power source of variable frequency At what frequency will the impedance of this circuit be equal to 75 0 1

If the voltage amplitude across an 8 50 nF capacitor is equal to 12 0 V when the current amplitude through it is 3 33 mA the frequency is closest to O 32 6 Hz O 32 6 MHz O 5 20 kHz O 32 6 kHz O 5 20 MHz

Question 37 A coil has an inductance of 1 5 H and a resistance of 0 6 ohm If the coil is suddenly connected across a 12 V battery find the time required for the current to rise to 0 63 of its final value 2 9 s 5 8 s O 5 2 ms 1 pts 2 5 s