AC Circuits Questions and Answers

hoke coil and pure resistance are connected in series across 230V 50HZ AC supply If the voltage drop across the coil is 190V and a resistance is 80V while the current drawn by the circuit is 5A Calculate 1 Internal resistance of the coil R1 2 Inductance of the coil XL 3 Resistance value of R2 4 Power factor of the circuit 5 Power consumed by the circuit Coil I SA XL R 190vVR 80V Y 50 HZ

An ideal DC source of emf E is connected with an uncharged capacitor and inductor If switch is closed at t 0 what is the maximum charge on the capacitor in subsequent flow of charge L C Question Type Single Correct Type 1 2 2CE E CE

The output voltage taken across the resistance of a L C R series resonant circuit falls to half its peak value at a frequency of 200 Hz and again reaches the same value at 800 Hz The bandwidth of this circuit is d 600 Hz b 200 3 Hz c 400 Hz a 200 Hz

CO1 1 TCON 2 SBUF 3 TMOD 4 PSW 5 PCON i contains status information ii timer counter control register iii idle bit power down bit iv serial data buffer for Tx and Rx v timer counter modes of operation O 1 v 2 iii 3 ii 4 iv 5 i O 1 iii 2 ii 3 i 4 v 5 iv O 1 ii 2 iv 3 v 4 i 5 iii O 1 i 2 v 3 iv 4 iii 5 ii

23 Show that voltage and current are in phase with each other when an AC voltage is applied across a resistor Represent this relation in phasor diagram 24 Derive the law of reflection of light on the basis of

3 The phase shift in the electric and magnetic fields in an EM wave is given by which parameter a phase constant b attenuation constant c propagation constant intuingia impodance

14 An inductor and a resistor are connected in series across A C supply Which of the following phasor NCERT Pg 239 diagram may be correct 1 3 2 1 3 TU 2 2 4 TU 3 TC 3

For the network shown below R 2 Q R 4 5 Q R 40 XL 30 Xc 3 5 Q R E 100 V 20 z F R a Calculate the total impedance ZT b Compute I c Calculate 1 and 1 d Find the average power delivered to the circuit voo R3 w

A capacitor of capacitance 1 F is charged to a potential of 1 V It is inductance 10 3 H The maximum current that will flow in the circuit has the value 1000 mA 2 1 mA z

In a series LCR circuit L 10 H C 160 uF and R 80 Q The value of angular frequencies for which the power is half of its maximum value are nearly 46 rad s and 50 rad s O 21 rad s and 29 rad s 26 rad s and 34 rad s 26 rad s and 30 rad s

An a c generator consists of a coil of 1000 turns and cross sectional area of 3m rotating at a constant angular speed of 60 rad s1 in a uniform magnetic field 0 04 T The resistance of the coil is 5000 Calculate the maximum current drawn from the generator a b C d 2500 A 1 44 A 6 25 A 0 55 A

Graph shows voltage V and current 1 against time for an AC circuit where all elements will be in series Circuit may contain V I uestion Type Single Correct Type 1 2 3 A L C only L only L R only R Conly

For the AC circuit shown in figure select the correct alternative s 1 2 X 30 mmm 4 R 40 www wwwwww R 50 V V sin ot 1 and V are in same phase 8 Power factor of circuit is cos where 8 is 2 7 phase difference between voltage V and current 2 Power factor of circuit is zero Power factor decreases on increasing

5 Paragraph for Questions 5 and 6 The circuit consists of a capacitor connected in parallel to a resistor R with a coil of inductance L in series with them The power source could be an AC or a constant voltage DC source When AC source is applied then X Xc R L 000000 A The peak value of current through AC source will be If an AC source E cos cot is applied across the input terminal then 280 R B The peak value of current through AC source will be 0 C The peak current across capacitor will be R 200 D C R 80 2R

An inductance has a high resistance to AC and low to DC When a DC voltage source having some AC component superimposed on it sends current through an inductance to a load resistance a the DC voltage falls appreciably across the load and AC component falls by only a small amount b the AC voltage and DC voltage falls by the same amount c both AC and DC voltage falls by the same small percentage d both AC and DC voltage falls to nearly zero

5 2 The potential difference and the current i flowing through an instrument in an AC circuit of frequency f are given as V cos oot volts and i 2sinot amperes The power dissipated in the instrument is A Zero C 5 W B 10 W D 2 5 W

rough 5 7 The ratio of secondary to the primary turns in a transformer is 5 If the power output be P the input power neglecting all pated losses must be equal to en as A 5P C P 5 B P D None of these

5 An inductor L a capacitor C and ammeters A A2 and A3 are connected to an oscillator in the circuit as shown in the adjoining figure When the frequency of the oscillator is increased then at resonant frequency the ammeter reading is zero in the case of a ammeter A c ammeter A3 H C 0000000 L A1 A A3 Fig 36 3 DCE 2002 b ammeter A d all the three ammeters

Case Study Read the following paragraph and answers the questions Resonant Series LCR Circuit When the frequency of ac supply is such that the inductive reactance and capacitive reactance become equal the impedance of the series LCR circuit is equal to the ohmic resistance in the circuit Such a series LCR circuit is known as resonant series LCR circuit and the frequency of the ac supply is known as resonant frequency Resonance phenomenon is exhibited by a circuit only if both L and C are present in the circuit We cannot have resonance in a RL or RC circuit A series LCR eircuit with 10 12H C480 R 23 2 is connected to a 230 V variable frequency supply 52 Find the value of source frequency for which current amplitude is maximum a 222 32Hz b 550 52Hz c 663 48Hz d 770Hz 53 The value of maximum current is XL XL R ww eeee

Question J If potential difference across a resistor of 80 2 varies as shown in the graph below average power consumed by the resistor is Y a b c d e 400 0 400 Zero 500W 1000W 2000W Y 0 02 t sec X

Consider the following statements w r t LCR circuit Statement A Instantaneous values of voltage across various components of series LCR circuit follows Kirchoff s voltage law Statement B RMS values of voltage across various components of series LCR circuit follows Kirchoff s voltage law Which of the following is correct A only O B only O A B both

W r t voltage for the phase of current in ac circuits match the following a Purely resistive circuit I b Purely inductive circuit ii o c Purely capacitive circuit iii 2 Nja min 2

For a purely inductive circuit having inductor of inductance 50 mH and an ac source of 220 V if frequency of source is 50 Hz the rms current is nearly 28 A O 14 A 15 A

In a series LCR circuit L 2 H R 10 Q C 32 F If the voltage of ac source in given by V 300 sin 100nt then at t 1 600 second when instantaneous charge q on capacitor and current 1 are 640 C and 2 A respectively the rate of change of current across inductor is 45 A s 55 A s

current through the circuit immediately after closing the switch Column l Column II A B C R S 2 R Q R 2R 9 Q R p P Q R Vo 4R Vo R Vo 2R

In a series LCR circuit the variation of peak current im with angular frequency w is shown for two cases with different resistances R and R R Then is ac source is same i A 1 4 714 000 R R

The phasor diagram shown below represents cot Purely inductive circuit Purely resistive circuit Purely capacitive circuit LCR circuit

In order to have a better selectivity for a device operating on LCR circuit it is possible that O Inductance is high Band width is low Resistance is low min sec O All of these

In a series LCR circuit the resonance frequency wo is 1 x 106 rad s the resistance R is 2000 and the inductance is 1 mH then the value of quality factor is 4 O 5 O 6

The LC oscillations appears to be unrealistic and undergo damping effect due to Resistance of inductor min sec Energy radiation as as electromagnetic waves Both 1 2

Consider the circuit shown below having a capacitor of capacitance C and a resistance R connected to a source of voltage Vand angular frequency w then current in circuit Xc capacitive reactance R www V 0 OV IR IXC O V IR IX V IR IX

In a series LC circuit performing LC oscillation the quantities that oscillate are Energy of inductor Polarity of capacitor Capacitance min se Both 1 8 2

A charged capacitor having charge Q and capacitance Cis connected to inductor of inductance L as shown If the charge at any instant on capacitor is reduced to half of its initial value then the current in the circuit is neglect resistance of inductor and any radiation Q C 3Q 4LC S ele L

3 Derive the average value and RMS value of a cosinusoidal signal Also find its peak factor and form factor 4 I have a RLC load connected in series with an alternating voltage source Will the circuit behave as resistive or inductive or capacitive Explain with proper phasor diagrams 5 How is charging a battery different from discharging Do all batteries support charging and discharging

Consider an electric circuit consisting of a coil of negligibly small inductance consisting of N 10 turns and with the surfac area of a single loop S 10 cm resistors R R 3 capacitor C 0 2 F and an inductance L 1 H connected as shown in Figure At the moment of time t 0 a magnetic field parallel to the axis of the coil is switched on The induction the magnetic field starts growing linearly starting from B 0 until the maximal value B 1 T is achieved at t 10 ms Furt the induction of the magnetic field remains constant and equal to 1 T C QH B Find the current through the resistors R at the moment of time t 5 ms O 5 mA 10 mA O 20 mA R 40 mA

4 Points Consider a circuit in which a coil having inductance of 0 02H and resistance of 50 connected across 200V 50Hz supply in series with a resistance of 50 Considering all parameters with their behavior determine following below 1 Evaluate capacitive reactance of the circuit 2 Calculate inductive reactance of the circuit 3 Determine power factor of the circuit I

Q 1 In a campus a building is carrying three phase 440V 50Hz ac supply and carrying some electrical equipments for working on a machine In a room there is a 4 pole induction motor and its slip is to found be 0 04 Calculate given below parameters by considering all values a Speed of revolving field relative to the stator structure b Frequency of rotor current

Q 11 In an industry an engineer is designing a dc shunt machine which behaves as a motor He is connected an armature resistance of 0 030 and shunt resistance of 21002 in dc shunt motor When he gives supply of 210V dc then motor runs at a speed of 1200rpm Initially dc shunt motor works at no load and motor is taking 3A current Now when he places a load so motor takes 41A current Then evaluate a Armature current in dc shunt motor b Back emf in dc shunt motor

0 5 points Save Answ The capacitor in the circuit shown is initially charged to Q Qo At t Othe switch is connected to position a At t to the switch is immediately flipped from position a to position b Which of the following graphs best represents the time dependence of the charge on C Charge R to b C time www 3R Charge to time O 9 Charge to time Charge ta time Charge ta time

Draw the diagram for self inductance and mutual inductance and express how can we get coefficient of coupling

ASSAGE A student is performing on 220 v dc shunt motor in which he uses an armature resistance of 0 22 ohm and field resistance of 110 ohm At no load motor takes input current of 15 A and at full load it takes 20 A if the motor runs at a speed of 1200 rpm at no load then examine following Evaulate the back emf of dc moto OPTIONS 220 6 V

A student is working on 3 phase 50 Hz 4 pole induction motor having slip 5 Then selecting the value of slip determine following Calculate the rotor frequency at standstill condition OPTIONS 45 Hz 50 Hz 55 Hz

PASSAGE In de shunt motor if the supply voltage is 400 volt armature resistance is 0 5 ohm and armature current at no load is 5A and at full load 50 A The speed of dc motor at full load is 1200 rpm Then examine following Choose the correct option Marks 2 Calculate the speed of dc motor at no load if full load speed becomes 1500 rpm OPTIONS 1500 rpm 1575 rpm 1590 rpm

5 In an AC circuit the emf e and the current I at any instant are given respectively by e Eo sin ct I Io sin t o The average power in the circuit over one NEED TO cycle of AC is a me b c Eolo 2 Eolo cos o Eolo 2 d Eolo sin olo

Initially there is no current in the inductors and capacitor is charged to a potential difference Vo Then the maximum energy stored in the inductor L after the switch is closed eeeeeee 3L www HE S Options 1 CV 2 2 CV3 3 CV 5 33 5 V2 2L 8000000

Q 3 A three phase 440V 50Hz ac supply is given on a machine in which there is a 6 pole and its slip is to found be 0 03 Analyze the performance of induction motor by calculating its unknown parameters a Speed of revolving field relative to the stator structure b Rotor speed relative to the stator structure I

4 I have a RLC load connected in series with an alternating voltage source Will the circuit behave as resistive or inductive or capacitive Explain with proper phasor diagrams urront of 6 5A and absorbs 187 W IF the resistance

In an L C circuit shown in the figure C 1F L 4H At time t 0 charge in the capacitor is 4C and it is decreasing at a rate of 5 5 C s The maximum charge in the capacitor is nC then value of n will be 66060

Q 13 In any plant an engineer is designing a dc shunt motor in which an armature resistance of 0 060 and shunt resistance of 1150 have been connected When he gives supply of 230V dc then motor runs at a speed of 1500rpm Initially dc shunt motor works at no load and motor is taking 5A current Now when he adds any load then motor takes 21A current Then calculate a Back emf of dc shunt motor at no load b Back emf of dc shunt motor at full load c Ratio of speed at no load to full load

For the circult shown below E 30 V L 36 mH and R350 After steady state is reached with S closed and S open S is closed and immediately thereafter at t 0 5 R www S 0000 a Determine the current through L in A at t 0 8 57 b Determine the current through L in A atf 4 0 x 10 c Determine the voltages across and in V atr 4 0 104