Question bank for Basic Electrical and Electronics Engineering

Basic Electrical and Electronics Engineering

Question Bank

UNIT 1

Part A.

1.      Define Ohm’s Law.

2.      Define Kirchhoff’s Laws.

3.      Define Series Parallel connection.

4.      What is meant by open circuit and short circuit?

5.      Define the dependent source of a circuit.

6.      Define the independent source of a circuit.

7.      List the active and passive elements of electric circuit.

8.      What is node?

9.      Define the branch of a circuit.

10.  What is the difference between and Network?

11.  Define active and passive elements.

12.  A 10A current source has a source resistance of 100ohm, what will be the equivalent voltage source?

13.  Two resistors R1= 10ohm and R2 = 15ohm connected in parallel in a circuit, Find out the total resistance of the circuit?

14.  What s single loop circuit?

15.  A 2KW, 220W water heater is used to heat a water tank for 45minutes. What will be the number of units of energy consumed?

16.  Mention the limitations of Ohm’s Law.

17.  Explain how voltage source with a source resistance can be converted into an equivalent current source.

18.  Name the four different types of dependent sources in electric circuits.

19.  Define an ideal voltage source.

20.   Define an ideal current source

Part B.

           

1. State Superposition theorem.
2. State Thevenin’s theorem.
3. State Norton’s theorem
4. State Maximum power transfer theorem.
5. Find the current through 3 ohm resistor using superposition principle of figure.

           

6.      Find the current through 10 ohm resistor using mesh analysis.

7.      Given that the resistors Ra, Rb and Rc are connected electrically in star. Write the

equations for resistors in equivalent delta.

8.      Three resistors Rab, Rbc and Rca are connected in delta. Write the expression for

resistors in equivalent star.

9.      Explain with relevant diagrams:

i) Kirchoff laws.

10.  Explain with relevant diagrams: (i) Dependent sources (i) Independent sources

11.  Explain with relevant diagrams: Voltage division and current division rule

12.  Find the node voltages of the following circuit.

Part C.

1.      Find the current through each branch by network reduction technique.

2.      Calculate a) the equivalent resistances across the terminals of the supply, b) total current supplied by the source and c) power delivered to 16 ohm resistor in the circuit shown in figure.

3. In the circuit shown, determine the current through the 2 ohm resistor and the total

Current delivered by the battery. .

4.      Find the current through each element using mesh analysis

5.      Using mesh analysis, find the current through 4 ohm resistor.

6.      Use the nodal analysis to find the node voltages V1, V2 and V3.

7.      Find the node voltages of the circuit shown below.

8.      For the circuit shown, use superposition theorem to compute current I.

9. Find the Thevenins’s equivalent circuit of the circuit shown below, to left of the

terminals ab. Then find the current through R_L = 16 ohm.

10. Find the value of RL so that maximum power is delivered to the load

            resistance shown in figure.

11. a) State and explain maximum power transfer theorem for variable Pure resistive

          Load.

      (b) Using Norton’s theorem, find current through 6 ohm resistance shown in figure.

UNIT II

Single Phase AC Circuits

Part A.

1.      Define frequency of AC voltage.

2.      Define time period.

3.      Define Average value.

4.      Define R.M.S value.

5.      Define form factor.

6.      Define Peak factor.

7.      A load consisting of 3 ohm resistance 4 ohm inductive reactance draws a current of 10A when connected to a sinusoidal source. Determine Voltage in the circuit.

8.      A sinusoidal current is given by the equation, i(t) = 7.072 sin314t A. What is the RMS and average value of the current?

9.      An inductive load consumes 1000W power and draws 10A current when connected to a 250V, 25Hz, supply, Determine the resistance of the load.

10.  A RC series circuit with R= 1.2 Kilo ohm and C = 0.1 micro farad is excited by a sinusoidal source of 45V and frequency 1KHz. Find the impedance.

11.  A voltage source has internal impedance (4+j5) ohm. Find the load impedance for maximum power transfer.

12.  what is power factor?

Part B

1.      Determine the Thevenin’s equivalent for the figure

2.      Derive expressions for star connected arms in terms of delta connected arms

3.      Derive expressions for delta connected arms in terms of star connected arms.

4.      Determine the Thevenin’s equivalent circuit.

5.      State and prove Norton’s theorem.

6.      State and prove Maximum power transfer theorem.

7.      For the circuit shown, determine the current in (2+j3) ohm by using superposition theorem.

8.      Find the current through branch a-b network using Thevenin’s theorem.

Part C

1.      Using superposition theorem calculate current through (2+j3) ohm impedance branch of the circuit shown.

2.      A circuit is composed of a resistance 6 Ω and a series capacitive reactance of 8 Ω. A voltage e(t)=141 sin 314t is supplied to the circuit. Find (i) Complex impedance, (ii) Effective value of current, (iii) Power delivered to the circuit, (iv) Capacitance of the capacitor.

3.      A series RLC circuit is connected to a 230V, 50hz, 1-phase AC supply. The value of R=5Ω, L=13mH and C=140μF. Find total reactance, impedance, current drawn by the circuit and p.f of the circuit.

4.      A resistance of 20 Ω and an inductance of 0.2H and a capacitance of 100 μF are connected in series across 220V,50 Hz main. Determine (i) Impedance (ii) current taken from mains, (iii) Power and power factor of the circuit.

5.      A coil of resistance 10 Ω and inductance 0.1 H is connected in series with a 150 μF capacitor across 200V,50 Hz supply. Calculate (i) Inductive reactance, Capacitance reactance, impedance, current and power factor. (ii) The voltage across the coil and capacitor respectively.

6.      A series circuit having pure resistance of 40 Ω, pure inductance of 50mH and a capacitor is connected across a 400V, 50 Hz ac supply. This LC circuit draws a current of 10A. Calculate 1) Power factor of the circuit, 2) Capacitor value.

7.      A series RLC circuit has R=33Ω, L=50mH, and C=10μF. The supply voltage is 75 V with a frequency of 200Hz. Calculate supply current, voltage across each component, and Real, Reactive and Complex power. Draw the phase diagram.

8.       A parallel circuit has three branches having resistor R=33Ω in first branch, Inductor L=50mH in second branch, and Capacitor C=10μF in third branch. The supply voltage is 75 V with a frequency of 200Hz. Calculate total current and Current in each Branch and also draw the phase diagram.

9.      Find the value of impedance Z so that maximum power will be transferred from source to load for the circuit shown.

10.  Solve for V1 and V2 using nodal method. Let V = 100V.

UNIT III

Three Phase Circuits

1.      What is balanced voltage?

2.      What are balanced impedance?

3.      What is phase sequence?

4.      Write the relation between the line and phase value of voltage and current in a

balanced star connected load.

5.      Write the relation between the line and phase voltage of voltage current in a balanced

delta connected load.

6.      What is neutral shift voltage?

7.      Write the relation between the power factor and wattmeter readings in two-wattmeter

method of power measurement.

8.      In three phase circuit, what do you mean by balanced load?

9.      When is a three phase supply system called balanced supply system?

10.  List any two advantages of 3-phase system over 1-phase system.

11.  Define line voltage

12.  Define phase voltage

13.  Define line current

14.  Define phase current

Part B

1.      Derive the power relationship for three phase power

2.      Derive the star connection with phasor diagram

3.       Derive the delta connection with phasor diagram

4.      Draw the phasor diagram for star connection

5.      Draw the phasor diagram for delta connection

6. what is apparant power and reactive power?

7. compare between star and delta connection

8. write the expression for line voltage of three phase star connection

9. write the expression for line current of three phase star connection

10. write the expression for phase voltage of three phase star connection

11. write the expression for phase current of three phase star connection

12. write the expression for line voltage of three phase delta connection

13. write the expression for line current of three phase delta connection

14. write the expression for phase voltage of three phase delta connection

15. write the expression for phase current of three phase delta connection

16. A balanced star connected load of 3 + 4jΩ is connected to 500v,60hz three phase supply. Determine the total active power produced by the system.

17. A star connected system has a balanced load of 6 - 8jΩ connected to a 440v. determine power factor, total active power

18. A balanced three phase 500v system supplies a balanced delta connected load of 12Ω resistance and 15 Ω inductive reactiance. Determine the line current, power factor and total power.

19.a balanced delta connected load three phase load draws 25 kW power, a leading power factor of 0.707 when it is connected to a supply of 240v, 50hz. Determine the load parameters.

20. In a delta connected system if I_R = 12∟300 and IB = 40∟600 .determine the line current I_Y.

Part C

1.      For the circuit given below calculate the following by considering the line voltage 440V and the frequency is 60Hz.

i) Phase voltage of all the three phases both magnitude and directions.

ii) Line current and phase current of all the three phases both magnitude and direction

iii) 3 Phase real power

iv) 3 phase Reactive power

v) 3 Phase Complex power

vi) Scaled phasor (Argand) diagram

2.      Repeat the Q1 with DELTA connection and calculate the following

i)Line current and phase current of all three phases with magnitude and direction.

ii) 3 Phase real power

iii) 3 phase Reactive power

iv) 3 Phase Complex power 

v) Scaled phasor (Argand) diagram indicating

3. For the circuit shown below is being feed by 440v, 50 Hz power supply and the load is a balanced one comprising of (36 + j 48) Ω on each phase. Calculate the following.

i) Line current and phase current of all the three phases both magnitude and directions.

ii) 3 Phase real power

iii) 3 phase Reactive power

iv) 3 Phase Complex power

v) Scaled phasor (Argand) diagram indicating

4. The circuit is being feed by 440v, 50 Hz power supply and the load is a balanced one comprising of (36 + j 48) Ω on each phase connected in star connection. Calculate the following.

i) Phase voltage of all the three phases both magnitude and directions.

ii) Line current and phase current of all the three phases both magnitude and direction

iii) 3 Phase real power

iv) 3 phase Reactive power

v) 3 Phase Complex power

vi) Scaled phasor (Argand) diagram indicating

5.The star-connected load consists of a resistance of 15 Ώ, in series with a coil having resistance of 5 Ώ, and inductance of 0.2 H, per phase. It is connected in parallel with the delta-connected load having capacitance of 90 μF per phase . Both the loads being balanced, and fed from a three-phase, 400 V, 50 Hz, balanced supply, with the phase sequence as R-Y-B. Find the line current, power factor, total power & reactive VA, and also total volt-amperes (VA).

6. A balance load of (16+j12)Ω per phase, connected in star, is fed from a threephase, 230V supply. Find the line current, power factor, total power, reactive VA and total VA.

7. a star connected system has balanced load of 5 + j8Ω connected to a three phase supply of 220v, 50hz. Determine phase voltage, line current, power factor, total power, reactive power, apparent power and draw the phasor diagram.

8.in a balanced star connected system the total power consumed is 10KW when the input volt ampere is 18KVA.if the line current is 12 A, determine the circuit elements, total VAR when the supply frequency is 60Hz.

9. in a delta connected system total power consumed is 12KW when the input  volt ampere is 20KNA. If the line current is 10A, find the load resistance and inductive reactance, power factor and total VAR when the supply frequency is 50 Hz.

10. in a unbalanced star connected load 10Ω in R phase, 20 Ω in B phase, 15 Ω in Y phase are connected to 230v, 3 phase supply. Determine the line current .

11. A star connected load with isolated neutral has impedance at each of its phase ZR = 12∟45o , ZY = 8∟30o , ZB = 5∟90o. If the supply voltage is 240V find the line current, plase current, line voltage, phase voltage, power factor.

12. Three RESISTIVE loads each of 30 ohms are connected in STAR to a 415 volt 3 phase supply.

Draw the circuit diagram. Label on the diagram Vph, VL, IL and Iph and determine

the following:

(a) (i) Phase voltage (ii) phase current (ii) Line current

(b) Draw the phasor diagram showing relationship between phase currents and phase voltages

13. A star connected load consists of 3 identical coils each of resistance 30 ohms and inductance  127.3mH. Draw the circuit diagram. If the Line current is 5.08 amps, Calculate the  Line voltage if the supply frequency is 50 Hz. (Remember XL = 2πfL). Calculate the PF  and phase angle and sketch the phasor diagram showing relationship between phase currents and phase voltages

14. The 3 coils in (2) are now connected in DELTA to a 440 volt, 50 Hz 3 phase supply. Draw the circuit diagram. Determine the phase current and the Line current

15. 3 identical capacitors are connected in DELTA to a 415 volt 50 Hz 3 phase supply.  If the line current is 15 amps. Determine the capacitance of each capacitor

(remember XC = 1/ 2πfC

16. 3 coils each of resistance 30 ohms and inductive reactance 40 ohms are connected in  (a) STAR (b) DELTA to a 415 volt 3 phase supply. Calculate for each connection the:-(c) Line and phase voltages (d) Line and phase currents

17. 3 – 12 ohm resistors are connected in STAR to a 440 volt 3 phase supply. Determine the total power dissipated in the resistors

18. The input power to a 3 phase AC motor is measured as 6 kW. If the voltage and current to the motor are 440 volt and 8.6 amps respectively. Determine the power factor of the system

19. Three identical coils each of resistance 20 ohms and inductance 84 mH are connected in  (a) STAR and (b) DELTA to a 440 volt 50 Hz 3 phase supply. Determine the total power dissipated in each case

20. A 3 phase induction motor is supplied from a 415 volt supply operating at full load at  0.8 power factor. The line current is measured at 14 amps.

(a) Calculate the input power to the motor

(b) If the motor is rated at 7 kW, calculate the efficiency of the motor

UNIT IV

PART A

1. what are the types of magnetic material

2. what is dia magnetic material

3. what is para magnetic material

4. what is ferro magnetic material

5. what is permeability

6. definefleming’s right hand rule

7. definefleming’s left hand rule

8. definelenz law

9. what is permanent magnet

10. what is magnetic field

11. define magnetic flux

12. define magnetic flux density

13. define MMF

14. what is magnetic reluctance

15. state faraday’s Ist law

16. state faraday’s IInd law

17. what is self induction

18. what is mutual inductance.

19. what is eddy current loss

20. what is hysteresis loss?

PART B

1. explain in detail about linear magnetic circuits.

2. explain in detail about non- linear magnetic circuits

3. what are the types of magnetic material? Explain

4. explain in detail about faraday’s law

5. Explain in detail about fleming’s rule

6. what are the uses of self induction

7. what is self inductance? Explain

8. what is mutual inductance ? explain

9. what is dynamically induced EMF

10. what is statically induced EMF

11. how the energy is stored in magnetic field?

12. derive the expression for energy stored inductance

13. derive the expression for energy stored capacitance

14. explain in detail about eddy current

15. explain in detail about hysteresis losses

PART – C

1. what are the losses in magnetic field how it is minimized?

2. explain in detail about types of magnetic circuits

3. what is magnetic repulsion ? explain

4. compare electrical circuits with magnetic circuits

5. Explain solenoid with neat sketch

6. explain magnetic hysteresis

7. explain the types of magnetic induction with neat diagram

8. derive expression for series magnetic circuits

9. derive expression for  parallel magnetic circuits

10. Make a sketch of a conductor with a current flowing through it, show the magnetic field and  Its direction

11. What is Magnetising force what is it’s symbol what is it equal to in terms of current, number  of turns and length. Draw typical B/H curves for a nonmagnetic material and one ferromagnetic material

12. A magnetic pole face has rectangular section having dimensions 20cm by10cm. If the total flux  Emerging from the pole is 300 Wb. Calculate the flux density.

13. A flux density of 1.4 T is produced in a piece of cast steel by a magnetising force of 1250 At/m  Determine the relative permeability of the steel.

14. A magnetising force of 8000 At/m is applied to a circular magnetic circuit of mean  diameter of 30 cm by passing a current through a coil wound on the circuit,. If the coil is uniformly wound around the circuit and has 750 turns. Determine the current in the coil.

15. A coil of 300 turns is wound uniformly on a ring of non-magnetic material . The ring has a  mean circumference of 40 cm and a uniform cross section area of 4 cm². If the current in the coil is 5A Calculate (a) the magnetic field strength (b) The flux density (c) The total magnetic flux in the ring

16. (a) A uniform ring of cast iron has a cross section area of 10 cm² and a mean circumference  of 20cm. Determine the mmf necessary to produce a flux of 0.3 mWbs in the ring. Use themagnetisation curve for cast iron (b) If an air gap of 2mm is introduced in the ring and assuming that flux leakage is negligible. Calculate value of magnetic field strength H and mmf for the air gap.

17. The flux linking a coil of 100 turns collapses from 1.8 mWb to zero in 3 ms

Calculate the induced emf.

18. A uniform ring of cast iron has a cross section area of 10 cm² and a  meancircumference of 40cm. Determine the mmf necessary to produce  a flux of 0.6 mWb in the ring. Use the magnetisation curve for cast iron

19. A coil A and coil B are wound on the same iron core. The self inductances are 0.6 H and 0.8 H. If the mutual inductance between the two coils is 18 mHDetermine the co-efficient of coupling

20.A conductor carries a current of 16 A and is at right angles to a magnetic field having a flux density of 0.8 T. If the length of the conductor in the field is 80 cm. Calculate the force acting on the conductor