BASIC ELECTRICAL ENGINEERING [BET-101]

MODULE-I

CH-1 [FUNDAMENTALS]

Q1.The unit of charge is__________

Ans. The unit of charge is “Coulomb”.

Q2.Define current and what is its unit?

Ans. The flow of free electrons in a definite direction in any conductor or semiconductor

material is called electric current. Its unit is “Amper”(Amp. Or A))

Q3.What is the unit of potential difference?

Ans. The unit of potential difference is “Volt”

Q4. What is resistance and what is its unit?

Ans. Resistance is the property of the material, by virtue of which it opposes the flow of

electrons through it. Its unit is Ohm (Ω)

Q5. State Ohm’s law.

Ans. Ohm’s law states that at constant temperature the potential difference between two ends of a conductor is directly proportional to the current flowing between the two ends of that conductor.

Mathematically Vα I

V=RI (R is the constant of proportionality known as resistance)

Q6. Define resistivity.

Ans. Resistivity is defined as the resistance offered by a material of unit length and unit area

of cross section.

R=

==Ωm (Ohm-meter)

Unit is Ω-m or Ω-Cm

Q7. State conductivity.

Ans. Conductivity is the reciprocal of resistivity.

Mathematically conductivity σ = unit is Ω-1m-1

Q8. State Kirchhoff’s current law.

Ans. In any electrical network the algebraic sum of the currents meeting at a point is zero.

∑ I =0

Q9. State Kirchhoff’s voltage law.

Ans. It states that the algebraic sum of all branch voltages around any closed path of

a circuit is always zero.

∑IR + ∑e.m.f. = 0

Q10. State Superposition Theorem.

Ans. This theorem states that in any linear network containing two or more sources, the resultant current in any element is equal to the algebraic sum of the currents caused by individual sources acting alone, while the other sources are non operative

That is while considering the effect of individual sources other ideal voltage sources and ideal current sources in the network are replaced by short circuit and open circuit across their terminals.

Q11. State Thevenin’s theorem.

Ans. This theorem states that any two terminal linear network having number of voltage, current sources and resistances can be replaced by a simple equivalent circuit consisting of a single voltage source in series with a resistance.

Where the value of voltage source is equal to the open circuit voltage across the two terminals of the network and resistance is equal to the equivalent resistance measured between the terminals with all voltage sources are replaced by short circuit and current sources by open circuit.

Q12. State maximum power transfer theorem.

Ans. A resistance load being connected to a DC network receives maximum power when the load resistance is equal to the source resistance (Thevenin’s equivalent resistance) of the source network as seen from the load terminals.

Q13. State faraday’s laws of electromagnetic induction.

Ans. 1st Law: Whenever a conductor cuts the magnetic flux, an e.m.f is induced in that

Conductor.

2nd Law: The magnitude of induced e.m.f is equal to the rate of change of flux

Linkages.

Mathematically, e=-N volt.

Q14. State Fleming’s left hand rule.

Ans. According to Fleming’s left hand rule states that if the thumb, the fore-finger & the middle finger of the left hand are stretched to be perpendicular to each other. If the fore-finger represents the direction of magnetic field, the middle finger represents the direction of current, then the thumb represents the direction motion of conductor. This rule is applicable for motor.

CHAPTER-2

MAGNETIC CIRCUITS

Q1. What is absolute permeability and relative permeability?

Ans. Absolute permeability (µ) of a medium is given by the ratio as follows

µ = =

Relative permeability (µr) of that medium is given by the ratio as follows

µr = =

Q2. What is the value of µ0

Ans. The value of µ0 for free space is 4π X 10-7 H/m.

Q3. What is mmf?

Ans. It drives or tends to drive flux through a magnetic circuit and corresponds to

electromotive force (e.m.f) in an electric circuit. It’s unit is (AT)(Amper-Turn).

Q4. What is the relation between flux density (B), Magnetising force(H) and absolute

permeability(µ)?

Ans. B=µH

Q5. Define Reluctance.

Ans. It is the property of the material which opposes the creation of magnetic flux in it

Reluctance (S)= it’s unit is

Q6. What is permeance?

Ans. It is the reciprocal of reluctance.

Q7. What is the unit of ∅, B, H and S?

Ans. The unit of flux (∅) is weber(wb), Unit of flux density(B) is wb/m2, Unit of Magnetising

force (H) is N/wb or AT/m and unit of Reluctance (S) is

Q8. Give two examples of ferromagnetic materials.

Ans. The examples of ferromagnetic materials are Iron, steel, cobalt, Nickel

Q9.What is magnetic flux? What is it’s unit

Ans. A unit N-pole is supposed to radiate out flux of 1 weber. It ‘symbol is ∅. It’s unit is weber.

CHAPTER-3

A.C THEORY

Q1.State two differences between AC &DC

Ans.

AC

DC

Alternating current is that current

in which magnitude as well as

the direction varies w.r.t time.

Direct current is that current in which the current flows at constant magnitude either ‘+ve” (or) ‘-ve’ w.r.t time.

A.c. has certain frequency.

D.C has no frequency (or) Zero frequency.

Q2. Define Amplitude and frequency

Ans. Amplitude:- The maximum value (Positive or negative) attained by an alternating quantity is called its amplitude or peak value the amplitude of an alternating voltage or curve is denoted by Vn (or Em) or Im.

Frequency:-The number of cycles that occur on one second is called the frequency (f) of the alternating quantity. It is measured in cycles/Sec. (c/sec) or Hertz(Hz) one Hertz is equal to 1c/sec.

Q3. Define Time period.

Ans. Time period:- The time taken in seconds to complete one cycle of an alternating

quantity is called its time period. It is generally represented by T.

Q4. What do you mean by phase angle and power factor?

Ans. Phase Angle:- Phase angle means the angle between the zero position of reference and

the alternating quantity under consideration.

Power factor:- It is defined as the cosine of the angle of lead & lag between the r.m.s

value of supply voltage and the r.m.s value of resultant current.

It is also defined as the ratio of resistance & impendance

Power factor= =

Q5. What is phase difference?

Ans. The difference in phase between two alternating quantities is called phase difference.

Q6. State R.M.S Value.

Ans. The R.M.S value of an alternating current is defined as that DC current which when flowing through a given circuit for a given time produces the same heat as produced by the alternating current when flowing through the same ckt for the same time. It is also said to be the effective (or) virtual value of a.c.

Q7. What is form factor?

Ans. form factor is defined as the ratio

KF= = = 1.11

KF=1.11 (For sinusoidal only)

Q8.What is active Power?

Ans. Active power (P): It is the power which is actually dissipated in the circuit resistance

i.e P=I2R = VI cos∅ Unit is in Watt or KWatt.

Q9. Explain Power Triangle

Ans. Suppose a series R-L circuit draws a current I when an alternating voltage of r.m.s value V is applied to it. So the current lags behind the applied by. Then three powers drawn by the circuit is as follows:

(a)Apparent power(S) :

It is the product of r.m.s value of applied voltage and circuit current

S=VI= (IZ)I=I2Z (Volt Amperes or Kilo Volt Amper)( VA or KVA)

(b)Active power (P ) : It is the power which is actually dissipated in the

circuit resistance i.e P=I2R = VI cos∅ (Watt or KWatt)

(c)Reactive power (Q) : It is the power developed in the inductance

of the circuit Q = I2XL= VI sin∅ (Volt Ampere Reactive) (VAR or KVAR)

10. Determine the impedance if resistance R=3Ω and inductive reactance XL=4Ω

Ans. Impedance Z= = =5Ω

11. Determine the impedance if resistance R = 5Ω and capacitive reactance

XC = 12Ω

Ans. Impedance Z= = =13Ω

Q12.. Form factor value in pure AC 50Hz sinusoidal is__________

Ans. Form factor value in pure AC 50Hz sinusoidal is 1.11

Q13. Draw the waveform / phasor diagram of voltage & current in the purely

resistive circuit.

Ans. Wave form Phasor Diagram

I

VR

Q14. Draw the phasor diagram of voltage & current for a.c Through purely

inductive and capacitive ckt.

Ans. Phasor diagram of voltage & current for AC through purely inductive ckt.

Phasor diagram of voltage & current for AC through purely capacitive ckt.

Q15. Determine the impedance it resistance of 20Ω, an Inductance of 0.2H and a

capacitance of 100µF are connected in series across 220 v, 50 Hz mains ?

Ans. Inductive Reactance XL=2πfL=2xπx50x0.2=62.83Ω

Capacitive Reactance XC= = =31.83Ω

Impedance Z=

=

= 36.89Ω

Q16. Why power factor has no unit?

Ans. Power factor (Cos∅)= , The unit of resistance is Ω and also impedance is Ω , So its ratio has no unit. Hence power factor has no unit.

Q17. What is average value?

Ans. The average value of an alternating current is defined as that steady current which transfers across any circuit the same charge as is transferred by that alternating current during the same time.

CHAPTER-4

GENERATION OF ELECTRIC POWER

Q1. Name one place where you will find a hydroelectric power station in Orissa.

Ans:- Hirakud

Q2. Name any two radioactive elements.

Ans:- The radioactive elements are Uranium (U235), Thorium (Th232) & Plutonium (Pu239) .

Q3. __________ is the main fuel used in Atomic Power plant.

Ans:- Uranium (U235)

Q4. What is the function of moderator in a nuclear plant?

Ans:- The function of moderator is to slow down the neutrons before they bombard the fuel

rods. For moderator Carbon, Heavy water or Ordinary water are used.

Q5. Reactor is used in which power station?

Ans:- Reactor is used in nuclear power station.

CHAPTER-5

CONVERSION OF ELECTRICAL ENERGY

Q1. Write main parts of DC machine.

Ans:- Main parts of DC machine are

i. Field magnets

ii. Armature

iii. Commutator

iv. Brush and Bearings

Q2. What are the functions of a commutator?

Ans:- The function of commutator in DC generator are

i. It facilitate the collection of current from armature conductors

ii. It also converts AC current induced in the armature into DC.

Q3. Sate back e.m.f.

Ans:- When the motor armature rotates an e.m.f is induced in them by the law of electromagnetic induction whose direction is found by Fleming’s right hand rule, is in opposite direction to the applied voltage , because of its opposing direction it is referred as back e.m.f (Eb )

Q4. Why starter is used to start DC motor?

Ans: In dc motors the armature is generally designed to have the least resistance possible. So when starting a dc motor starter is connected such that it limits the current value by being in series with armature and later separates from the circuit. But by then back emf develops in the armature.

Q5. Which motor is used for traction purpose and why?

Ans: DC series motor is used for traction purpose because it has high starting torque which is important in traction system.

Q6. Write down the relationship between line current and phase current in both star and delta connection.

Ans:- Star Connection: Iph=IL

Delta Connection: Iph=IL/√3

Q7. Explain the principle of operation of 3-phase induction motor.

Ans:- It works on the principle that when a current carrying conductor is placed within a magnetic field it experiences a mechanical force.

Q8. Why capacitor is used in fan?

Ans:- Capacitor is used in fan to produce a phase shift . Which enable it to produce a rotating magnetic field and make the motor self starting.

Q9. Write down two uses of shaded pole induction motor.

Ans:- Shaded pole induction motors are used for hair dryers , Record players,

Tape recorders, projectors, photocopying machines

Q10. What is the function of brush in a DC generator?

Ans:- The function of brush is to collect the current from the commutator and supply it to the

external load circuit.

Q11. Write down the principle of operation of a DC generator.

Ans:- The principle of operation of DC generator based upon the principle of dynamically induced e.m.f , according to Faraday’s laws of electromagnetic induction whenever a conductor cuts magnetic flux an e.m.f is induced in the conductor.

Q12. Write down the principle of operation of a dc motor.

Ans:- DC motor works on the principle that when a current carrying conductor placed in a magnetic field it experiences a force whose direction is given by Flemings left hand rule.

Q13. State the basic difference between a DC generator and a DC motor.

Ans:- The basic difference between DC generator and DC motor is that the DC generator converts mechanical energy to electrical energy and DC motor converts electrical energy to mechanical energy.

Q14. What a commutator does in a d.c. motor and in case of a d.c generator?

Ans:- In DC motor commutator converts DC to AC and in DC generator it converts AC to DC

Q15. Write down the different uses of a DC series motor.

Ans:-DC Series motors are used for i) Cranes ii) Trolley Cars iii) Electric Locomotives

Q16. Line and phase relation of electrical quantities in star connection.

Ans:- Vph=VL/√3

Iph=IL

Q17. Which type of motor is basically used for ceiling fan?

Ans:-Capacitor start and run single phase induction motor is used for ceiling fan.

CHAPTER-6

WIRING AND POWER BILLING

Q1.Name types of wiring.

Ans. 1. Cleat wiring

2.Wooden casing and capping wiring

3.C.T.S. or batton wiring

4.Lead sheathed or metal sheathed wiring

5.Surface conduit wiring

6. Concealed conduit wiring

Q2. Which wiring is used for temporary purpose?

Ans:- Cleat wiring is used for temporary purpose

Q3. Use of fuse.

Ans:- A fuse is a short piece of metal, inserted in the circuit , which melts when excessive current flows through it and thus breaks the circuit.

Q4. List out the basic protective devices used in house hold wiring.

Ans. The basic protective devices used in house hold wiring are fuse and Miniature Circuit Breaker

Q5. Define power and its unit.

Ans. Power is the rate of doing work its unit is Watt or Kwatt.

Q6. Define Energy.

Ans. Energy is the capacity of doing work. The amount of power consumed for a certain period

of time

Q7. 1Kwhr is how much unit?

Ans. 1Kwhr is one unit.

Q8. Write down the advantages of conceal wiring.

Ans.1. There is no risk of mechanical injury

2. This wiring seems good and beautiful

3. There is no risk of electric shock

4. Durable and have a long life

5. The is no risk of fire

CHAPTER-7

MEASURING INSTRUMENT

GROUP-A

Q1. What is damping torque?

Ans:- The function of the damping device is to produce a damping force while the moving system is in motion. The damping force should be such that the pointer of the moving system comes to its final steady state value quickly without any oscillation.

Q2. What is creeping?

Ans:- It is the phenomenon in which the energy meter still shows some minimal energy consumption when there is no load attached to the meter.

Q3. Draw the connection diagram of single phase wattmeter.

Ans.

Q4. Draw the connection diagram of energy meter.

Ans.

Q5. What is the function of controlling torque in indicating instrument?

Ans. The function of controlling torque is to produces a force equal and opposite to the deflecting force, so that pointer deflects to a definite position of a particular magnitude of current.

Q6. What are the methods of damping used in measuring instrument?

Ans. The damping methods are Air friction damping, Eddy current damping, Fluid friction damping.

CHAPTER-8

INTRODUCTION OF RENEWABLE POWER GENERATION

GROUP-A

Q1. What is renewable source of energy & what are they?

Ans. Renewable energy sources are those which are renewed at least as quickly as they are consumed. They are solar energy, Wind energy and Tidal energy etc.

Q2. What are the two methods of generation in solar power plant?

Ans. 1. Conventional boiler method

2. Direct conversion method.

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