Electrical Engineering

   Resistor is a fundamental passive element. The  resistor  is  a circuit  component whose principle  property is  to oppose  the flow of current  through  it . Resistance  is represented by the letter "R". The symbol of the resistance is shown in below figure. Units for resistance is shown in below figure           A conductor is said to have resistance of  1  ohm , if   it  permits  one  Ampere   of current  to flow  through  it when  1 Volt is applied  across  it's  terminals.                 For conductors such as metals ,the resistance  is  very  low . This  is  due to the presence  of  free  electrons  in their atoms. For insulators  the  resistance  is very  high and for  semiconductors  the resistance lies in between that of metal and insulator.        The resistance R of a conductor depends on the following factors .  1) It is directly proportional to length of the conductor  2) It is inversely proportional to area of cross section of t

CAPACITORS :- 1. Air capacitors are generally available in the range (a) 10 to 400 pF (b) 1 to 20 pF (c) 100 to 900 pF (d) 20 to 100 pF Ans: a 2. The unit of capacitance is (a) henry (b) ohm (c) farad (d) farad/m Ans: c 3. The power dissipated in a pure capacitor is (a) zero (b) proportional to value of capacitance  (c) proportional to applied voltage (d) both (b) and (c) above Ans: a 4. Which of the following materials has the highest value of dielectric constant? (a) Glass (b) Vacuum (c) Ceramics (d) Oil Ans: c 5. In a capacitor the electric charge is stored in (a) metal plates (b) dielectric (c) both (a) and (b) (d) none of the above Ans: b

1.Electric pressure is also called (a) resistance (b) power (c) voltage (d) energy Ans: a 2. In the case of direct current (a) magnitude and direction of current remains constant (b) magnitude and direction of current changes with time (c) magnitude of current changes with time (d) magnitude of current remains constant Ans: a 3. Cells are connected in series in order to increase the (a) current capacity (b) life of the cells (c) voltage rating (d) terminal voltage Ans: c 4. Heat in a conductor is produced on the passage of electric current due to (a) reactance (b) capacitance (c) impedance (d) resistance Ans: d 5. The resistance of a conductor having length l area of cross section a and resistivity ρ is given (a.) ρa/l (b) ρl/a (c) ρla (d) l/ρ Ans: b 6. If a wire conductor of 2 ohms resistance is doubled in length, its resistance becomes (a) 4 ohms (b) 6 ohms (c) 8 ohms (d) 10 ohms Ans: a 7. Conductance : mho :: (a) resistance :

1. If one of the resistors in a parallel circuit is removed, the total resistance (a) decreases. (b) increases. (c) remains the same. (d) doubles. 2. When number of capacitors are connected in series, then the equivalent capacitance is (a) increases. (b) decreases. (c) remain same. (d) none of the above. 3. When number of inductors are connected in series, then equivalent inductance is (a) decreasing. (b) increases. (c) remain same. (d) none of the above. 4. An inductor is a device which store energy in the form of (a) electric field. (b) magnetic field. (c) both electric and magnetic field. (d) voltage and current. 5. A capacitor is a device designed to store energy in the (a) electric field. (b) magnetic field. (c) both electric and magnetic field. (d) plates.

1. The conductivity of superconductor is (a) infinite. (b) very large. (c) very small. (d) zero. 2. The fuse wire is made of (a) copper. (b) nichrome. (c) lead tin alloy. (d) aluminium. 3. The temperature co-efficient of resistance of semiconductor is (a) negative. (b) zero. (c) positive. (d) none of these. 4. An electric filament bulb can be worked from (a) D.C. supply only. (b) A.C. supply only. (c) Battery supply only. (d) All of the above.  5. The fuse wire is always rated in term of (a) ampere-hours. (b) ampere-volts. (c) kWh. (d) amperes.                      Comment Your Answers                             👍Share it to your friends👍

1. The filament of an electric bulb is made of (a) nichrom. (b) aluminium. (c) tungsten. (d) nickel. 2. Capacitors for P.f correction are rated in (a) KW. (b) KVA. (c) KV. (d) KVAR. 3. A 4 ohm resistor having  3 A current will dissipate the power of (a) 36 watts. (b) 10 watts. (c) 12 watts. (d) 15 watts.  4. The power factor of an inductive load is always (a) positive. (b) zero. (c) negative. (d) unity. 5. No current flows between two charged bodies if they have same (d) charge. (b) capacity. (c) potential. (d) resitance.                      Comment Your Answers                             👍Share it to your friends👍

1. An electric current is the (A) flow of electrons. (B) opposition to electrons. (C) storage of charge. (D) ionization of atom. 2. Electric pressure is also called (A) resistance. (B) power. (C) voltage. (D) energy. 3. Which of the following is best conductor of electricity? (A) aluminum. (B) silver. (C) copper. (D) gold. 4. The dielectric material used in variable capacitor is generally (A) mica. (B) air. (C) ceramic. (D) electrolyte.  5. What does a capacitor store? (A) Current. (B) Charge. (C) Voltage. (D) Power.                                      Comment Your Answers                             👍Share it to your friends👍                

1. Power consumed in a pure inductive circuit is (A) zero. (B) less. (C) high. (D) infinity. 2. A capacitor block (A) DC. (B) AC. (C) both AC or DC. (D) none of the above. 3. An inductor blocks (A) AC. (B) DC. (C) both AC or DC. (D) none of the above. 4. Frequency of direct current is (A) zero. (B) unity. (C) 50 Hz. (D) infinity 5. Power factor of direct current is (A) zero. (B) lagging. (C) unity. (D) leading.                     Comment Your Answers                             👍Share it to your friends👍

1. The number of cycle per second is called (A) frequency. (B) time period. (C) angular displacement. (D) angular velocity. 2. An instrument which detects electric current is known as (A) induction meter. (B) watt meter. (C) galvanometer. (D) none of these. 3. The substances which have a large number of free electrons and offer a low resistance are called (A) insulators. (B) inductors. (C) conductors. (D) semi-conductors. 4. The property of a conductor due to which it passes current is called (A) reluctance. (B) conductance. (C) admittance. (D) inductance. 5. Reciprocal of the conductance is called (A) admittance. (B) resistance. (C) reluctance. (D) reactance.                     Comment Your Answers                               👍Share it to your friends👍

QUESTIONS   ON   CIRCUITS 1)A network contains linear resistors and ideal voltage sources.If values of all the resistors are doubled then the voltage across each resistor A)Halved B)Doubled C)Increase four times D)Not changed 2)An Ideal voltage source will charge an ideal capacitor A)In finite time B) Exponentially C) Instantaneously D)None of the above 3) A practical current source is usually represented by A)A resistance in series with an ideal current source B)A resistance in parallel with an ideal current source C)A resistance in parallel with an ideal voltage source D)None of the above 4)In figure.1 the value of R is A)10 ohms B)18 ohms C)24 ohms D)12 ohms 5)The resistance R looking into the terminals AB in the below figure is A)2 ohms B)3.5 ohms C)2.5 ohms D)1 ohm                 Comment your answers                         👍Share it to your friends👍

QUESTIONS ON DC MACHINE CONSTRUCTION Q.1. Why is armature core of a dc machine laminated  ? Ans. To reduce Eddy current loss. Q.2. What is function of armature in a dc generator ? Ans. The function of armature is to rotate the conductors in a uniform magnetic field and provide a path of very low reluctance to the magnetic flux. Q.3. Why is the air gap between the pole -pieces and the armature kept very small ? Ans. To reduce reluctance of the magnetic path. Q.4. What is best suited material for Commutator segments? Ans. Sivered copper containing about  0.05% silver. Q.5. What for brushes are employed in dc machines ? Ans. The brushes are employed to collect current from Commutator and supply it to the external load circuit. Q.6. Why are the graphite or carbon brushes preferred over copper brushes for use in dc machines? Ans. Due to self lubricating property. Q.7. Why are brushes staggered ? Ans. The brushes are staggered in order to prevent

WHICH MATERIALS USED IN MACHINE PARTS  ???? Question : What are the materials used for the following parts of a dc machine,explain their functions. 1)Rotor core  2)Commutator bars 3)Yoke 4)Brushes 5)Pole shoes Answers :- 1)ROTOR CORE Rotor core is made from high permeability silicon steel stampings .It's function is to provide a path of very low reluctance to the magnetic flux. 2) COMMUTATOR BARS Commutator bars are built up of hard drawn copper or drop forged copper. The main function of Commutator are :               (a)It provides the electrical connections between the rotating armature coils and the stationary external circuit.              (b)As the armature rotates ,it performs a switching action reversing the electrical connections between the external circuit and each armature coil in turn so that the armature coil voltages add together and result in a dc output voltage.               (c)It also keeps the rotor or armatu

THE    COLOUR   CODE   :-           The resistance value of many resistors can  be  determined  by reading  a  series  of colour   band   printed  on   the  resistor   as shown  in   above   figure.  The   scheme   of finding the resistance value is called colour code.                The first three bands of the colour code are used  specify the  resistance  value  and the fourth band is to  specify the  tolerance. For easy understanding of this colour code concept by using a sentence as shown below. B.B. ROY of Great Britain has a Very Good Wife The capital letters of each word indicatescolour as shown below . Consider an example we can find the digits  are  1  and  0   respectively.   Therefore   the numerical    value   of the resistor is 10.  The third band tells us the power of 10 by which the first two digits are multiplied. Since the third band is orange and the corresponding digit is 3,  we multiply   10 with  10^3 which gives us a value o

Problem on circuit theory Find all branch currents, branch voltages and power dissipated in each resistor for the circuit shown in figure 1.189 . Solution :- From figure 1.190 . we can find Rx=(8+4)||6      =12||6      =(12×6)/(12+6)      =4 ohms Ry=(Rx+12)||9      =16||9      =(16×9)/(16+9)      =5.76 ohms Req=18+Ry=18+5.76= 23.76 ohms Current, I =50/Req= 50/23.76 = 2.104 A The branch current, I1=I×(12+Rx)/9+12+Rx     = (2.102 )(16)/(21+4)= 1.3468 A The branch current, I2=I×(9)/(9+12+Rx)     = (2.104 )(9)/(21+4)= 0.7575 A The branch current, I3=(I2)(8+4)/(8+4+6)     = (0.7575 ) (12)/18 = 0.505 A The branch current, I4=(I2)(6)/(8+4+6)= 0.2525 A The voltage across 18 ohms resistance, V18=(I)(18)= (2.104 )(18)= 37.878 V The power dissipated in 18 ohms resistance P18=I^2(R)= (2.104 )^2(18)= 79.711 W The voltage across 9 ohms resistance, V9 =(I1)(9)= (1.3468 )(9)= 12.1212 V The power dissipated, P9=(I1)

DC machines - 1 Q.1. What is the nature (Shape) of the dc armature mmg waveform ? Ans: Triangular Q.2. What is the nature (Shape) of air gap flux distribution in space at no load in dc machine ? Ans: Flat Tapped Q.3. What is armature reaction ? Ans : Armature reaction is the effect of magnetic field set up by the armature current on the distribution of flux under the main poles of a dc machine. Q.4. What are the two unwanted effects of armature reaction ? Ans : Demagnetisation or weakening of main field and cross - magnetisation or distortion of field. Q.5. Differentiate between geometrical neutral axis and magnetic neutral axis . Ans : Geometrical neutral axis is the axis between the magnetic poles and magnetic neutral axis is along zero magnetic field. Q.6. Define magnetic neutral plane (MNP)  ? Ans : A plane through the axis , along which no emf is induced in the armature conductors,is known as magnetic neutral plane. Q.7. In dc machine ,alon

Parallel Operation of transformer and auto transformer 1)Two Transformers operating in parallel will share the load depending upon their a) ratings. b) leakage reactance. c) efficiency. d)per unit impedance. Ans :(d) 2)In an auto-tranformer, power is transferred,through a) conduction process only. b) induction process only. c)both conduction and induction processes. d) mutual coupling. 3)Two Transformers,with equal rating and negligible excitation current, connected in parallel,share the load in the ratio of their kVA ratings only,if their pu impedances (based on their own kVA) are a)equal. b)in the inverse ratio of their ratings. c)in the direct ratio of their ratings. d)pure reactive. Ans : (a) 4)Scott connections are used for a)single - phase to three - phase transformation. b)three - phase to single - phase transformation. c)three - phase to two - phase transformation. d)three - phase to six - phase transformation. Ans :(c) 5)In Scott connection, i

Basic Questions on Transformers 1)The basic function of a transformer is to change the (a)level of the voltage (b)power level (c)power factor (d) frequency 2)The flux created by the current flowing through the primary winding induces emf in  (a) primary winding only (b) secondary winding only (c)ttransformer core only (d)both primary and secondary windings 3)The iron core in the transformer provides a_______ path to the main flux. (a)low reluctance (b)high reluctance (c)low resistance (d)high conductivity 4)For an Ideal transformer the windings should have  (a) maximum resistance on primary side and least resistance on secondary side. (b)least resistance on primary side and maximum resistance on secondary side. (c)equal resistance on primary and secondary sides. (d)no ohmic resistance on either side. 5)For an Ideal transformer shown in the below figure (a) V1=nV2, I2=-nI1 (b) V2=nV1, I2=-nI1 (c) V1=nV2, I2=(1/n)I2 (d) V1=nV

Introduction:-                 The application of scientific and  mathematical  principles  to practical ends  such  as  the design ,    manufacturer ,machine processes and  systems is known as Engineering.The  branch of Engineering Science that studies  the uses  of electricity and the electric   phenomena is  known as ELECTRICAL   ENGINEERING.It is a broad field that  encompasses  many   subfields including  those  that  deal  with   power, control   system ,   electronics   and telecommunication engineering.       Electrical Engineering is considered to deal the problems   associated  with large scale  electrical   systems  such as   power generation and motor control.    Whereas electronics engineering deals with the study of small  scale  electronic system  including semiconductors and integrated circuits (ICs).