Current Electricity Objective Questions PDF

Current Electricity 1. What are the minimum requirements to cause the flow of current? A. A voltage source, an ammeter, a conductor and insulator B. A voltage source, a switch and a resistor C. A voltage source and a conductor D. A voltage source a conductor an insulator 2. Out of the following , select the best conductor of electricity A. Graphite B. China clay C. Porcelain D. None of these 3. Which of the following statements is correct? A. The resistance does not play an important role in electrical engineering B. The resistance of the wire does not depend upon its material C. The resistance of most of the materials is independent of the temperature D. The resistance of conductor is the hindrance by which the conductor oppose the flow of current 4. Resistance of the conductor increases when A. Its length increases B. Its area decreases C. Both area and length increases D. Specific resistance is kept constant 5. The specific resistance depend upon A. The area of cross section and the length of the conductor B. The material of the conductor, its area of the cross section and length C. The nature of the material of the conductor only D. The area of the cross-section of the conductor 6. The specific resistance is defined as A. Resistance of a conductor which has length of 1 m and cross sectional area of 1 m 2 at 250 C B. Resistance of any conductor 250 C C. Resistance of any conductor at 200 C D. Resistance of a conductor which has a length of 1m and a cross-sectional at 1 cm 2 at 250 C 7. The resistance of a conductor, when its temperature is increased A. Remain constant B. Increases C. Varies D. Decreases 1 8. It was experimentally found by James Precott Joule that the heat produced in a current carrying conductor is proportional to A. The square of the current B. Square of the resistance C. The current D. Inversely proportional to time 9. The value of Joule’s mechanical equivalent of heat ,J, is equals to A. 4.2 calories/Joule B. 2.4 Joules/calorie C. 4.2 Joules/calorie D. 4.2 Joules 10. Temperature coefficient of a conductor is defined as the A. increases in resistance per ohm per degree centigrade B. increase in resistance per degree centigrade C. increase in resistance per degree absolute D. decrease in resistance per ohm per degree centigrade 11. When current flows in a conductor, heat is produce because A. heat is proportional to the square of the current B. of electronic collision C. of inter-atomic collision D. of Joule’s law 12. Heating effect of current has undesirable side effect. A. electric oven B. electric iron C. immersion heater D. vacuum cleaner 13. The resistance of the carbon when its filament temperature is decreased A. increases B. decreases C. remains same D. increases enormously 14. The curve representing ohm’s law is A. a parabola B. linear C. sine function D. a hyperbola 15. The condition in Ohm’s law is that A. ratio of V/I should be constant B. Current should be proportional to voltage C. The temperature should remain constants D. The temperature should vary 2 16. Ohm’s law does not apply to A. conductors B. conductors when there is change in temperature C. semi-conductor D. ac circuit 17. Ohm laws is applicable to A. electric arc B. rectifying devices C. gas discharge lamps D. none of the above 18. Ohm’s law can be applied with certain reservations to A. rectifying devices B. semi conductors C. electrolytes D. none of the above 19. The presence of an electric current is made known by A. flashing B. effects produced C. cracking D. electric shock 20. An electric current can neither be ____nor____ A. felt, seen B. seen, touched C. seen, produced any effect D. produced and felt 21. The presence of the current is only made known by the effect it produces. Three important effects are. A. Heating, electric shock and generation B. generation, chemical and electric shock C. heating, magnetic and electric shock D. heating, magnetic and chemical 22. Voltage applied across a circuit, acts as A. mass of electrons B. negative ions C. A component of current D. a force 23. A variable resistance is connected across constant voltage E volts. The value of the resistance is gradually increased. The graph which shows relationship between current I and resistance R is A. 3 B. C. D. 24. In a series circuit the current is A. constant B. zero always C. proportional to the resistance D. different in different resistors 25. In a parallel circuit the potential difference across the resistance A. varies B. is different from the applied voltage C. is sometimes constant D. is always constant 26. The resistance R1 and R2 connected in parallel. The ratio of values of R1:R2 is 4:1, The current in R1:R2 will be equal to A. 1:4 C. 1:4 B. 1:1 D. 4:4 27. In a circuit that consist of parallel 12V source and flows a current of 10 A in each branch A. The total voltage is 24V B. The total voltage is zero C. The arrangement can be loaded up to 10 A maximum D. The voltage sources connected in parallel can supply a maximum current of 20 A 28. In a series connection of bulb A and B in series across a source voltage, bulb B glows brighter because its resistance is A. In parallel with A B. In series with A C. Lower than A D. Higher than A 29. In a series circuit with two bulb A and B, and a voltage source, wherein a wire has been connected across bulb A, bulb A will A. Not glow B. Be of the same intensity of B 4 C. Glow brightly D. Be dim 30. A resistance of 4 ohms is connected across 100 V supply. When another ‘R’ ohm is connected in parallel with 4 ohm, the total current taken from the supply was found to be 50 A. The value of the resistance “R” is A. 2 ohms C. 5 ohms B. 3 ohms D. 4 ohms 31. The voltage applied across an electric press was reduced by 50%. The power consumed by the press will be reduced to A. 25% C. 60% B. 75% D. 50% 32. Two electric presses are connected in parallel. The resistance of the first is 100 ohms and that of the second is 300 ohms The total current taken by both of the presses is 4 A. The ratio of the current taken by first : second will be equal to A. 2:3 C. 3:1 B. 1:3 D. 1.2:3 33. Three resistance R1,R2 and R3 are connected in series with a 220 V supply. Voltmeter is connected across R2. If R2 becomes open-circuited the reading of the voltmeter will A. Become 220 V B. Decrease slightly C. Falls zero D. Increases slightly 34. Three elements having conductance G1,G2 and G3 are connected in parallel Their combined conductance will be A. G1+G2+G3 B. (G1G2+G2G3+G3G1)/(G1+G2+G3) C. 1 / (G1+G2+G3) D. 1/(1/ G1+1/ G2+1/ G3) 35. Four resistance R1,R2,R3 and R4 are connected in series against 220V supply. The resistance are such that R1>R2>R3>R4.The least power consumption will be in A. Resistors R1 B. Resistor R4 C. Resistor R3 D. Resistor R2 36. When the current flows through heater coil it glows but supply wiring does not glow because A. Supply wiring is covered by insulation layer B. Current through supply line flows at slower speed C. Supply wires are made of superior material D. Resistance of heater coil is more than that supply wires 37. Resistors commonly used in power circuits are A. Carbon resistor 5 B. Etched circuit resistors C. Wire wound resistors D. Deposited metal resistors 38. International ohm is defined in terms of resistance of A. A column of mercury B. A cube of carbon C. Unit length of metal wire D. A cube of copper 39. Which of the following has a negative coefficient of resistance A. Wire wound resistor B. Non-metals C. Thermistor D. Metals 40. The current carrying capacity of the fuse material depends on A. Length B. Material C. Cross-sectional area D. All of the above 41. Twelve wires of the same length and same cross-sectional area are connected in the form of a cube. If the resistance of each wire is R, then the effective resistance between symmetrical corners A and B is A. 4/3 R C. 3/4R B. R D. 5/6R ANSWERS: 1. C 16.C 31.A 2. A 17.D 32.C 3. D 18.C 33.A 4. A 19.B 34.A 5. C 20.B 35.B 6. A 21.C 36.D 7. B 22.D 37.C 8. A 23.D 38.A 9. C 24.A 39.C 10. A 25.D 40.D 11. C 26.A 41.D 12. D 27.D 13. A 28.D 14. B 29.A 15. C 30.D MAGNETISM AND ELECTROMAGNETISM 6 1. A natural magnet is called A. Street C. Magnetism B. Lodestone D. Soft Iron 2. A magnet is able to attract A. Iron ,aluminum and brass B. Iron, cobalt and zinc C. Iron, copper and nickel D. Nickel, cobalt and steel 3. Externally, magnetic line of force travel A. South to north B. North to south C. Negative to positive D. In both directions 4. A material commonly used for shielding or screening magnetism is A. Brass C. Copper B. Aluminum D. Soft Iron 5. The magnetism that remains in a magnet after magnetizing force has been removed is called A. Permeability B. Induction C. Residual D. Saturation 6. Iron become magnetized by induction when it is A. Heated B. Suspended east and west C. Near in one of the magnet D. Heated with some materials 7. Magnetic lines of force are called A. Hysteresis B. Current C. Flux D. Magneto motive force 8. The force between two magnetic poles varies with distance between them. The variation is A. In direct proportion to the distance B. In inverse proportion to the distance C. In direct proportion to the square of the distance D. In inverse proportion to the square of the distance 9. The magnetic potential in magnetic circuit can be measured in terms of A. Farads C. Coulombs B. M.M.F D. none of these 7 10. Permeance is analogous to A. Conductance B. Resistance C. Reluctance D. None of these 11. The permeability of the material means A. Strength of permanent magnet B. Strength of an electromagnet C. The magnetization left in the iron after exciting field has been removed D. The conductivity of the material for magnetic lines of force 12. When magnetic flux and the area A under its influence are known, the magnetic flux B density is given as A. B=A C. B=A/ B. B= /AD. B=A2 13. The relative permeability , is given by the A. B/(0 X H) C. 0 / U B. B/H D. 0/H 14. Relative permeability of materials is given by(K is susceptibility of the material) A. 1 + oK C. 1+( ) B. 1 +( ) D. oH 15. The relative permeability of paramagnetic substance is A. Slightly less than one B. Equal to 1 C. Slightly greater than one D. Very much greater than one 16. The value of permeability for the free space i A. 4x10-7 Hm-1 B. 4x 10-7 Hm-1 C. 4 x 107 Hm-1 D. 1/(4) x 107 Hm-1 17. The magnetization in any magnetic material appears as a result of A. Electron orbital motion B. Electron spin C. Spin of the nucleus about its axis D. All of these 18. The sum of the magnetic moments in unit volume of the solid is called A. Field strength B. Magnetization C. Permeability 8 D. Susceptibility 19. Which of the following materials does not have permanent magnet dipole A. Paramagnetic B. Antiferromagnetic C. Diamagnetic D. Ferrimagnetic 20. Interaction between the neighboring dipoles is negligible in the case of a A. Paramagnetic materials B. Diamagnetic materials C. Antiferromagnetic materials D. Ferrimagnetic materials 21. Each ferromagnetic material has characteristic temperature above which its properties are quite different from those below that temperature. This temperature is called A. Transition temperature B. Faradays temperature C. Demagnetization temperature D. Curie temperature 22. The relative permeability of iron is A. 5000 C. 3000 B. 7000 D. 1000 23. Which of the following material is used for making permanent magnets A. Carbon steel B. Platinum cobalt C. Alnico V D. All three mentioned above 24. Which of the following has the highest value of relative permeability A. Iron C. Supermalloy B. Mu-metal D. 4% Si-Fe 25. Ferrimagnetic materials generally behave as a A. Semi-conductor B. Conductor C. Insulator D. Any of the above 26. Transformers cores operating at microwave frequency ranges are generally made up of A. Ferrites B. Supermalloy ANSWERS: C. Silicon steel 1. B 15. C D. Alnico V 2. D 16. B 3. B 17. D 4. D 18. B 27. The magnetic materials which can be easily magnetized in both the directions are known as 5. C 19. C A. Soft magnetic materials 6. C 20. A B. Hard magnetic materials 7. C 21. D 8. D 22. A 9 9. B 23. D 10. A 24. C 11. D 25. A 12. B 26. A 13. A 27. A C. Low hysteresis loss materials D. High hysteresis loss materials 28. Eddy current loss can be minimized by A. Decreasing the resistance of the magnetic medium B. Increasing the resistance of the ,magnetic medium C. Decreasing the permeability of the magnetic medium D. None of the above ELECTROMAGNETIC INDUCTION 1. There are no self induce voltage in the coil when A. An ac current flows through the coil B. Current decreases from 0.1 to 0 A in 1 second C. A dc current flows through the coil D. A dc current flows through the coil 2. The self-induced of the coil is not influenced by A. The voltage applied of the coil B. The change in current C. Number of turns of the coil D. Magnetic resistance of the magnetic circuit 3. The coefficient of self-inductance of a coil is defined as A. N/ C./NI B. N/I D. I/N 4. Which of the following statement is incorrect? A. Whenever the flux linking with the coil or circuit changes, emf is produced B. The direction of the dynamically induced emf can be determined by the Flemming’s hand rule C. Coefficient of coupling for tightly coupled coil is zero D. The coefficient of self inductance is proportional to the square of number of turns on it 5. Which of the following statement about inductance of a coil is true? A. Inductance is a characteristic of coils occurring only in case of ac B. Inductance appears only if the coil has as iron core C. Inductance is only another expression for self-induced voltage D. Inductance characterizes the magnetic properties of coil which are significant for the value of self-induced voltage generated due to current change in the coil 6. A collapsing field around a coil A. Tends to oppose the decay of coil current B. Helps the decay of the coil current C. Tends to aid current flow reversal D. Does not affect the current flow 10 7. Energy stored in an inductor is given by A. 2LI2 Joules C.N/I Joules B. 0 Joules D. ½ LI2 Joules 8. Which of the following is a vector quantity? A. Magnetic potentials B. Flux density C. Magnetic field density D. Relative permeability 9. A conductor of length L has current. I passing through it, when it is place in parallel to a strong magnetic field. The force experienced by the conductor will be A. BLI C. B2LI B. Zero D. BL2I 10. Whenever a conductor cuts magnetic flux, an emf is induced in that conductor. Above statement is due to A. Joule’s law B. Coulomb’s law C. Faraday’s law D. Weber and Ewing’s theory 11. The left hand rule correlates A. Self-induction, mutual induction and direction of force on a conductor B. Magnetic field, electric field and direction of force on a conductor C. Current induced emf and direction of force on a conductor D. Current, magnetic field and direction of force on a conductor 12. In the left hand rule, thumbs always represent A. Voltage B. Current C. Direction of force on conductor D. Magnetic field 13. The coefficient of the coupling between two air core coils depend on A. Self inductance of the two coils B. Mutual inductance and between two coils C. Mutual inductance and self inductance of the two coils D. None of the above 14. While comparing magnetic and electric circuits, the flu of magnetic circuit is compared with which parameter of electric circuit? A. E.M.F. B. Current density C. Conductivity D. Current 11 15. While comparing the magnetic and electric circuits, the point of dissimilarity exists while considering A. Flux and current flow B. Permeance and conductance C. M.M.F. and e.m.f D. Reluctance and resistance 16. DC voltage is applied at the transformer primary. No voltage will be induced in a secondary coil when primary current is A. Switched on B. Switched off C. Reduced D. Constant 17. The effect of the inductance of a coil on a constant direct current is that A. It strengthens the current B. It does not affect the constant direct current C. It decreases the current D. It causes a higher voltage drop 18. The magnetic flux in the magnetic circuit can be increased by A. Increasing the MMF B. Decreasing the MMF C. Reversing the direction of current D. Making an air gap in the core 19. How can inductance of the coil can be increased? A. By increasing the current B. By thick layers of hard paper in the gap C. By connecting ohmic resistance in series D. By increasing the number of turns 20. Good smoothing factor of a coil depends on the A. Terminal voltage B. Property of the wire of the coil C. Inductance of the coil D. Cross-sectional area of the wire of the coil 21. Leakage factor is A. Less than unity B. Equal to unity C. More than unity D. Zero 22. The law that induces emf and current always opposes the cause producing them was discovered by A. Lenz B. Faraday C. Maxwell 12 D. Ohm 23. According to Len’z law the direction of the induced emf and hence current A. May be found by the right hand rule B. Always opposes the cause producing it C. Is determined by the rate of cutting flux D. May be found by the left hand rule 24. Sparking occurs when a load switched off because the circuit has high A. Capacitance B. Inductance C. Resistance D. reluctance 25. Air gap in the iron core of an inductor prevents A. Hysteresis loss B. Flux change C. Transformer action D. Core saturation 26. The growth of the current in an inductive circuit follows A. Hyperbolic laws B. Ohm’s law C. Exponential law D. Linear law 27. The time constant of an inductive circuit is defined as the ratio of A. R/L C.Lf/R B. Rf/L D.L/R 28. The time constant is the time it takes the current in an inductive circuit to rise to A. 66% of its final steady state value B. 70% of its final steady state value C. 63% of its final steady state value D. 50% of its final steady state value 29. Mutual inductance can also be defined as A. M=N2 where N2-no. of returns in the second coil B. M= N2 C. M=N2 D. M=N2 30. The mutual inductance of two coil is maximum when the coils are 13 A. Inclined at angle of 45 B. At the right angle to each other C. Facing each other D. Touching each other 31. The value of the mutual inductance in terms of self-inductance of the two coil L1 and L2 is proportional to A. L1 L2 B. L1/ L2 C. D. 32. Coupling coefficient K in terms much used in radio work , can obtained from A. K= M B. K=M C. K=M/ D. K=M L1 L2 33. The coupling coefficients denotes A. The degree of the magnetic linkage B. Whether the reluctance remains constant C. The variation of the inductance between the two coils D. Whether the flux linkage is constant 34. It is difficult to magnetize steel because it is A. Low permeability B. Higher permeability C. High permeability D. High density 35. In the electrical machines laminated cores are used with a view to reduce A. Eddy current loss B. Copper loss C. Hysteresis loss D. Stray losses 36. The area of the hysteresis loop represents hysteresis material is proportional to A. J/m3/s B. J/cycle C. J/s 37. According to the hysteresis law, hysteresis loss in a A. B 1.2 B. B 1.6 C. B 0.6 14 D. B 3.6 38. The degaussing is the process of A. Removing gasses B. Removal of magnetic impurities ANSWERS: C. Demagnetizing metallic part 1. D 16.D 31.C 2. A 17.B 32.C 39. Hysteresis losses can be reduced by 3. B 18.A 33.A A. Using grain oriented silicon 4. C 19.D 34.A B. Increasing the frequency of the field 5. D 20.C 35.A C. Laminating the core 6. A 21.C 36.A D. None of these 7. D 22.A 37.B 8. C 23.B 38.C 9. B 24.B 39.A 10. C 25.D 11. D 26.C 12. C 27.D 13. C 28.C 14. D 29.A 15. A 30.D 15 ELECTROSTATIC 1. Absolute permittivity of vacuum is taken as A. 8.854 x 10-6f/m B. 8.854 x 10-12f/m C. 8.854 x 10-9f/m D. 8.854 x 10-3f/m 2. Relative permittivity of vacuum is A. Zero B. 8.854 x 10-6 C. Unity D. 8.854 x 10-12 3. In the electric field , the potential is the work done in Joules A. To bring positive charge of 1 coulomb from infinity to that point B. To bring any charge from infinity to that point C. In moving a unit positive charge from one point to another point 4. The unit of field intensity is A. Coulomb B. Coulomb/m2 C. Newtons/Coulomb D. Newton-meter/Coulomb 5. Coulomb’s law for the force between electric charges most closely resembles with 16 A. Gauss theorem B. Newton’s law of gravitation C. Law of conservation of energy D. Newton’s law of motion 6. Dielectric strength of a material depends on A. Moisture content B. Thickness C. Temperature D. All of the above 7. What will happen to an insulating medium voltage more than the breakdown voltages applied or A. It will get punctured B. It will become magnetic C. It will melt D. Its molecular structure will change 8. Which medium has the highest value of dielectric strength A. Glass B. Mica C. Porcelain D. Quartz 9. The maximum value of potential gradient in a cable occurs in A. Outer sheet B. Insulation C. Conductor D. Uniform all over 10. A region around a stationary electric charge has A. Electric field B. Magnetic field C. Both electric and magnetic field D. Neither of the two 11. Inside a hollow spherical conductor A. Electric field is constant B. Electric field is zero C. Electric field changes with distance from the center of the sphere 12. Capacitors are said to A. Block a.c. and pass d.c. B. Block d.c and pass a.c. C. Pass a.c. and d.c. D. Block a.c. and d.c. 13. Which statement influence the capacity of a capacitor A. Area of the plates, thickness of the plates and the rate of change 17 B. Area of the plates , Dielectric and the rate of charge C. Distance between the plates, dielectric and thickness of the plates D. Distance between the plates, area of the plates and dielectric 14. What charge would be taken by a practical to 10 microfarad capacitor if connected to a 200V supply A. 20 V B. 20 A C. 20uC D. 2.0 mC 15. The effect of the dielectric is to A. Increase the capacitance B. Decrease the capacitance C. Reduce the working voltage D. Increase the distance between the plates 16. Electrolytic capacitor is the most commonly used type but it has two disadvantages A. Low insulation resistance and suitable for d.c. only B. High insulation resistance and suitable for a.c. only C. High capacitance and high insulation resistance D. High capacitance and low insulation resistance 17. In a radio a gang condenser is a type is a type of A. Air capacitor B. Paper capacitor C. Ceramic capacitor D. Electrolytic capacitor 18. A sphere of one meter radius can attain a maximum potential of A. 1000V B. 30KV C. 3 million volts D. 3kV 19. A capacitor of 100f is connected in series with a resistance of 1000 ohms. The time constant of the circuit is A. 1 second B. 0.01 second C. 0.1 second D. 0.001 second 20. The power dissipated in a pure Capacitor A. Maximum B. Minimum C. Zero D. Depends on the size of the voltage 21. In a capacitor the electric charge is stored in 18 A. Metal plates B. Dielectric C. Dielectric as well as metal plates 22. Four condensers of 4f each are connected in parallel. Their equivalent capacitance will be A. 16f B. 64f C. 4f D. 1f 23. What is the relation between the field strength E, voltage V and the distance between the parallel plates A. E=V/d B. E=Vd2 C. E=Vd D. E=V2/d 24. One farad is A. coulomb-joule B. one coulomb per volt C. joule per volt D. one volt per coulomb 25. If a dielectric is placed in an electric field , the field strength A. Decreases B. Increases C. Remains same D. Become zero 26. If a medium of a parallel plate capacitor consists of mica and air, the capacitance is increased by A. Increasing the air space B. Increasing the area of the plates C. Decreasing the thickness of mica D. Increasing the thickness of mica 27. In a parallel plate capacitor of the capacitance Co the electric field is E. If a dielectric slab with dielectric constant equal to 7 is introduced to fill capacitor completely, the electric field will become A. E/7 B. E C. E/3.5 D. 7E 28. In a parallel plate capacitor of the capacitance Co the electric field is E. If a dielectric slab with dielectric constant equal to 7 is introduced to fill capacitor completely, capacitance will become A. Co B. Co/7 19 C. 7Co D. Co/3.5 29. In a parallel plate capacitor of the capacitance Co the electric field is E. If a dielectric slab with dielectric constant equal to 7 is introduced to fill capacitor completely, induced surface charge will be A. q/7 B. 7q C. 7q/6 D. 6q/7 30. A capacitor having a capacitance of 30f is connected across 200Vdc source. The charging current will be least A. When the capacitor is half charged B. Initially C. When capacitor is fully charged D. When capacitor is almost 75% charged 31. A capacitance C is charged through resistance R. The time constant of the charging circuit is given by A. RC B. 1/RC C. C/R D. R/C 32. A circuit component that opposes the change in the circuit voltage is A. Resistance B. Inductance C. Capacitance D. None of the above 33. In a capacitor, the electric charge is stored in A. Metal plates B. Dielectric C. Dielectric as well as metal plates D. Neither dielectric nor metal plates 34. Internal heating of capacitor is usually attributed to A. Leakage resistance B. Electron movement C. Plate vibration D. Dielectric charge 35. The ohmmeter reading for a shorted capacitor is A. Infinity B. Few kilo ohm C. Few mega ohms D. Zero 20 ANSWERS: 1. B 16.D 31.A 2. C 17.A 32.C 3. A 18.D 33.B 4. C 19.C 34.A 5. B 20.C 35.C 6. D 21.B 7. A 22.A 8. B 23.A 9. C 24.B 10. A 25.A 11. B 26.B 12. B 27.A 13. C 28.C 14. D 29.D 15. C 30.C ELECTROLYSIS AND STORAGE BATTERY 1. Electro-chemical equivalent is A. Ratio of atomic weight of an element to atomic weight of hydrogen B. Mass of the element liberated per unit of quantity of hydrogen C. Ratio of atomic weight of valency 2. The mass of material deposited over an electrode is A. Proportional to the voltage B. Proportional to time voltage C. Proportional to the current only D. Proportional to the quantity of electricity and electro-chemical equivalent 3. For all substances A. 9650 coulombs B. 96500 coulombs C. 965 coulombs 21 D. 96.5 coulombs 4. The mass of an ion liberated at an electrode is directly proportional to the quantity of electricity which passes through the electrolyte. The above statement is associated to A. Gauss’s theorem B. Laplace law C. Weber and Ewing’s theory D. Laws of electrolysis 5. In electroplating, the positive electrode is called A. cathode B. terminal C. anode D. ion trap 6. Impurities in an electrolyte can cause an internal short circuit condition called A. Depolarization B. Electrolysis C. Local action D. Polarization 7. Distilled or approved water is used in electrolyte because it A. Prevents or slows down local action B. Speeds up electrochemical action C. Improves specific gravity D. Prevents polarization 8. The condition of a liquid electrolyte is measured in term of its A. Current value B. Specific gravity C. Acid content D. Voltage output 9. One factor affecting the voltages of the primary cell is the A. Area of the plates B. Distance between the plates C. Type of plates and electrolytes D. Thickness of the plates 10. Local action in the primary cell can be rectified by A. Charging the cell B. Amalgamating the zinc electrode with the mercury C. Using the cell for just few minutes D. Dry cell 11. The action of the dry cell is to change A. Chemical action to mechanical energy B. Chemical action to chemical energy C. Electrical energy into mechanical energy 22 D. Electrical energy into magnetic energy 12. Polarization in dry cell can be got rid of by A. Coating the electrode of the cell B. Chemical means C. Discharging the cell D. Disposing the cell 13. The two main defects of the primary cell are A. Polarization and sulphation B. Local action and polarization C. Buckling and polarization D. Suphation and buckling 14. The average dry cell gives an approximate voltage of A. 1.3 V B. 1.5 V C. 1.1 V D. 1.7 V 15. To obtain a high voltage of about 1.9 V from a dry cell one would use A. Western standard cell B. leclanche cell C. Nickel-Cadmium cell D. Magnesium cell 16. The advantage of a dry cell is that A. It gives more emf that a wet cell B. It can be stored indefinitely C. its internal resistance is low compared to wet cell D. It needs no depolarizer 17. Wet cell is preferred to a dry cell because A. Its corrosion is small B. Its internal resistance is high C. Its polarizes continuously D. it has higher emf 18. Lechanche cell is most suited for A. continuous work B. intermittent work C. where large current is required D. where large voltage is required 19. When cells oh each emf E volts, and internal resistance r ohms are connected in series, the current I through an external resistance R ohms is given by A. I = E / (R + r/n) B. I = E / (R + r) 23 C. I = nE / (R + nr) D. I = E / (r + nR) 20. When n cells each of emf E volts and internal resistance r ohms are connected in parallel, the strength of the current is given by A. E / (R + r/n) B. nE / (r + R) C. E / (n +Rr) D. E / (R + n/r) 21. Cells are connected in parallel to A. increase the internal resistance B. decrease the current capacity C. increase the current capacity D. increase the voltage output 22. Cells are connected in series to A. decrease the voltage output B. increase the voltage output C. decrease the internal resistance D. increase the current capacity 23. The maximum voltage that is supplied by an ordinary cells is A. approx 0.5 V B. approx 1.5 V C. approx 1.11 V D. approx 1.74 V 24. The function of the depolarizer in carbon zinc cell is that A. it converts the produced hydrogen into water B. it prevents the fast chemical action on zinc container C. it synthesizes the composed electrolyte D. it absorbs the oxygen produced in the cell 25. Which of the following acts are depolarizers in dry cell? A. Manganese dioxide B. Zinc chloride C. Ammonium chloride D. Carbon powder 26. One advantage of a secondary cell is that it A. can be recharge B. can be used for portable equipment C. it is compact, easy to carry D. cannot be recharge 27. The composition of a secondary cell is A. zinc, copper and dilute sulfuric acid 24 B. zinc, carbon and dilute sulfuric acid C. lead, lead peroxide and dilute sulfuric acid 28. Nickel-cadmium dry cell is becoming popular in power supplies to electronic calculators because A. it has a standard shape B. it is dry C. it is rechargeable D. it is easily manufactured 29. Secondary cell can produced large amounts of power for a A. short time and can be recharged B. long time and can be recharged C. short time and cannot be recharged D. long time and cannot be recharged 30. Gassing occurs in the process of A. charging an accumulator B. charging a dry cell C. discharging an accumulator D. discharging a dry cell 31. The condition of a secondary cell can be determined by A. its terminal voltage B. the color of the electrolyte C. level the electrolyte D. the terminal voltage and strength of the electrolyte 32. The lead acid accumulator should be recharged when the specific gravity of the electrolyte is about A. 1.15 C. 1.80 B. 1.25 D. 1.35 33. Others types of accumulator besides the leads acid type are A. alkaline batteries only B. alkaline and solar batteries C. alkaline and dry batteries D. nickel-cadmium batteries 34. Electrolyte of a storage battery is formed by adding A. water to hydrochloric acid B. sulfuric acid to water C. hydrochloric acid to water D. water to sulfuric acid 35. When the electrolyte of a storage battery is low it is usually proper to A. add a special weak acid solution B. top up with distilled water C. charge the battery for a short time before adding an electrolyte D. drain the battery completely fill it with fresh electrolyte 25 36. The ampere hour capacity of battery depends on A. the thickness of the plates B. the area of the plates C. the strength of the electrolyte D. the distance between the plates 37. A 60 ampere-hour battery has 6 ampere discharge rates. it will provide a current of A. 10 amperes for 6 hours B. 6 amperes for 10 hours C. 12 amperes for 5 hours D. 20 amperes for 3 hours 38. To keep the terminals of a lead acid Storage battery free from corrosion, it is advisable to A. clean the terminals frequently B. charge for battery at frequent intervals C. keep the electrolyte level low D. apply petroleum jelly 39. The internal resistance of a discharge battery A. is more B. is less C. remains the same D. is negative 40. it is not desirable to leave a lead storage battery in discharge state for a long time mainly because A. electrolyte will attack the container B. plates will become sulfated C. electrolyte will become weak D. acid will evaporate 41. A partially discharged lead storage battery may be brought back to full charge by A. adding sulfuric acid B. adding distilled water C. applying a.c. voltage across the terminals D. applying d.c. voltage across the terminals 42. Which of the following is a primary cell A. Mercury oxide B. Lead acid C. Nickel-iron-alkaline D. Nickel-cadmium-alkaline 43. Charging a lead-acid causes the electrolyte to become A. stronger C. weaker B. stable D. water 44. Separators in storage battery cells are designed to prevent the plate from 26 A. touching the electrolyte B. touching the container C. shorting together D. shorting to the sediment 45. Which of the following affect the capacity of lead-acid battery? A. Temperature B. Specific gravity C. Discharge time D. All of the above 46. During the charging period of a lead-acid battery, the charging rate is lowered to prevent violent gassing because A. the gasses given off are explosive B. evaporation of the electrolyte will weaken its effect C. the cells will be subjected to excessive pressure D. violent gassing tends to wash the active material from the plate 47. A fuel cell converts___________ energy in electrical energy A. mechanical B. magnetic C. chemical D. solar 48. A cell which is used as voltage reference source for instrument calibration is A. solar cells B. battery cells C. mercury-cadmium cells D. nickel-cadmium cells 49. The advantage of the iron-nickel battery over the lead-acid battery is that A. it has a much higher efficiency B. it needs less maintenance C. the cell voltage of the iron-nickel battery is higher D. it is much cheaper 50. While charging accumulator, one should A. check the acid level with a lighted match B. short the cell to see if they are fully charge C. keep in well ventilated space ANSWERS: D. connect and disconnect them with the supply 1. B 16. 31. D 46.D 2. D 17. 32. A 47.C 3. B 18. 33. D 48.C 4. D 19.C 34.B 49.B 5. C 20.A 35.B 50.C 6. C 21.C 36.B 7. A 22.B 37.B 8. B 23.B 38.C 9. C 24.A 39.A 10. B 25.A 40.B 27 11. B 26.A 41.D 12. B 27.C 42.A 13. B 28.C 43.A 14. B 29.A 44.C DC GENERATOR 1. The output voltage of a single loop generator is a A. Steady d.c. B. Steady a.c. C. Pulsating a.c. D. Pulsating d.c. 2. A smooth output from a generator is obtained by a A. design of the armature winding B. changing the form of the commutator C. changing the field strength 3. The output voltage of a generator is given by the equation is A. E = V – IaRa B. E = V + IaRa C. E = Ldi/dt D. E = -Nd/dt 4. What effect on current flow does reversing the direction of movement conductor in the magnetic field of a generator have A. neutralize the current flows B. has no effect on current C. it reverse the direction of current flow 5. In most generators the output voltage is induced by A. rotating magnetic field past stationary coils B. relative motion between the field and the armature coil C. converting electrical energy into mechanical energy 6. How would you determine, from visual observation of the armature winding, whether the generator is lap or wave wound A. connection to the field winding B. connection to commutator C. connection to the brushes D. the direction of the end connection 28 7. What is the classification if given to a d.c. generators that receives its field excitation current from internal source? A. self-excited excitation B. controlled excitation C. separately excited D. internally excited 8. The shunt field of a compound generator is connected across both the series field and the armature. This connection is known as A. short shunt B. long shunt C. differential compound D. cumulative compound 9. For all symbols having their usual meaning, the emf generated in the lap winding is given by A. B. C. D. 10. Residual magnetism is necessary in a A. separately excited generator B. self excited generator C. both of these D. none of these 11. If the number of poles in a lap wounded generator is increase by a factor of 2 generated emf will A. remains the same B. increase by a factor of 2 C. decrease by a factor of 2 D. increase by a factor 4 12. Electric dc generators have normally, an overall efficiency of the order of A. 60 – 80% C. 80 - 90% B. 75 – 85% D. 85 – 95% 13. The armature magnetic field has effect that A. it demagnetizes or weakens the main flux B. its cross magnetizes, or distorts it C. it magnetizes or strengthens the main flux D. (A) and (B) 29 14. Brushes are always placed along A. magnetic neutral axis (MNA) B. Geometric neutral axis (GNA) C. perpendicular to MNA D. perpendicular to GNA 15. MNA makes an angle of ____ with the flux passing through the armature A. 0 C. 45 B. 90 D. 180 16. In a dc generator flux is seen to be___ at the trailing pole tips and also ___ at the leading pole tips A. weakened, weakened B. weakened, crowded C. crowded, weakened D. same, same 17. If is the forward lead angle in radians, Z is the total number of conductors and I is the current in each armature pole, the demagnetizing ampere turns/pole are given as A. B. C. D. none of these 18. Which of the following curve A. A B. B I A D C. C B D. D C LOAD CURRENT 19. The function of a compensating winding is to neutralize the A. reactance voltage generated and consequence of commutation B. cross magnetize the effect of armature reaction C. demagnetizing effect of armature reaction D. all of these 20. In a commutation process it is the A. current which is getting reversed B. voltage which is getting reversed C. both of these D. none of these 21. In any dc generator the emf generated in the armature is maximum when 30 A. rate of change of flux is minimum B. rate of change of the flux is maximum C. flux linked with the conductor is maximum D. flux linked with the conductor is minimum 22. A simple method of increasing the voltage of an dc generator is A. to decrease the air gap flux density B. to increase the speed of the rotation C. to decrease the speed of the rotation D. to increase the length of the armature 23. The method which can be used to improved commutation process is A. increasing the resistance of the brushes B. reducing the number of turns in the armature coil and hence the number of segment in the commutator C. to neutralize the reactance voltage by producing a reversing emf in the short circuit coil under commutation D. all of the above 24. The function of the interpole or compole is A. to neutralize the reactance of the voltage and help in commutation process B. to neutralize the cross-magnetizing effect of the armature reaction C. to neutralize the demagnetizing effect of the armature D. (A) and (B) 25. Interpoles are connected ____ with the armature and compensating windings are connected in _______ with the armature A. series, series B. shunt, series C. series, shunt D. shunt, shunt 26. The function of the equalizer ring is A. to avoid unequal distribution of current at the brushes B. to help to get sparkless commutation C. both of these D. none of the above 27. Maximum number of equalizer rings needed in electrical machine is equal to A. N = B. N = C. N = D. none of these 31 28. Generators are often preferred to be run in parallel because of having of the advantage of A. great reliability B. generator efficiency C. meeting greater load demands D. all of the above 29. Which of the following is most suitable for running in parallel operations A. shunt generator B. series generator C. compound generator D. all of these are equally suitable 30. Which of the following characteristic will be preferred for parallel operation of two alternators A. A B. B C. C D. D 31. External characteristics of d.c. generators can be obtained by A. internal characteristics B. no load saturation characteristics C. armature resistance drop D. both A and B 32. Which of the following characteristics of self-excited dc generators A. A B. B C. C D. D 33. Critical resistance of a dc generators Rc A. Rc inversely proportional to the speed B. Rc proportional to the speed C. Rc proportional to the square of the speed D. Rc inversely proportional to the square of the speed 34. Shunt generators are used where the main requirement is constant A. current and voltage B. current C. voltage over wide load range D. voltage over a narrow load range 35. Equalizer connection are required when paralleling two A. compound generator B. series generator C. shunt generator D. batteries 32 36. The function of an interpole is A. neutralize cross field of armature reaction and obtain ideal commutation B. increase the armature reaction and thus obtain ideal commutation C. neutralize cross field of the armature and thus obtain under commutation 37. Interpoles are normally connected in A. parallel with the field B. in series with the field C. parallel with the load D. series with the load 38. In DC generators, lap winding is used for A. low voltage, low current B. high voltage, high current C. low voltage, high current D. high voltage , low current 39. DC generators preferred for charging automobile batteries is A. shunt generator B. series generator C. long shunt compound generator 40. Which of the following component of a dc generator plays vital role for providing a direct current of a dc generator A. dummy coils B. equalizer ring C. eye bolt D. commutator 41. In dc generator the ripples in the direct emf and generated are induced by A. using equalizer ring B. using commutator with large number of segment C. using carbon brushes with superior quality 42. which of the following generators are preferred for parallel operations A. series generators B. shunt generators C. compound generators 43. Full load efficiency of the generator will be A. 68.5% C. 80.8% B. 73.5% D. 92.51% 44. Which loss in the generator varies with the load A. copper loss B. eddy current loss C. hysteresis loss D. windage loss 33 45. In dc generator, the cause of rapid brush wear may be A. imperfect contact B. sever sparkling C. rough commutator surface D. any of the above 46. In the shunt generator the voltage built up generally restricted by A. speed limitation B. armature heating C. saturation of iron 47. The armature of a dc generator is laminated to A. reduce the bulk B. insulate the core C. reduce the eddy current loss D. provide passage for cooling air 48. Which of the following helps reducing the effect of armature reaction in dc generator A. compensating windings B. interpoles C. both A and B 49. With dc generator which of the following regulation is preferred A. 1% regulation B. 50% regulation C. infinite regulation D. 100% regulation ANSWERS: 1. D 16.C 31.D 46.C 2. A 17.B 32.A 47.C 3. B 18.A 33.B 48.C 4. C 19.C 34.D 49.A 5. B 20.A 35.A 6. D 21.B 36.A 7. A 22.B 37.A 8. B 23.D 38.C 9. B 24.D 39.A 10. B 25.A 40.D 11. A 26.C 41.B 12. D 27.C 42.B 13. D 28.D 43.D 14. A 29.A 44.A 15. B 30.C 45.D 34 DC MOTORS 1. What is the effect produced by electric motors? A. magnetic effect only B. magnetic as well as heating effect C. heating effect only D. heating as well as chemical effect 2. The rotating part of a dc motors is known as A. pole C. armature B. stator D. carbon brush 3. The function of a commutator in a dc machine is A. to change alternating current to direct current B. to improve commutation C. for easy speed control D. to change alternating voltage to direct voltage 4. Carbon brushes are used in electric motor to A. brush off carbon deposits on the commutator B. provide a path for the flow of current C. prevent overheating on the armature windings D. prevent sparking during commutation 5. Voltage equation for dc motor is A. V = Eb+IaRa B. V = Eb - IaRa C. Eb = V+IaRa D. Eb = V x IaRa 6. Condition for maximum power output for a dc motor is A. Eb = V B. Eb = V/2 C. Eb = IaRa D. Eb = 0.5IaRa 7. The speed of dc motor is A. directly proportional to the back emf and inversely proportional to flux B. inversely proportional to back emf and directly proportional to flux C. directly proportional to emf as well as flux D. inversely proportional to emf as well as flux 35 8. The highest speed attained by a dc shunt motor is A. equal to infinity of rated flux B. higher than no load speed at rated flux C. equal to no load speed at rated flux D. lower than no load speed at rated flux 9. In a dc motor iron losses occur in A. yoke B. the armature C. the field D. brushes 10. The dummy coil in dc machines is used to A. eliminate reactance voltage B. eliminate armature reaction C. bring about mechanical balance of armature D. eliminate harmonic developed in the machine 11. An external resistance is added in series with the field of dc motor. When the motor runs, the effect of resistance is A. to reduce the speed of the motor B. to increase the speed of the motor C. to reduce the armature current drawn by the motor D. to reduce the losses 12. The speed of the dc shunt motor is required to be more than full load speed. This is possible by A. increasing the armature current B. decreasing the armature current C. increasing the excitation current D. reducing the field current 13. If a speed of a dc shunt motor increases, the back emf A. increases B. remains constant C. decreases and then increases D. decreases 14. The current flowing in the conductors of a dc motor is A. AC B. AC as well as DC C. DC D. transients 15. As the load is increased the speed of a dc shunt motor will A. remain constant B. increase proportionately C. increase slightly 36 D. reduce slightly 16. The current drawn by armature of a dc motor is A. V/ Ra C. (V – Eb) / Ra B. Eb / Ra D. (Eb – V) / Ra 17. If the current in the armature of dc series motor is reduced to 50% the torque of the motor will become A. 50% of the previous value B. 25% of the previous value C. 150% of the previous value D. 125% of the previous value 18. The shunt current flowing in a short shunt compound wound motor is given by A. Ish = B. Ish = C. Ish = V- D. none of these 19. In dc shunt motor, it the terminal voltage is reduced to half and torque remains the same, then A. speed will be half and armature current remain the same B. speed will be half but armature current remain the same C. speed will be half and armature current becomes double D. speed and armature current will remain the same 20. One dc motor drives another dc motor. The second dc motor when excited driven A. runs B. does not run as generator C. runs as a generator D. also run as motor 21. Armature torque of a dc motor is given by A. T = 0.159 ZIaP/A kg-m B. T = 0.162 / [2IcP/A] N-m C. T = 0.159 EbIa/N N-m D. none of these 22. A 4-pole lap wounded armature has 400 conductors and a flux per pole of 30 mWb. The emf generated, when running at 600 rpm, will be A. 240V C. 60V B. 120V D. 30V 23. The torque of a motor is A. the force N-m acting on the motor 37 B. the product of tangential force on the rotor and its radius C. the electrical power KW D. the power given to the load being driven to the motor 24. The armature current drawn by any dc motor is proportional to A. the voltage applied to the motor B. the torque required C. the flux required in the motor D. the speed of the motor 25. The output power of any electrical motor is taken from A. the armature B. the coupling mounted in the shaft C. the conductors D. the poles 26. The power stated on the name plate of any motor is always A. the output power of the shaft B. the power drawn in KVA C. the power drawn in KW D. the gross power 27. A starter is necessary to start a dc motor because A. it starts the motor B. it limits the speed of the motor C. it limits the back emf to a safe value D. it limits the starting current to safe value 28. The efficiency of any electrical machine / apparatus will be high, if A. its losses are minimum B. its losses are more C. voltage applied is constant D. the current drawn are minimum 29. The direction of rotation of a dc motor is reverse by A. reversing armature connection B. interchanging the armature and field connection C. adding resistance to the field circuit D. reversing supply connection 30. The armature of a dc motor is laminated A. to reduce the hysteresis losses B. to reduce the eddy current losses C. to reduce the inductivity of armature D. to reduce the mass of the armature 31. Which of the following is a correct statement about a series motor? A. its field winding consist of a thicker wire and less turns B. it can run easily without load 38 C. it has almost constant speed D. it has poor torque 32. Which of the following dc motor has the least drop in speed between no load and nominal load? A. shunt motor with commutating poles B. series motor without commutating poles C. compound motor without commutating poles D. series motor with commutating poles 33. The speed of a series motor at no load is A. zero C. 3600 rpm B. 3000 rpm D. infinity 34. The speed of a dc series motor decreases if the flux in the field winding A. remains constant B. increases C. decreases D. none of these 35. Which of the following motor is used to drive the constant speed line shafting lathes, blowers and fans? A. DC shunt motor B. DC series motor C. Cumulative compound motor D. Differential compound motor 36. If the back emf in a dc motor is absent, then A. motor run at a very high speed B. motor run at a very low speed C. motor will run at all D. motor will burn 37. The field flux of a dc motor can be controlled to achieve A. the speed lower than the rated speed B. the speed higher than the rated speed C. the speed at rated speed D. none of these 38. By providing a variable resistance across the series field (diverter) in the dc motor, speeds above normal can be obtain because A. armature current decreases B. flux is reduced C. line current decreases D. none of these 39. DC series motors are best suited for traction work because A. torque is proportional to the square of armature current and speed is inversely proportional to torque 39 B. torque is proportional to the square of armature current and speed is proportional to torque C. torque and speed are proportional to square of armature current D. none of the above 40. A series motor is started without load. The effect is that A. the torque increase rapidly B. the speed increase rapidly C. the current drawn increase rapidly D. the back emf decrease 41. The direction of rotation of a dc motor can be reversed by interchanging A. the supply terminal only B. the field terminal only C. the supply as well as field terminals D. none of these 42. The motor used for intermittent, high torque is A. dc shunt motor B. dc series motor C. differential compound motor D. cumulative compound motor 43. If the field of a dc shunt motor is opened A. it will continue to run at its rated speed B. the speed of the motor will become very high C. the motor will stop D. the speed of the motor will decrease 44. Which of the following is used for rolling mills? A. DC shunt motor B. DC cumulative compound motor C. DC series motor D. DC differential compound motor 45. Armature reaction is attributed to A. the effect of the magnetic field set-up by the armature current B. the effect of the magnetic field set-up by the field current C. copper loss in the armature D. the effect of the magnetic field set-up by the back emf 46. What will happen if the supply terminals of dc shunt motor are interchange? A. motor will stop B. motor will run at its normal speed in the same direction as it was running C. the direction of rotation is reverse D. motor will run at a speed lower than the normal speed in the same direction 47. When the electric train is moving down a hill the dc motor acts as A. dc series motor B. dc shunt motor 40 C. dc series generator D. dc shunt generator 48. Which of the following motors is suitable for high starting torque? A. shunt motor B. cumulative compound motor C. series motor D. compound motor 49. For which of the following dc motor is typical field of application mentioned? A. shunt motor : electric trains B. series motor : machine tools C. series motor : belt drive D. compound motor : wheel drive 50. Why is the air gap between the stator and armature of an electric motor keep as a small as possible? A. to get a stronger magnetic field B. to make the rotation easier C. to reach a higher speed of rotation D. to improve the air calculation 51. Interpoles are meant for A. increasing the speed of the motor B. decreasing the counter emf C. reducing sparking at the commutator D. converting armature current to 52. Which of the following method is most economical for finding the no-load losses of a large dc shunt motor is A. Hopkinson’s test B. Swinburne’s test C. retardation test D. none of these 53. The rated speed of a given dc motor is 1050 rpm. To turn the machine at 1200 rpm, which of the following control scheme will be used A. Armature current resistance control B. Field resistance control C. Ward-Leonard control D. none of these 54. It is preferable to start a dc series motor with some mechanical load on it because A. it will not turn at no load B. it will act as a starter to the motor C. it may developed excessive speed and damage itself D. none of these 41 55. If a flux of a dc motor approaches zero, its speed will approach A. infinity B. zero C. a stable value nearer to the rated speed D. none of these 56. As the load increase, the speed of shunt motor A. remains constant B. increase slightly C. reduces slightly D. none of these 57. A 230V dc series motor is connected to 230Vac. It will A. run slowly B. not run at all C. run with less efficiency D. none of these 58. The main function of a commutator in a dc motor is to A. prevent sparking B. convert ac to dc C. reduce friction D. convert dc to ac 59. Which of the following statement is incorrect? If a starter is not used with large dc motor, it will draw a starting current which A. is many times its full load current B. will produce excessive line voltage drop C. will damage the commutator D. will produce very low starting torque ANSWERS: 1. B 16.C 31. A 46.B 2. C 17.B 32. A 47.C 3. D 18.B 33. D 48.C 4. B 19.C 34.B 49.D 5. A 20.C 35.A 50.A 6. B 21.C 36.D 51.C 7. A 22.B 37.B 52.B 8. C 23.B 38.B 53.B 9. A 24.B 39.A 54.C 10. C 25.B 40.B 55.A 11. B 26.A 41.B 56.C 12. D 27.D 42.D 57.C 13. A 28.A 43.B 58.B 14. A 29.A 44.B 59.D 15. D 30.B 45.A 42 AC FUNDAMENTALS 1. When using circuit laws and rules must use A. maximum value B. effective value C. average value D. peak to peak value 2. A 60 Hz frequency would cause an electric light to A. turn on and off 120 times per second B. flicker noticeable C. turn on and off 180 times per second D. turn on and off 60 times per second 3. The relationship between frequency f, number of revolution per second n and pair of pole is given by A. f = n/p C. f = np B. f = n/2p D. f = 2np 4. The difference between the peak +ve plus value and the peak –ve value of an ac voltage is called the A. maximum value B. average value 43 C. effective value D. peak to peak value 5. The greatest value attained during one half of the cycle is called the A. peak value B. average value C. r.m.s. value D. effective value 6. The root mean square (r.m.s) value of ac is the same as A. instantaneous value B. effective value C. average value D. maximum value 7. The r.m.s. value of sine wave is equal to A. 0.637 max. value B. 0.707 max. value C. 0.506 max. value D. 1.414 max. value 8. Form factor is defined as A. r.m.s. value / peak value B. max. value / r.m.s. value C. r.m.s. value / average value D. effective value / r.m.s. value 9. The value of form factor for a pure sine wave is A. 1.414 C. 0.637 B. 0.707 D. 1.11 10. The value of peak factor for a pure sine wave is A. 1.414 C. 0.637 B. 0.707 D. 1.11 11. If the current and voltage are out of phase by 90 degrees, the power is A. 1.1 VI C. minimum B. maximum D. zero 12. if e1 = A sin t and e2 = B sin ( t - ) then A. e1 lags e2 by ° B. e2 lags e1 by ° C. e2 leads e1 by ° D. e1 leads e2 by ° 13. The equation for 25 cycles current sine wave having rms value 30 amperes, will be A. 30 sin 25t 44 B. 30 sin 50t C. 42.4 sin 25 t D. 42.4 sin 50π t 14. The voltage v = 90 cos(wt – 161.5) may be represented as sine function by A. 90 sin (wt + 18.5) B. 90 sin (wt – 71.5) C. 90 sin (wt + 71.5) D. 90 sin (wt – 18.5) 15. Which of the following frequencies has the longest period? A. 1 Hz C. 1 KHz B. 10 Hz D. 100KHz 16. RMS value and the mean value is the same in the case of A. square wave B. sine wave C. triangular wave D. half wave rectified sine wave 17. If emf in a circuit is given by e = 100 sin 628t the maximum value of voltage and frequency are A. 100V, 50Hz B. 100V, 100Hz C. 50 V, 50Hz D. 50 V, 100Hz 18. When the sole purpose of an alternating current is to produced heat, the selection of conductor is based on A. average value of current B. peak value of current C. rms value of current D. any of these 19. The form factor of dc supply voltage is always A. infinite C. 0.5 B. zero D. unity 20. The frequency of sinusoidal signal with a period of 2ms is A. 500Hz C. 1 KHz B. 250Hz D. 500KHz 21. The period of the voltage 2 cos 4500 t + 7 sin 7500 t is A. 2.5s C. 2.51ms ANSWERS: 1. BB. 2.51ns 11.D D. 2.51μs 21.C 2. A 12.B 3. C 13.D 4. D 14.B 5. A 15.A 6. B 16.A 45 7. B 17.B 8. C 18.C 9. D 19.A 10. A 20.A AC CIRCUITS 1. The total voltage in a series RL circuit ___ the current by an angle ____ A. lags, of 900 B. lags, between 0 to 900 C. leads, between 0 to 900 D. leads, between 90 to 1800 2. In a series RL circuit, the inductor current ____ the resistor current A. lags C. is equal B. leads D. is negative 3. The impedance triangle is similar to the ____ triangle with the resistance phasor in place of the _____ A. current, resistor current B. current, resistor voltage 46 C. voltage, impedance D. voltage, resistor voltage 4. In the impedance triangle the inductive reactance and impedance phasor are analogous to the ____ and ____ phasor respectively in the voltage triangle A. inductive voltage, total voltage B. inductive current, total current C. inductive voltage, resistive voltage D. inductive current, resistive current 5. In a series RL circuit phasor diagram, total voltage may be represented by the ____ phasor and resistor voltage may be represented the ____ phasor A. current, voltage B. current resistance, current C. impedance, resistance D. impedance, inductance 6. The phase angle of a series RL circuit is the angle between the ____ phasor and the ____ phasor A. resistance, inductive reactance B. resistance, impedance C. inductive reactance, impedance D. none of these 7. The phase angle of series RL circuit may be computed ___ as ____ or ___ or A. cos-1 R/XL, sin-1XL/R, tan-1R/Z B. cos-1 R/Z, sin-1XL/R, tan-1R/XL C. cos-1 Z/XL, sin-1 R/Z, tan-1 XL/R D. cos-1 R/Z, sin-1XL/Z, tan-1 XL/R 8. A 5 ohms resistor and an inductor of 0.025 Henry connected in series with an effective voltage supply of 10V 200 rad/sec, the effective value of the resistor voltage is ____ volts A. 5 C. 5/ B. 5 D. 10 9. A(n) _____ stores and return energy to a circuit when a (n) ____ dissipate energy. A. resistor, impedance B. resistor, inductor C. inductor, resistor D. inductor, reactance 10. For an RL circuit, the power factor cannot be less than ____ or greater than ____ A. 0, 1 C. 0, -1 B. 1, 0 D. -1, 0 11. The voltage across the capacitor ___ the current through it by ____ 47 A. lags, 450 C. leads, 00 B. lags, 900 D. leads, 900 12. If the resistance in a series RC circuit is increase in magnitude of the phase angle A. increases B. remain the same C. decreases D. changes in an undetermined manner 13. In a series RC circuit, the current _____ the total voltage by an angle _____ A. lags, of 450 B. lags, of zero C. leads, between 00 to 900 D. leads, of 900 14. The resistance phasor of a series RC circuit points to the right. The capacitive reactance phasor points ____ while the diagonal of the rectangle having there two phasors as sides represents the ____ A. up, impedance B. down , impedance C. left, current D. up, total voltage 15. The phase angle for a series RC circuit is defined as the angle between the ___ and the ___ phasors A. current, resistance voltage B. current, total voltage C. resistance voltage, capacitor voltage D. R, Xc 16. The phase angle for a series RC circuit may be computed as the angle between the ___ and ___ phasors A. resistance, impedance B. resistance, reactance C. reactance, impedance D. none of these 17. If series RC circuit with R = 10 ohms and Xc = 10 ohms carries current of 1 ampere effective value the resistor voltage is ___ volts effective and the capacitor voltage is ___ volts effective A. 10 , 10/ B. 10, 10 C. 10 , 10 D. 5, 10 18. The power dissipated in a series RC circuit with R = 10 ohms and Xc = 10 ohms carrying an effective current of 3 ampere is ____ watts 48 A. 30 C. 90 B. 30/2 D. 90/2 19. The magnitude of the power factor of an RC circuit with R = 10 ohms, Xc = 10 ohms , I= 2 amp effective is A. 1 C. 0.707 B. 0.5 D. 0 20. The power dissipated in an RC circuit with R = 30 ohms, Xc = 40 ohms and E = 100V effective A. 60 C. 100 B. 80 D. 120 21. The net reactance in an RCL circuit is A. XL C. XC + XL B. XC D. XL – XC 22. The impedance of a series RLC circuit is A. B. C. D. 23. There will ____ be a frequency, called the ____ frequency, at which ___ A. sometimes, natural. XL = XC B. always, natural. R = 0 C. always, resonant, XL = XC D. sometimes, resonant, R = 0 24. The formula of resonant frequency is f= _______. A. C. 2 B. D. 25. For the series RLC circuit at resonance the current amplitude is ____ for a fixed voltage amplitude and power factor is ______. A. minimum, zero B. minimum, unity C. maximum, zero D. maximum, unity 26. In an RLC circuits, the impedance at resonance is A. maximum C. infinity B. minimum D. zero 49 27. The current in RLC circuit at resonance A. maximum C. infinity B. minimum D. zero 28. In RLC circuit, the current at resonance is A. minimum in parallel circuit and maximum in series circuit B. maximum in parallel circuit and minimum in series circuit C. maximum in both the circuit D. minimum in both the circuit 29. A series resonant is capacitive at f = 100Hz. The circuit will be inductive somewhere at A. f < 100 Hz B. f > 100 Hz C. f = 100 Hz by increasing the value of the resistance D. none of these 30. At frequency less than the resonant frequency A. series circuit is capacitive and parallel circuit is inductive B. series circuit is inductive and parallel circuit is capacitive C. both circuit are inductive D. both circuit are capacitive 31. In series as well as in parallel resonant circuit, increasing the value of resistance would lead to A. increase in the band-width of both the circuit B. decrease in the band-width of both the circuit C. increase in band-width in series circuit and decrease in parallel circuit D. decrease in band-width in series circuit and increase in parallel circuit 32. The value of current of resonance in a series RLC circuit affected by the value of A. R C. L B. C D. all of these 33. In resonant circuit, the power factor at resonant is A. zero C. 0.5 B. 1 D. 0.707 34. Which of the following statement is true for a series RLC circuit tuned at resonant frequency A. the voltage across C > applied voltage B. the voltage across L > applied voltage C. the voltage across L and C > applied voltage D. the voltage across both L and C < applied voltage 35. The reactance curve for the circuit shown at anti-resonance is shown by 50 A. B. C. D. 36. At anti-resonance for the above circuit, the frequency is given by A. B. C. D. 37. The frequency at which maximum voltage occurs across the inductance in RLC series circuit is A. B. C. D. 38. The frequency at which maximum voltage across the capacitance in RLC series circuit is given by 51 A. B. C. D. 39. If f1 and f2 are half power frequencies and to be resonance frequency, the selectivity of RLC series circuit is given by A. B. C. D. 40. In a series of RC circuit, the voltage across the capacitor and the resistor are 60V and 80V respectively. The input voltage should be A. 70  45°V C. 105  42°V B. 100 37°V D. 108 60°V 41. To a series RLC circuit, a voltage of 10V is applied. if Q of the coil at resonant frequency is 20, the voltage across the inductor at resonant frequency will be A. 200V C. 75V B. 100V D. 50V 42. The current flowing in L and C at parallel resonant are A. zero C. infinite B. equal D. different 43. The exact natural frequency of free oscillations in an oscillatory circuit with the capacitance of 0.055μf, inductance 2μH and resistance 1 ohm will be A. 478 kHz C. 272 kHz B. 337 kHz D. 192 kHz 52 44. A coil with a large distributed capacitance has a A. low resistance B. low Q C. low resonant frequency D. high resonant frequency 45. The transient current are due to A. voltage applied to circuit B. resistance of the circuit C. impedance of the circuit D. changes in the stored energy in the inductance and capacitance 46. To a highly inductive circuit, a small capacitance is added in series. The angle between voltage and current will A. increase B. decrease C. remain nearly the same D. become undetermined ANSWERS: 1. C 16.A 31. D 46.B 2. A 17.B 32. D 3. D 18.C 33. B 4. A 19.C 34.C 5. C 20.D 35.B 6. B 21.D 36.A 7. D 22.D 37.C 8. A 23.C 38.B 9. C 24.D 39.C 10. A 25.D 40. B 11. B 26.B 41.A 12. C 27.A 42.B 13. C 28.A 43.A 14. B 29.B 44.D 15. B 30.A 45.D THREE PHASE SYSTEM 1. In a balanced three phase star connected circuit, the line voltage are equal A. to the line current B. to the phase voltage C. and so are the line currents D. but the line currents are unequal 2. The type of ac distribution system commonly used to supply both light and power is the A. open delta system B. three phase delta system 53 C. three phase star system with neutral wire D. three phase star system without neutral line 3. The phase displacement between phasors in polyphase system is always A. 90 degrees B. 120 degrees C. 360 degrees divide by the number of phases D. 60 degrees 4. In a balanced three phase star connected system, the line voltage is A. the phasor difference of two phase voltages B. the phasor sum of two phases voltages C. 0.707 times phase voltage D. 1.414 times phase voltage 5. In a star connected system, the line current is A. 0.707 times the phase current B. 1.732 times the phase current C. equal to the phase current D. 1.414 times the phase current 6. The advantages of star connection for the same phase voltage is that it gives A. step down current B. extra step up voltage C. extra step up current D. extra step up power 7. Power in a three phase star system is equal to A. 3 x VL x IL x power factor B. 3 xVL x Iph x power factor C. 1.732x Vph x Iph x power factor D. 3 x Vph x Iph x power factor 8. Power in a three phase delta system with balanced load is equal to A. 1.732 xVL X |Lx power factor B. 1.732 x Vph x |ph x power factor C. 3 x Vph x |L x power factor D. 3 x VL X |L x power factor 9. In delta connected system, the line current is A. 1.414 times phase current B. phasor sum of the two phase current C. equal to the phase current D. 1.732 times the phase current 10. Power in star connected system is A. equal to that delta system B. 1.414 times the delta system C. 1.732 times the delta system 54 D. 3 times the delta system 11. For an unbalance load, which connection is suitable A. 3 – wire open delta B. 4 – wire star connection C. 3 – wire delta connection D. 3 – wire star connection 12. What is the minimum number of wattmeter required for measuring power of a three phase balance load A. two B. four C. one D. three 13. The power is to be measured for a balanced delta connected load whose terminals cannot be opened. How many wattmeter do you need A. Four C. two B. one D. three 14. What is the minimum number of wattmeter required to measure unbalanced power of a three phase system A. Two C. three B. four D. one 15. In two wattmeter method, the reading of the wattmeter will be identical when A. load in one of the phases is zero B. power factor is unity C. power factor is 0.5 D. neutral is earthed 16. Two wattmeter can be used to measure 3-phase power for a A. balanced and unbalanced load B. unbalanced load only C. balanced load only D. unity power factor only 17. In 2-wattmeter method, the reading in one of the wattmeter is zero when A. power factor is unity B. power factor is 0.5 C. load in one of the phases is zero D. a neutral wire is not provided 18. For a three phase unbalance load A. the power factor of each phase is proportional to the load B. the power factor of each phase will be the same C. the power factor of at least one of the phases must be leading D. the power factor of each phase may be different 55 19. A wattmeter is installed in a balanced 3-phase system with current coil at line A while voltage coil across B and C. The wattmeter will measure A. total power B. real power ANSWERS: C. active power 1. C 11.B D. reactive power 2. C 12.C 3. C 13.C 4. A 14.A 5. C 15.B 6. B 16.A 7. D 17.B 8. A 18.D 9. B 19.D 10. A POWER FACTOR 1. In a pure reactive circuit, the power factor is A. lagging C. leading B. zero D. reactive power 2. Power factor is defined as the ratio of A. volt ampere in watts B. watts to volt-ampere C. Volt ampere reactive to watts D. watts to volt ampere reactive 3. In a series circuit consisting of resistance and reactance, power factor is defined as the ratio of A. resistance to impedance B. resistance to reactance C. reactance to impedance 4. For a parallel circuit consisting of resistance and reactance the value of power factor is the ratio of A. impedance to reactance B. reactance to impedance C. resistance to impedance D. impedance to resistance 5. It is not easy to find the value of impedance in parallel circuit but power factor can be easily obtained as the ratio of A. active current to line current B. reactive current to line current C. line current to active current 6. The power factor is ac circuit containing both a resistor and a capacitor is 56 A. more than unity B. leading by 90 degrees C. between 0-1 leading 7. In an ac circuit, a low value of reactive volt ampere compared with watts indicates A. high power factor B. unity power factor C. leading power factor 8. In a given ac circuit when power factor is unity the reactive power is A. maximum B. equal to R C. zero 9. The capacitor of power factor correction are rated in terms of A. voltage B. VA C. kW D. kVAR 10. Poor power factor results in all of the following except A. overloading of transformers B. overloading of alternators C. reduction in power losses D. reduction in load handling capacity of electrical system 11. Power factor of an inductive circuit can be improved by connecting to it in A. series B. parallel C. either series or parallel D. depends on the value of the capacitor 12. For the same load, if the power factor of load is reduced, it will A. draws more current B. less current C. same current but power D. less current but more power 13. The power factor if a incandescent bulb is A. 0.8 lagging B. 0.8 leading C. unity D. zero 14. Power factor of magnetizing component of a transformer is A. unity B. 0.8 lagging C. always leading 57 D. zero 15. One of the reasons for improving the power factor is A. to increase the reactive power B. to decrease the reactive power C. to increase the real power 16. Another reason for improving the power factor is A. to avoid poor voltage regulation B. to keep voltage regulation constant C. to increase the voltage regulation 17. Power factor improvement may be achieved by the use of A. synchronous motor B. inductor motor C. long transmission lines 18. The advantage of using static capacitor to improve the power factor is because they A. are not variable B. are almost loss free C. provide continuous change of factor 19. Many industrial tariffs penalize consumers whose power factor falls A. below 0.85 B. below unity C. between 0.85 and 0.95 20. A resistor of 40 ohms and inductive reactor of 30 ohms are joined in parallel across 120 volts supply. What is the power factor of the circuit? A. 0.6 C. 10.725 B. 0.8 D. zero 21. A factory takes a load of 1000 KW and has a reactive power of 1000 KVAR. Its power factor is A. 0.6 C. 0.8 B. unity D. 0.7 22. A current of 10 amperes at a power factor of 0.8 lagging is taken from 250V ac supply. The reactive power of the system is A. 2000 watts C. 1500 watts B. 2000 VA D. 1500 VAr ANSWERS: 1. B 11.B 21.D 2. B 12.A 22.D 3. A 13.C 4. D 14.D 5. A 15.B 6. C 16.A 58 7. A 17.A 8. C 18.B 9. D 19.A 10. C 20.A NETWORK THEOREMS 1. Kirchoff’s law is applicable to A. AC circuits only B. passive network only C. AC as well as DC circuits D. DC circuits only 2. An ideal current source has zero A. voltage on no load B. internal resistance C. internal conductance 3. A close path made of several branches of the network is known as A. loop C. branch B. junction 4. An ideal voltage source is that which A. has terminal voltage in proportion to current B. has zero internal resistance C. has terminal voltage proportion to the load 5. A passive network has A. no source of emf B. no source of current C. neither source of current nor of emf 59 6. Which of the following is an active element of a circuit A. ideal current source B. resistance C. inductance D. capacitance 7. The relationship between voltage and current is the same for the opposite directions of current in case of A. bilateral network B. active network C. unilateral D. passive network 8. Which of the following statement is not correct? A. voltage source is an active source B. current source is a passive source C. resistance is a passive element D. conductance is a passive element 9. A network is said to be non-linear if it does not satisfy A. homogeneity condition B. superposition condition C. both A and B D. associative condition 10. Which of the following statement is incorrect? A. ideal voltage source is one whose internal conductance is zero B. ideal current source is one whose internal conductance is zero C. ideal voltage source is one whose internal resistance is zero D. ideal voltage source is one whose generated voltage is equal to available terminal voltage 11. Which of the following is not a non-linear element? A. diode B. transistor C. heater coil D. electric arc with unlike electrode 12. Which of the following theorems enables a number voltage (or current) source to be combined directly into a single voltage (or current) source? A. Compensation theorem B. Reciprocity theorem C. Superposition theorem D. Millman’s theorem 13. Thevenin’s theorem is applicable to network of A. a.c. circuit only 60 B. d.c. circuit only C. a.c. and d.c. circuit both D. none of these 14. For open circuited condition of Thevenin’s theorem all sources of emf in the network are replaced by A. their internal impedance B. their internal resistance C. as total a big source of emf 15. The current in any branch of a network in case of Thevenin’s theorem is the same if it were connected to a generator of A. different rating B. emf E1 and internal impedance Z1 C. low rating D. emf E1 with internal impedance zero 16. In order to find Z the Thevenin’s theorem A. all independent voltage and current sources are short circuited B. all independent voltages sources are short circuited and all independent current sources are open circuited C. all independent current sources are short circuited and independent voltage source are open circuited D. all independent voltage sources are open circuited and all independent current sources are open circuited 17. Regarding Thevenin’s equivalent, which of the following is not correct? A. The voltage source in the Thevenin equivalent circuit is open circuit voltage of the network when load is disconnected B. The Thevenin equivalent resistance is the resistance of the network when all voltage sources are short circuited C. The Thevenin equivalent resistance is calculated when all voltage sources are open circuited D. Thevenin equivalent is the voltage equivalent of the network 18. Regarding Norton’s equivalent, which of the following is not correct? A. Norton’s equivalent is the voltage equivalent of the network B. Norton’s equivalent is the current equivalent of the network C. Norton’s equivalent resistance is the same as the Thevenin’s equivalent resistance D. The load is connected in parallel to the Norton equivalent resistance and Norton’s equivalent source 19. Reciprocity theorem is valid for A. active network only B. passive network only C. active and passive network both D. none of these 20. For reciprocity theorem to be applicable to a network in which 61 A. generators are present B. capacitor is present C. inductor is present D. generators are not present 21. In compensation theorem a network containing generator can be replaced by A. its zero internal impedance B. its infinite impedance C. another generator D. L. C. circuit 22. The most important feature of superposition theorem application is A. that the process is ease very much B. to find dc level in a network that has both sources C. that number of equations needed to be solved is reduced very much D. none of the above 23. Open circuit voltage is the p.d. between two points when the impedance between these points is A. infinity C. zero B. reactive D. capacitive 24. Norton’s theorem reduces a two terminal network to A. a constant voltage source and an impedance in parallel B. a constant voltage source and an impedance in series C. a constant current source and an impedance in parallel D. a constant current source and an impedance in series 25. For the same original network end load, Thevenin’s and Norton’s equivalent circuits are related by A. = = B. = / C. = = D. = 26. If an electrical network having one or more than one voltage source, is transformed into equivalent electrical network with a single voltage source (which is short circuit current of previous circuit) with parallel internal resistance of the network with all current source replaced by their internal resistance. The above illustration is called A. Thevenin’s theorem B. reciprocity theorem C. Norton’s theorem D. Superposition theorem 27. The superposition theorem requires as many circuit to be solve as there are A. meshes 62 B. nodes C. sources D. all of the above 28. For maximum power transfer, according to maximum power transfer theorem, source impedance A. must be very large as compared to the load impedance B. must be complex conjugate of load impedance C. must be equal to the load impedance D. must be very small as compared to the load impedance 29. In the case of delta connected circuit, when one resistor open, power will be A. unaltered B. reduced by 1/3 C. reduced to 1/9 D. reduced to 1/6 30. A source V has an internal impedance = (R + jX) when it is connected = R – jX the power transferred is A. /4 C. /R B. / 4R D. / 2R 31. The superposition theorem is applicable to A. linear response only B. linear and non-linear response only C. linear, non-linear and time variant response ANSWERS: 1. C 16.B 31. A 2. C 17.C 3. A 18.A 4. B 19.B 5. C 20.D 6. A 21.A 7. A 22.B 8. B 23.A 9. C 24.C 10. A 25.A 11. C 26.C 12. D 27.C 13. C 28.B 14. A 29.B 15. B 30.B 63 TRANSFORMERS 1. The principle of working of a transformer is A. static induction B. dynamic induction C. mutual induction D. self induction 2. Transformer is used to change the value of A. frequency C. power B. voltage D. power factor 3. The path of magnetic flux in the transformer of A. low reactance B. high reactance C. high conductivity D. low resistance 4. Electric power is transformed from one coil to the other coil in a transformer A. physically B. magnetically C. electrically D. electromagnetically 5. A transformer operates A. always at unity power factor B. has its own power factor C. at power factor below a particular value D. at power factor depending on the power factor load 6. The laminations are made from A. low carbon steel B. silicon sheet steel C. nickel alloy steel stampin

Current Electricity Objective Questions PDF

Document Details

Tags

Related

Summary

Full Transcript