IRCON Technical Interview Questions

1:- What are the various kind of cables used for transmission? Cables, which are used for transmitting power, can be categorized in three forms: ? Low-tension cables, which can transmit voltage upto 1000 volts. ? High-tension cables can transmit voltage upto 23000 volts. ? Super tension cables can transmit voltage 66 kV to 132 kV. 2:- Why back emf used for a dc motor? highlight its significance. The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux, opposes the current flowing through the conductor, when the armature rotates, is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero. 3:- What is slip in an induction motor? Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ?S?. Explain the application of storage batteries. Storage batteries are used for various purposes, some of the applications are mentioned below: ? For the operation of protective devices and for emergency lighting at generating stations and substations. ? For starting, ignition and lighting of automobiles, aircrafts etc. ? For lighting on steam and diesel railways trains. ? As a supply power source in telephone exchange, laboratories and broad casting stations. ? For emergency lighting at hospitals, banks, rural areas where electricity supplies are not possible. 4:- What are the advantages of P-N diode or PIN diode ? Ans:-Decrease in capacitance because capacitance is inversely proportional to the separation of P and N regions, So it allows a diode a faster response time. Hence ,PIN or P-N diodes are used at higher frequencies Approximately 300 MHz or more then 300 MHz. Another advantage is that, the possibility of greater electric field between P and N junctions. It enhances the electron-hole pair generation there by enabling PIN diode to process even for very weak input signals 5:- How can you convert AC input signal into DC output signal using power supply and which components are used in this procedure ? Ans:- AC input signal can be converted in to DC output signal by using REGULATED power supply and the components used for the procedure are transformer,rectifier,filter,Voltage regulator and voltage dividor 6:- What is purpose of Transformer in Electrical engineering ? Ans:- The job of transformer in electrical engineering is either step up or step down. Mostly step down transformers are used in electrical engineering. The job of transformer is to suit the requirement of the solid state electronic devices and circuits fed by the dc power supply. It also provide isolation from the supply line which is an important safety consideration. 7:- Why we use underground cables ? Ans:- underground cables are used where over-head lines are not possible as in large cities despite the fact that in their cost, cost per kW (kilo watt) per kilo meter is much more as compared to over head transmission lines. Another advantage of over-head system for distributors is that tapping can be made at any time with out having any disturbance which is very important for rapidly developing areas. 8:-How can you divide cables into group ? Ans:- cables are divided in to three groups 1: Low tension cables ? up to 1000 volts 2: High tension cables ? up to 23000 volts 3: Super tension cables ? from 66 kV to 132 kV 9:- What are the essential parts of the Generators ? Ans:- The generator consist of the following essential parts: Magnetic Frame or Yoke, Pole shoes ,Pole coils or field coils , Armature core, Armature winding or conductors,commutator and brushes and bearings 10:- What is the purpose of armature core ? Ans:- It houses the armature conductors or coils and causes them to rotate and hence cut the magnetic flux of the field magnets. In addition to this its the most important function is to provide a path of very low reluctance to the flux through the armature from a N ? Pole to a S ? Pole.(It is cylinderical in shape and is built up of usually circular sheet steel discs or laminations approximately 0.55 mm thick) 11:- What are the purpose of Yokes ? Ans:- It provide mechanical support for the poles and acts as a protecting cover for the whole machine and it carries the magnetic flux produced by the poles. 12:- Is that true, that the use of dc motors are either essential or else is advantageous to a degree sufficient to make it preferable to alternating current? Ans:- Few cases are listed below : 1: Because of their excellent starting and over load characteristic dc motors are most suitable for electric traction on tramways, sub urban and under ground railways. 2: DC is absolutely essential for electrolytic and electro-chemical processes such as electro platting, electro ? refining , production of aluminium , Cu and other metals by electro-lysis and fertilizers 3: It is essential for battery charging work. 4: It is necessary for running arc lamps for cinema projectors and search lights and also for some types of arc- welding. 5 : The most important aspect of this is that,DC motors are more superior to a.c motors for duties where frequent starting angainst heavy torque ,close speed adjustment and frequent reversals are required for example elevators , printing process , large machine tools drivers and certain steel mill equipments 13 :- Inside a conducting sphere which thing is always remains constant ? Ans:- Potential should be remain constant inside a conducting sphere 14:- Like a resonant R ? L ? C circuits what should parallel resonant circuit also had ? Ans:- Like a resonant RLC circuits parallel resonant circuit should also had a power factor of unity 15:- What is thyristor? Ans:- The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as a switch conducting when their gate receives a current pulse and continue to conduct for as long as they are forward biased. Thyristors are mainly used where high currents and voltages are involved and are often used to control alternating currents where the change of polarity of the current causes the device to automatically switch off; Thyristors can also be found in power supplies for digital circuits where they can be used as a sort of circuit breaker 16:- What is the power ratio between power in Star and Delta circuit? Ans:- power is same,its only the line currents and voltages which differ in star and delta circuits and you can say that it is 1:1 17:- What is a Transducer? Ans:- Transducer is a device which converts physical quantity into electrical quantity. As-Thermocouple (convert temperature into electrical volt or current) 18:- What is UPS ? Ans:- UPS mean uninterruptible power supply.This system can be of two major types and work to ensure uninterruptible power within a specified period before backup comes in. There is a static type and the mechanical type. The static type is common and consists of the rectifier/battery/inverter making up the system where as the mechanical type consists of transfer switch backup generator and an electric motor directly coupled to motor-generator through a flywheel. Static type has the advantage of less maintenance when compared with the mechanical type with rotating parts. 19:- For an 100kw generator, only 50kw of load is connected. will the generator generate only 50kw or 100kw? Ans :- If we have 100KW generator and load is 50Kw generator generate only 50kw.but If we have 100KW generator and connected more then 100KW the generator tripped at overload (if there is circuit breaker). 20:- Why star delta starter is preferred with induction motor? Star delta starter is preferred with induction motor due to following reasons: ? Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses. ? Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused. ? In addition, starting torque is increased and it prevents the damage of motor winding. State the difference between generator and alternator Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used. 21:- Why AC systems are preferred over DC systems? Due to following reasons, AC systems are preferred over DC systems: a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution. b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission c. From power stations, AC is produced so it is better to use AC then DC instead of converting it. d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt. 22:- How can you relate power engineering with electrical engineering? Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of energy in electrical form. Design of all power equipments also comes under power engineering. Power engineers may work on the design and maintenance of the power grid i.e. called on grid systems and they might work on off grid systems that are not connected to the system. What are the uses of PLL circuits? What is voltage build up of a generator? Differentiate between MC and MI instruments? Are Single induction motor self starting? How is the alternator synchronized to the main busstar? what is arc formation? What is the basic circuitry for voltage stabilizer? what do the three pin of a socket represents? what is regenerative breaking? Give an example where a transformer is used in a DC application? Ircon civil engineering question papers Ircon civil engineering questions 1. This question consists of 27 (Twenty Seven) multiple-choice type sub-questions each carrying one mark. The answers to the multiple choice questions MUST be written only in the boxes corresponding to the question number by writing A, B, C or D in the answer book. (27 x 1 = 27) 1.1. If A, B, C are square matrices of the same order, (ABC) -l is equal to C -l A -1 B -1 C -l B -1 A -1 A -1 B -1 C -l A -1 C -l B -1 1.4. Consider the following two statements: 2. The maximum number of linearly independent column vectors of a matrix A is called the rank of A. II. If A is an n x n square matrix, it will be nonsingular if rank A = n. With reference to the above statements, which of the following applies? (a) Both the statements are false. (b) Both the statements are true. (c) I is true but II is false. (d) I is false but II is true. 3 The dimensions for the flexural rigidity of a beam element in mass (M), length (L) and time (T) is given by (a)MT -2 (b) ML 3T -2 (c) ML -lT -2 (d) ML -l T 2­ 4 A two span beam with an internal hinge is shown below. 5 Pick the incorrect statement from the following four statements: On the plane which carries maximum normal stress, the shear stress is zero. Principal planes are mutually orthogonal. On the plane which carries maximum shear stress, the normal stress is zero. The principal stress axes and principal strain axes coincide for an isotropic material. 6 . A frame ABCD is supported by a roller at A and is on a hinge at C as shown below: The reaction at the roller end A is given by (a) P (b) 2 P (c) P/2 (d) Zero. 7 The following two statements are made with reference to a simply supported under-reinforced RCC beam: I. Failure takes place by crushing of concrete before the steel has yielded. II. The neutral axis moves up as the load is increased. With reference to the above statements, which of the following applies? Both the statements are false. I is true but II is false. Both the statements are true. I is false but II is true. 8. The stress-strain diagram for two materials A and B is shown below: The following statements are made based on this diagram: (I) Material A is more brittle than material B. (II) The ultimate strength of material B is more than that of A. With reference to the above statements, which of the following applies? Both the statements are false. (b) Both the statements are true. (c) I is true but II is false. (d) I is false but II is true. 9. Four column of the same material and having identical geometric properties are supported in different ways as shown below: It is required to order these four beams in the increasing order of their respective first buckling loads. The correct order is given by (a) I, II, III, IV (b) III, IV, I, II (c) II, I, IV, III (d) I, II, IV, III 12. A soil sample has a void ratio of 0.5 and its porosity will be close to 50% 66% 100% 33% 13. A borrow pit soil has a dry density of 17 kN/m 3. How many cubic meters of this soil will be required to construct an embankment of 100 m 3 volume with a dry density of 16 kN/m 3. (a) 94 m 3 (b) 106 m 3 (c) 100 m 3 (d) 90 m 3 14. The group efficiency of a pile group (a) will be always less than 100%. (b) will be always greater than 100% (c) may be less than 100% or more than 100%. (d) will be more than 100% for pile groups in cohesion less soils and less than 100% for those in cohesive soils. 15. The two criteria for the determination of allowable bearing capacity of a foundation are (a) tensile failure and compression failure. (b) tensile failure and settlement. (c) bond failure and shear failure. (d) shear failure and settlement. 16. If duty (D) is 1428 hectares/cumec and base period (B) is 120 days for an irrigated crop, then delta ( D ) in meters is given by (a) 102.8 (b) 0.73 (c) 1.38 (d) 0.01 17. The relation that must hold for the flow to be irrotational is 18. Cavitation is caused by (a) high velocity (b) low pressure (c) high pressure (d) high temperature 19. If the pump head is 15m, discharge is 0.464 m 3/s and the motor speed is 1440 rpm at rated condition, the specific-speed of the pump is about (a) 4 (b) 26 (c) 38 (d) 1440 20. The BOD removal efficiency, in percentage, during primary treatment, under normal conditions is about (a) 65% (b) 85% (c) 30% (d) Zero 21. Critical factors for the activated sludge treatment process are (a) maximum hourly flow rate. (b) maximum and minimum flow rate. (c) maximum hourly flow rate and maximum daily organic load. (d) minimum hourly flow rate and minimum daily organic load. 22. Use of coagulants such as alum (a) results in reduction of pH of the treated water. (b) results in increase of pH of the treated water. (c) results in no change in pH of the treated water. (d) may cause an increase or decrease of pH of the treated water. 23. The disinfection efficiency of chlorine in water treatment (a) is not dependent on pH value. (b) is increase by increased pH value. (c) remains constant at all pH values. (d) is reduced by increased pH value. 24. The standard plate size in a plate bearing test for finding modulus of subgrade reaction (k) value is 100 cm diameter 50 cm diameter 75 cm diameter 25 cm diameter 25. Width of carriageway for a single lane is recommended to be (a) 7.5 m (b) 7.0 m (c) 3.75 m (d) 5.5 m 26. Stopping sight distance is the minimum distance available on a highway which is the (a) distance of sufficient length to stop the vehicle without collision. (b) distance visible to a driver during night driving. (c) height of the object above the road surface. (d) distance equal to the height of the driver's eye above the road surface. 27. Bituminous materials are commonly use in highway construction because of their good (a) tensile and compression properties. (b) binding and water proofing properties. (c) shear strength and tensile properties. (d) bond and tensile properties. 28. This question consists of24 (Twenty Four) multiple-choice type sub-questions, each carrying TWO marks. The answers to the multiple choice questions MUST be written only in the boxes corresponding to the question numbers writing A, B, C or D in the answer book. (24 x 2 = 48) 2.9. The limit of the function f(x) = [1- a 4 / x 4] as x ® ¥ is given by 1 exp[- a 4 ] ¥ Zero 2.5. The maxima and minima of the function f(x) = 2x 3 - 15x 2 + 36x + 10 occur, respectively, at (a) X = 3 and X = 2 (b) X = 1 and X = 3 (c) X = 2 and X = 3 (d) X = 3 and X = 4 30. The four cross sections shown below are required to be ordered in the increasing order of their respective shape factors. Which of the following order is correct? (a) III, I, IV, II (b) I, II, III, IV (c) III, IV, I II (d) III, IV, II, I 31. A simply supported beam with an- overhang is traversed by a unit concentrated moment from the left t>a. the right as shown below: Figure 32The following two statements are made with reference to the planar truss shown Figure I. The truss is statically determinate II. The truss is kinematically determinate With reference to the above statements, which of the following applies? (a) Both statements are true. (b) Both statements are false. (c) II is true but I false. (d) I is true but II is false. 33 A cantilever beam of length L and a cross section with shape factor f supports a concentrated load P as shown below: figure The length L p of the plastic zone, when the maximum bending moment, equals the plastic moment M p, given by 2.10. For the structure shown below, the vertical deflection at point A is given by 34The ultimate bearing capacity of a soil is 300 kN/m 2. The depth of foundation is 1m and unit weight of soil is 20 kN/m 3. Choosing a factor of safety of 2.5, the net safe bearing capacity is (a) 100 kN/m 2 (c) 80 kN/m 2 (b) 112 kN/m 2 (d) 100.5 kN/m 2 2.12. A deep cut of 1m has to be made in a clay with unit weight 16 kN/m 3 and a cohesion of 25 kN/m 2. What will be the factor of safety if one has to have a slope angle of 30°? Stability number is given to be 0.178 (from Taylor's chart) for a depth factor of 3. (a) 0.80 (c) 1.25 (b) 1.1 (d) 1.0 35 . In a drained triaxial compression test, a saturated specimen of a cohesion less sand fails under a deviatoric stress of 3 kgf/cm 2 when the cell pressure is 1 kgf/cm 2. The effective angle of shearing resistance of sand is about (a) 37° (b) 45° (c) 53° (d) 20° 36Two footings, one circular and the other square, are founded on the surface of a purely cohesion less soil. The diameter of the circular footing is same as that of the side of the square footing. The ratio of their ultimate bearing capacities is (a) 3/4 (b) 4/3 (c) 1.0 (d) 1.3 37. To have zero active pressure intensity at the tip of a wall in cohesive soil, oneshould apply a uniform surcharge intensity of (a) 2 c tan a (b) 2 c cot a (c) - 2 c tan a (d) - 2 c tan a 38. Water flows at a depth of 0.1m with a velocity of 6 m/s in a rectangular channel. The alternate depth is 0.30 m 0.40 m 0.86 m 0.81 m 39. In an area of 200 hectare, water table drops by 4 m. If the porosity is 0.35 and the specific retention is 0.15, change in volume of storage in the aquifer is. (a) 160 m 3 (b) 1.6 x 106 m (c) 8 x 106 m 3 (d) 1.6 x 103 m 3 40. A tube well having a capacity of 4 m 3/hour operates for 20 hours each day during the irrigation season. How much area can be commanded if the irrigation interval is 20 days and depth of irrigation is 7 cm ? (a) 1.71 x 10 4 m 2 (b) 1.14 x 10 4 m 2 (c) 22.9 x 10 4 m 2 (d) 2.29 x 10 4 m 2 41. The parameters in Horton's infiltration equation [f(t) = f c + (f o - f c ) e -kt] are given as, f o = 7.62 cm/hour, f c = 1.34 cm/hour and k = 4.182/hour. For assumed continuous ponding the cumulative infiltration at the end of 2 hours is (a) 2.68 cm (b) 1.50 cm (c) 1.34 cm (d) 4.18 cm 42. Water flows at a rate of 10 m 3/s in a rectangular channel 3 m wide. The critical depth of flow is 1.13 m 2m 1.45 m 1.04 m 43. A circular sewer 2m diameter has to carry a discharge of 2 m 3/s when flowing nearly full. What is the minimum required slope to initiate the flow? Assume Manning's n = 0.015. (a) 0.00023 (b) 0.000036 (c) 0.000091 (d) 0.000014 44. The following characteristics pertain to the sand filters used in water industry. Filtration rate is 1 to 4 m 3/(m 2 day). Typical duration of operation in one run is 24 to 72 hours. Operating cost is low. Which of the above characteristics pertain to slow sand filters? (a) I, II and III (b) I and II (c) II and III (d) I and III 45 The ruling minimum radius of horizontal curve of a national highway in plain terrain for a ruling design speed of 100 km/hour with e = 0.07 and f = 0.15 is close to (a) 250 m (b) 360 m (c) 36 m (d) 300 m 46. Design rate of super elevation for horizontal highway curve of radius 450 m for a mixed traffic condition, having a speed of 125 km/hour is (a) 1.0 (b) 0.05 (c) 0.07 (d) 0.1.54 IRCON Electronics Questions and Answers Ircon Exam paper 1. Speed of the stator field of an Induction motor is (A) Synchronous speed (B) Any speed (C) Less than Synchronous (D) Slip Speed Ans(A) Synchronous speed 2. Difference in speed between stator field and rotor (A) Full load speed (B)No load speed (C)Slip (D) Regulation Ans:(C)Slip 3. FET is advantageous in comparison with BJT because of (A) high input impedance. (B) high gain-bandwidth product. (C) its current controlled behaviour. (D) high noise immunity. Ans: A 4. The emission of electrons in a vacuum diode is achieved by (A) electrostatic field. (B) magnetic field. (C) heating. (D) electron bombardment. Ans: C 5. In a Zener diode large reverse current is due to (A) collision. (B) presence of impurities. (C) rupture of bonds (D) lower resistance in reverse biased region. Ans: D 6. JFET has main drawback of (A) having low input impedance. (B) having high output impedance. (C) being noisy. (D) Having small gain-bandwidth product. Ans: D 7. The CE configuration amplifier circuits are preferred over CB configuration amplifier circuits because they have (A) lower amplification factor. (B) Larger amplification factor. (C) high input resistance and low output resistance. (D) none of these. Ans: B 8. The most commonly used type of electron emission in electron tubes is (A) Photo-electron emission. (B) Thermionic emission. (C) Field emission. (D) Secondary emission. Ans: A 9. After firing an SCR, the gating pulse is removed. The current in the SCR will (A) Remains the same. (B) Immediately fall to zero. (C) Rise up. (D) Rise a little and then fall to zero. Ans: A 10. A device whose characteristics are very close to that of an ideal voltage source is (A) a vaccum diode. (B) a DIAC. (C) a zener diode. (D) a FET. Ans: C 11. Which of the following is a unipolar device? (A) P-N junction diode (B) Zener diode (C) Tunnel diode (D) Schottky diode Ans: D 12. On applying a Positive voltage signal to the base of a normally biased N-P-N CE transistor amplifier (A) Base current will fall. (B) Collector current will fall. (C) Emitter current will fall. (D) Collector voltage will become less positive. Ans: D 13. A switching voltage regulator can be of the following type: (A) step-down (B) step-up (C) inverting (D) none of these Ans: A 14. Avalanche breakdown is primarily dependent on the phenomenon of (A) Collision (B) Doping (C) Ionisation (D) Recombination Ans: D 15. The ripple factor of a power supply is a measure of (A) its voltage regulation. (B) its diode rating. (C) purity of power output. (D) its filter efficiency. Ans: C 16. An N-channel JFET has Pinch-off Voltage of VP = ? 4V and given that VGS = ?1V, then the minimum VDS for the device to operate in the Pinch-off region will be (A) +1V (B) +3V (C) +4V (D) +5V Ans: B 17. The main advantage of flip-flops over transistor circuit is (A) immunity from noise (B) low heating (C) low propagation delay time (D) high propagation. Ans:C 18. The ESC instruction of 8086 may have two formats. In one of the formats, no memory operand is used. Under this format, the number of external op-codes (for the co-processor) which can be specified is? (A) 64 (B) 128 (C) 256 (D) 512 Ans:B 19. The voltage levels for a negative logic system (A) must necessarily be negative (B) could be negative or positive (C) must necessarily be positive (D) must necessarily be either zero or ?5 V Ans:B 20. The TRAP is one of the interrupts available its INTEL 8085. Which one of the following statements is true of TRAP? (A) It is level triggered (B) It is negative edge triggered (C) It is positive edge triggered (D) It is both positive edge triggered and level triggered Ans:D IRCON Electrical Questions and Answers Ircon electrical questions with answers 1. Select the application of fluid coupling fitting from the following: (A) acts as a voltage limiter (B) enables no-load start-up of prime-mover (C) works on the principle of eddy current (D) none of the above Ans:B 2. Application of occupancy sensors is well suited for ___. (A) day light based controllers (B) night based controllers (C) motor controllers (D) movement or noise detector in room space Ans:D 3. When a synchronous motor is running at synchronous speed, the damper winding produces (A) damping torque. (B) eddy current torque. (C) torque aiding the developed torque. (D) no torque. Ans: D 4. If a transformer primary is energised from a square wave voltage source, its output voltage will be (A) A square wave. (B) A sine wave. (C) A triangular wave. (D) A pulse wave. Ans: A 5. The most suitable servomotor for low power applications is (A) a dc series motor. (B) a dc shunt motor. (C) an ac two-phase induction motor. (D) an ac series motor. Ans: B 6. A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is (A) 1500 r.p.m. (B) 1425 r.p.m. (C) 25 r.p.m. (D) 75 r.p.m. Ans: D EX: NS = 120f /P = 120 x 50 /4 =1500rpm N = NS ( 1-s) = 1500 (1-0.05) = 1425 \relative speed = 1500 – 1425 = 75 rpm 7. In a 3-phase synchronous motor (A) the speed of stator MMF is always more than that of rotor MMF. (B) the speed of stator MMF is always less than that of rotor MMF. (C) the speed of stator MMF is synchronous speed while that of rotor MMF is zero. (D) rotor and stator MMF are stationary with respect to each other. Ans: D 8. The synchronous reactance of the synchronous machine is ______________. (A) Ratio between open circuit voltage and short circuit current at constant field current (B) Ratio between short circuit voltage and open circuit current at constant field current (C) Ratio between open circuit voltage and short circuit current at different field current (D) Ratio between short circuit voltage and open circuit current at different field current Ans. A 9. In case of a universal motor, torque pulsation is minimized by _________. (A) load inertia (B) rotor inertia (C) both rotor and load inertia (D) none of the above Ans: C 10. Inverse definite minimum time lag relay is also called ___________ (A) pilot relay. (B) differential relay. (C) over current relay. (D) directional overcurrent relay. Ans: B 11. The direction of rotation of hysteresis motor is reversed by (A) Shift shaded pole with respect to main pole (B) Reversing supply lead (C) Either A or B (D) Neither A nor B Ans: A 12. The short circuit test on a transformer is conducted to obtain (A). copper losses. (B). core loses only. (C). eddy current loss (D). hysteresis loss Ans:A 13. CRGO Steel is used in the core of transformer to reduce (A). Eddy Current loss (B). Ohmic loss (C). both Eddy Current and Hysteresis loss (D). Hysteresis loss Ans:D 14. Two resistances R1 and R2 give combined resistances 4.5O and 1O when they are connected in series and parallel respectively. What would be the values of these resistances ? (A). 3O and 6O (B). 1.5O and 3O (C). 3O and 9O (D). 6O and 9O Ans:B Ex: Here, R1 + R2 = 4.5 ..................(1) and R1.R2/(R1 + R2) = 1 =R1.R2/4.5=1 =R1.R2 = 4.5..................(2) Combining (1) & (2) we get R1 = 1.5 or 3 and R2 = 3 or 1.5 15. Two equal resistors R connected in series across a voltage source V dissipate power P. What would be the power dissipated in the same resistors when they are connected in parallel across the same voltage source ? (A). 4P (B). P (C). 2P (D). 16P Ans:A Ex: Say R is the resistance of the identical two resistors. When they are connected in series across a voltage source V, then total power dissipated by the resistors will be P = V2/2R. When they are connected in parallel across the same voltage source V, then total power dissipated by the resistors will be V2/R/2 = 4V2/2R = 4P. 16. The phase angle difference between current and voltage is 90o, the power will be (A). minimum (B). maximum (C). zero (D). V.I Ans:C Ex: The expression of active power P = V.I.cos?. Where, V is voltage, I is current and ? is the angle between current and voltage. here, this ? = 90o Therefore Power=V.I.Cos 900 = 0[Since, cos 900=0] 17. In a synchronous generator in order to eliminate the fifth harmonic the chording angle should be (A) 9° (B) 18° (C) 27° (D) 36°. Ans:D 18. A hunting sound is produced in a synchronous motor when (A) load fluctuates (B) supply frequency varies (C) both (A) and (B) above (D) none of the above. Ans:C 19. Stampings in transformers are provided to reduce (A) hysteresis loss (B) eddy current loss (C) copper loss (D) all of the above. Ans:B 20. By adding silicon to ferromagnetic , materials (A) electrical resistivity increases and also magnetic permeability increases (B) electrical resistivity decreases and also magnetic permeability increases (C) electrical resistivity decreases and magnetic permeability increases (D) electrical resistivity increases and magnetic permeability decreases. Ans:C