Weekly exam 2

Electronics EngineeringCERTCWeekly Exam 2ELEX

Instruction: Select the correct answer for each of the following questions. Mark only one answer for each item by shading the box corresponding to the letter of your choice on the answer sheet provided.

Strictly no erasures allowed. Use pencil no. 1 only.NOTE:Whenever you come across a caret (^) sign, it means exponentiation.

1. Carbon-composition resistorsA. can handle gigantic levels of power.B. have capacitance or inductance along with resistance.C. have essentially no capacitance or inductance.*D. work better for ac than for dc.

2. What type of resistor, or combination of resistors, would you use as the meter-sensitivity control in a test instrument, when continuous adjustment is desired?A. A set of switchable, fixed resistorsB. A linear-taper potentiometer*C. An audio-taper potentiometerD. A wirewound resistor

3. Suppose a 1-k resistor will dissipate 1.05 W, and you have a good supply of 1-W resistors of various ohmic values. If theres room for 20 percent resistance error, the cheapest solution is to useA. four 1-k, 1-W resistors in series-parallel.B. a pair of 2.2-k, 1-W resistors in parallel.*C. a set of three 3.3-k, 1-W resistors in parallel.D. a single 1-k, 1-W resistor, because all manufacturers allow for a 10 percent margin of safety when rating resistors for their power-handling capability.

4. A ferromagnetic core is placed in an inductor mainly toA. increase the current carrying capacity.B. increase the inductance.*C. limit the current.D. reduce the inductance.

5. As an inductor core material, airA. has excellent efficiency.*B. has high permeability.C. allows large inductance to exist in a small volume.D. has permeability that can vary over a wide range.

6. Which of the following is not a characteristic of mica capacitors?A. Excellent efficiencyB. Small size, even for large values of capacitance*C. High voltage-handling capacityD. Low loss

7. A carbon-film resistor is color coded with red, violet, black, and gold stripes. What are its resistance and tolerance?A. 27 5%*C. 270 10%B. 270 5%D. 27 10%

8. What is the area in circular mils (cmils) of a wire whose diameter, d, is 0.01 in.?A. 0.001 cmilC. 1 cmilB. 10 cmilD. 100 cmil*

9. One of the main applications of a capacitor is toA. block ac and pass dcC. block dc and pass ac*B. block both dc and acD. pass both dc and ac

10. Two 0.02- F, 500-V capacitors in series have an equivalent capacitance and breakdown voltage rating ofA. 0.04 F, 1 kVC. 0.01 F, 500 VB. 0.01 F, 250 VD. 0.01 F, 1 kV*

11. How much is the inductance of a coil that induces 50 V when its current changes at the rate of 500 A/s?A. 100 mH*C. 100 HB. 1 HD. 10 H

12. It is found that the resistance of a coil of wire increases from 40 ohm at 15C to 50 ohm at 60C. Calculate the resistance temperature coefficient at 0C of the conductor material.A. 1/40 per CC. 1/165 per C*B. 1/50 per CD. 1/234.5 per C

13. An electric radiator is required to dissipate 1kW when connected to a 230 V supply. If the coils of the radiator are of wire 0.5 mm in diameter having resistivity of 60 -cm, calculate the necessary length of the wire.A. 13.27 mC. 15.65 mB. 17.32 m*D. 16.45 m

14. An air capacitor has two parallel plates 10cm2 and 0.5 cm apart. When a dielectric slab of area 10cm2 and thickness 0.4 cm was inserted between the plates, one of the plates has to be moved by 0.4 cm to restore the capacitance. What is the dielectric constant of the slab?A. 3C. 4B. 5*D. 6

15. A multiple plate capacitor has 10 plates, each of area 10 square cm and separation between 2 plates is 1 mm with air as dielectric. Determine the energy stored when voltage of 100 volts is applied across the capacitor.A. 0.3985 J*C. 97.7 pJB. 79.7 pJD. 0.5294 J

16. Two similar coils have a coupling coefficient of 0.25. When they are connected in series cumulatively, the total inductance is 80 mH. Calculate the self inductance of each coil.A. 48 mHC. 40 mHB. 32 mH*D. 20 mH

17. A rectangular carbon block has dimensions 1.0 cm x 1.0 cm x 50 cm. What is the resistance measured between the two square ends? Resistivity of carbon at 20C is 3.5 x 10-5 -m.A. 0.350C. 0.530B. 0.175*D. 0.715

18. A parallel plate capacitor has the following values: k = 60, d = 0.025 inches, A = 6 square inches. What is the capacitance of the capacitor?A. 32.39 picofaradC. 4372 picofaradB. 3239 picofarad*D. 437.2 picofarad

19. A capacitor consists ofA. two insulators separated by a conductorB. a coil of wire wound on an iron coreC. two conductors separated by an insulator*D. none of the above

20. Capacitance increases withA. larger plate area and greater distance between the platesB. smaller plate area and greater distance between the platesC. larger plate area and less distance between the plates*D. higher values of applied voltage

21. A fluctuating magnetic fieldA. produces an electric current in an insulator.B. magnetizes the earth.C. produces a fluctuating electric field.*D. results from a steady electric current.

22. A span of wire 1 km long has a conductance of 0.9 S. What is the conductance of a span of this same wire that is 3 km long?A. 1.8 SC. 0.2 SB. 0.3 S*D. 2.7 S

23. A bleeder resistorA. is connected across the capacitor in a power supply.*B. keeps a transistor from drawing too much current.C. prevents an amplifier from being overdriven.D. optimizes the efficiency of an amplifier.

24. An advantage of ac over dc in utility applications is the fact thatA. ac is easier to transform from one voltage to another.*B. ac is transmitted with lower loss in wires.C. ac can be easily obtained from dc generators.D. ac can be generated with less-dangerous by-products.

25. The wavelength of a 500-Hz sound wave isA. 60 kmC. 4.52 ftB. 2.26 ft*D. 0.226 ft

26. In residential house wiring, the neutral wire is always color-codedA. blackC. greenB. bare copperD. white*

27. How much is the capacitance, C, of a capacitor that draws 4.8 mA of current from a 12-Vac generator? The frequency of the ac generator is 636.6 Hz.A. 0.01 FC. 0.001 FB. 0.1 F*D. 100 pF

28. For a capacitor, the charge and discharge current, Ic,A. lags the capacitor voltage, Vc, by a phase angle of 90B. leads the capacitor voltage, Vc, by a phase angle of 90*C. is in phase with the capacitor voltage, VcD. none of the above

29. For a steady dc current, the XL of an inductor isA. infiniteC. usually about 10 k*B. extremely highD. 0 *

30. If the dielectric material between the plates of a capacitor is changed, all other things being equal,A. the value of XC increases negatively.B. the value of XC decreases negatively.C. the value of XC does not change.D. we cannot say what happens to XC without more data.*

31. Imagine a coil, a resistor, and a capacitor connected in parallel. The resistance is 1.0 , the capacitive susceptance is 1.0 S, and the inductive susceptance is 1.0 S. Then, suddenly, the frequency is cut to half its former value. What is the complex admittance at the new frequency?A. 1.0 + j0.0C. 1.0 j1.5*B. 1.0 + j1.5D. 1.0 j2.0

32. Suppose the apparent power in a circuit is 100 W, and the imaginary power is 40 W. What is the true power?A. 92 W*C. 140 WB. 100 WD. 60 W

33. A branch current of + j 250 mA representsA. 250 mA of inductive currentC. 250 mA of capacitive current*B. 250 mA of resistive currentD. 250 mA of in-phase current

34. Four coils are connected in series. Each has induced in it a sinusoidal emf of 100V, 50 Hz and there is a phase difference of 14 electrical degrees between one coil and the next. What is the total emf generated in the circuit?A. 483 VC. 384 V*B. 348 VD. 438 V

35. Work equal to 136.0 joules is expended in moving 8.5 x 1018 electrons between two points in an electric circuit. What potential difference does this establish between the two points?A. 50 VC. 150 VB. 100 V*D. 200 V

36. Electrical energy is converted to heat at the rate of 7.56kJ/min in a resistor which has 270 C/min passing through. What is the voltage difference across the resistor terminals?A. 2041 VC. 82 VB. 4021 VD. 28 V*

37. How many electrons pass a fixed point in a 100-watt light bulb in 1 hour if the applied constant voltage is 120 V?A. 1.87 x 1022*C. 2.69 x 1022B. 5.20 x 1018D. 7.49 x 1018

38. A series RLC circuit, with R = 15, L = 80 mH, and C = 30 F, has a sinusoidal current at angular frequency 500 rad/s. Determine the phase angle and whether the current leads or lags the total voltage.A. 60.6 leadsC. 45.2 leadsB. 60.6 lags*D. 45.2 lags

39. Find Z in the parallel circuit of the figure below, if V = 50 30 V and I = 27.9 57.8 A.

A. 5 -30*C.7.18-27.8B. 1.78 -27.8D. 3.45 39

40. A 4500-VA load at power factor 0.75 lagging is supplied by a 60-Hz source at effective voltage 240 V. Determine the parallel capacitance in microfarads necessary to improve the power factor to 0.9 lagging.A. 212 FC. 61.8 F*B. 122 FD. 18.6 F

41. Two heaters A and B are in parallel across supply voltage V. Heater A produces 500 kcal in 200 min and B produces 1000 kcal in 10 min. The resistance of A is 10 ohms. What is the resistance of B?A. 10 ohmsC. 2.5 ohms*B. 5 ohmsD. 7.5 ohms

42. For a given line voltage, four heating coils will produce maximum heat when connectedA. all in parallel*B. all in seriesC. with two parallel pairs in seriesD. one pair in parallel with the other two in series

43. The rms value of a sinusoidal ac current is equal to its value at an angle of ___ degreesA. 60C. 30B. 45*D. 90

44. A conductor has how many types of flow?A. 1*C. 3B. 2D. 4

45. What is meant by back emf?A. a voltage that is applied in the reverse directionB. an emf that is due to flywheel effectC. an emf that is generated from the back of an electromagnetD. a voltage that opposes the applied emf

46. Capacitive reactance, XC,A. applies only to nonsinusoidal waveforms or dcB. applies only to sine waves*C. applies to either sinusoidal or nonsinusoidal waveformsD. is directly proportional to frequency

47. Two capacitors are in series across a 50-V source. If one is 1-F capacitor with 16 V across it, what is the capacitance of the other?A. 0.147 FC. 0.741 FB. 0.471 F*D. 0.174 F

48. A 3-H inductor has 2000 turns. How many turns must be added to increase the inductance to 5 H?A. 582*C. 1582B. 2582D. 3582

49. What is the shortest time required for a 2.1 krad/s sinusoid to increase from zero to four-fifths of its peak value?A. 0.381 msC. 0.553 msB. 0.476 msD. 0.442 ms*

50. At the same frequency, a larger capacitance providesA. more charge and discharge currentB. less charge and discharge currentC. less capacitive reactance, XCD. both a and c*

51. Movement of holes in a semiconductorA. is like a flow of electrons in the same direction.B. is possible only if the current is high enough.C. results in a certain amount of electric current.*D. causes the material to stop conducting.

52. Which of the following units can represent magnetic flux density?A. The volt-turnC. The gauss*B. The ampere-turnD. The gauss-turn

53. A coil has 500 turns and carries 75 mA of current. The magnetomotive force isA. 37,500 At.C. 37.5 At.*B. 375 At.D. 3.75 At.

54. A metal-film resistorA. is made using a carbon-based paste.B. does not have much inductance.*C. can dissipate large amounts of power.D. has considerable inductance.

55. A resistor is specified as having a value of 68 , but is measured with an ohmmeter as 63 . The value is off by which of the following percentages?A. 7.4%*C. 5%B. 7.9%D. 10%

56. If a wire coil has 100 turns and carries 1.30 A of current, what is the magnetomotive force?A. 130 GbC. 164 Gb*B. 76.9 GbD. 61.0 Gb

57. The temperature coefficient of resistance of semiconductors isA. positiveC. negative*B. zeroD. infinite

58. A platinum coil has a resistance of 3.146 at 40C and 3.767 at 100C. Find the resistance at 0C.A. 7.322C. 2.732*B. 3.272D. 7.333

59. What do you call an electronic component that is non-linear resistor and its resistance is a function of the voltage across it?A. Varistor*C. ThyristorB. ICD. Triac

60. If the value of 0 of a conductor is 1/234 per C, then the value of 18 is?A. 1/218 per CC. 1/272 per CB. 1/252 per C*D. 1/245 per C

61. A rectangular carbon block has dimensions 1.0 cm x 1.0 cm x 50 cm. What is the resistance measured between the two square ends? Resistivity of carbon at 20C is 3.5 x 10-5 -m.A. 0.350C. 0.530B. 0.175*D. 0.715

62. One precaution to observe when checking resistors with an ohmmeter is toA. check high resistances on the lowest ohms range.B. check low resistances on the highest ohms range.C. disconnect all parallel paths.*D. make sure your fingers are touching each test lead.

63. If a thermistor has a negative temperature coefficient (NTC), its resistanceA. increases with an increase in operating temperature.B. decreases with a decrease in operating temperature.C. decreases with an increase in operating temperature.*D. is unaffected by its operating temperature.

64. Which has more resistance, a 100-ft length of No. 12 gage copper wire or a 100-ft length of No. 12 gage aluminum wire?A. The 100-ft length of No. 12 gage aluminum wire.*B. The 100-ft length of No. 12 gage copper wire.C. They both have exactly the same resistance.D. It cannot be determined.

65. The term pole as it relates to switches is defined asA. the number of completely isolated circuits that can be controlled by the switch.*B. the number of closed contact positions that the switch has.C. the number of connecting terminals the switch has.D. none of the above.

66. What is the name for a nonmetallic material that has the ferromagnetic properties of iron?A. lodestoneC. ferrite*B. toroidD. solenoid

67. Hysteresis lossesA. increase with higher frequencies.*B. decrease with higher frequencies.C. are greater with direct current.D. increase with lower frequencies

68. The saturation of an iron core occurs whenA. all of the molecular dipoles and magnetic domains are aligned by the magnetizing force.B. the coil is way too long.C. the flux density cannot be increased in the core when the field intensity is increased.D. both a and c.*

69. A vertical wire with electron flow into this page has an associated magnetic field which isA. clockwiseC. parallel to the wireB. counterclockwise*D. none of the above

70. How much is the induced voltage when a magnetic flux cuts across 150 turns at the rate of 5 Wb/s?A. 7.5 kVC. 750 V*B. 75 VD. 750 mV

71. An electric radiator is required to dissipate 1kW when connected to a 230 V supply. If the coils of the radiator are of wire 0.5 mm in diameter having resistivity of 60 -cm, calculate the necessary length of the wire.A. 13.27 mC. 15.65 mB. 17.32 m*D. 16.45 m

72. Two heaters A and B are in parallel across a supply voltage V. Heater a produces 500 kcal in 20 minutes and B produces 1000 kcal in 10 minutes, the resistance of A is 10 Ohm. What is the resistance of B?A. 2.5 ohms*C. 3.5 ohmsB. 4.5 ohmsD. 0.14 ohms

73. Find the output of four lead acid cells.A. 1.6 VC. 3.2 VB. 5.8 VD. 8.4 V*

74. What do you call the force that sets up or tends to set up magnetic flux in a magnetic circuit?A. Dynamic ForceC. Potential DifferenceB. Electromotive ForceD. Magnetomotive Force*

75. What is the lagging effect between the magnetizing force applied and flux density?A. Hysteresis*C. ReluctanceB. PermeanceD. Eddy current

76. In order to match the load to the generator means making the load resistance _______.A. decreasedB. equal to generators internal resistance*C. lowered than generators internal resistanceD. increased to more generators internal resistance

77. A good material conductor should have _______ valence electrons.A. 1*C. 10B. 21D. 3.5

78. Given two voltages: S (t) = 10 cos (wt + 30) volts and Q (t) = 15 cos (wt + 45).Find V (t) = S (t) + QA. V (t) = 25 cos (wt + 75) voltsB. V (t) = 5.9 cos (wt + 71) voltsC. V (t) = 24.8 cos (wt + 39) volts*D. V (t) = 13.6 cos (wt + 75) volts

79. What is the unit of magnetic flux in S1 system?A. TeslaC. GaussB. Weber*D. Maxwell

80. What law in electronic where an induced current will be in such a direction that its own magnetic opposes the magnetic field that produces the same?A. Lenzs Law*C. Nortons LawB. Maxwells LawD. Electromagnetic Law

81. Solve the flux density given a magnetic flux of 5,000 Mx through a perpendicular area of 2 cm by 5A. 50 GC. 500 G*B. 5,000 GD. 10,000 G

82. When a power supply is constructed to operate from either 240-V or 120-V ac lines, such that it will have same secondary output, its primary when connected from 240 V must be _______.A. connected in seriesB. connected in parallelC. split into halves and connected in series*D. split into halves and connected in parallel

83. A law that states that the current in a thermionic diode varies directly with the three-halves power of anode voltage and inversely with the square of the distance between the electrodes, provided operating conditions are such that the current is limited only by the space charge.A. Halls lawC. Joules lawB. Childs law*D. Coulombs law

84. Materials whose permeabilities are slightly greater than that of free spaceA. Paramagnetic*C. FerromagneticB. Non- magneticD. Diamagnetic

85. It is the reciprocal of reluctance and implies the case of readiness with which magnetic flux is developed. A. ResistanceC. Permeance*B. ConductanceD. Inductance

86. A t/m is a unit ofA. MmfC. ReluctanceB. EmfD. Magnetizing force*

87. Calculate the flux density that will be produced by the field intensity of 2000 a. t/m for a permeability of 126 x 10^-6 T/A.t/mA. 0.252 GC. 0.252 T*B. 0.252 x 10^-2 TD. 0.252 x 10^-2 G

88. A point charge, Q=30nC is located at the origin in Cartesian coordinates. Find the electric flux density D at (1,3-4) m.A. 12.7pC/m^2C. 19.8 pC/m^2*B. 18.5pC/m^2D. 15.6 pC/m^2

89. Ten identical charges of 500uC each are spaced equally around a circle of radius 2. Find the force on a charge of -20uC located on the axis, 2m from the plane of circle.A. -97.5 an NC. 79.5 an NB. 97.5 an ND. -79.5 an N*

90. What is the SI base unit of EMF?A. *C. B. D.

91. The statement The emf, E induced in a circuit is directly proportional to the time rate of change of the magnetic flux through the circuit is known asA. Lenz LawC. Faradays First LawB. Faradays Second LawD. Faradays Law of Induction*

92. What is the power dissipated by R2, R4, and R6?

A. P2 = 417 mW, P4 = 193 mW, P6 = 166 mW *B. P2 = 407 mW, P4 = 183 mW, P6 = 156 mWC. P2 = 397 mW, P4 = 173 mW, P6 = 146 mWD. P2 = 387 mW, P4 = 163 mW, P6 = 136 mW

93. Find the equivalent resistance of

A. 30 ohmsC. 50 ohmsB. 40 ohms*D. 60 ohms

94. Which circuit fault do the meter readings in the given figure indicate?

A. The 1 kresistor is shorted.B. The 4.7 kresistor is shorted.C. The 2.2 kresistor is shorted.D. The 3.3 kresistor is shorted.*

95. In the given circuit, what isRUNKequal to ifRVmust be adjusted to 1,232in order to balance the bridge?

A. 220 *C. 6,899B. 1232D. 7890

96. What determines if resistor connections are in series, parallel, or seriesparallel?A. Voltage sourceC. resistanceB. Power sourceD. current flow*

97. Which component is shorted?

A. R1C. R2B. R3D. R4*

98. Which of the following dependent sources is considered as a transconductance circuit?A. VCVSC. CCVS*B. VCCSD. CCCS

99. If there are 28 branches and 6 nodes in a certain circuit, how many independent loops or mesh loops can be made the circuit?A. 22C. 24B. 23*D. 25

100. The circuit below is referred to as a bridge circuit and is used extensively in electronic and scientific instruments. Calculate the current I and the voltage Vabwhen Rx=0 ohms.

A. 45.5 mAC. 43.3 mAB. 44.4 mAD. 42.2 mA *

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