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Chapter 16
ALTERNATING CURRENT
Encircle the most appropriate answer among the following options
1. Alternating current is one which changes in a choose which one is correct:
(a) Magnitude
(b) Direction
(c) Magnitude as well as direction
(d) None of the above
2. The electromagnetic spectrum contains choose which one is correct:
(a) Radio waves
(b) X-rays
(c) Microwaves
(d) All of these
3. Who proved that light waves are electromagnetic?
(a) Faraday
(b) Einstein
(c) Maxwell
(d) Enderson
4. A.C can be measure with the help of choose which one is correct:
(a) Ammeter (D.C)
(b) Moving coil galvanometer
(c) Hot wire ammeter
(d) All of the above
5. Three phase supply also provides choose which one is correct:
(a) 230 V
(b) 460 v
(c) 400 V
(d) None of these
6. Alternating current is converted to direct current by choose which one is correct:
(a) Dynamo
(b) Motor
(c) Transformer
(d) Rectifier
7. If a glass plate is placed between plates of a capacitor, in series with a lighted bulb, the brightness of the bulb.
(a) Remains same
(b) Decreases
(c) Increases
(d) Bulb turns off
8. Electrical resonance in an LCR A.C circuit is very sharp if choose which one is correct:
(a) R is large
(b) R is small
(c) R = XL or Xc
(d) None of these
9. The time during which the voltage sources changes its polarity once is called choose which one is correct:
(a) Time period
(b) Critical time
(c) Period of the AC
(d) None of the above
10. The SI unit of reactance is choose which one is correct:
(a) ohm
(b) Volt — m-1
(c) Volt
(d) Ampere
11 Alternating current or emf measuring instruments measures its choose which one is correct:
(a) r.m.s. value
(b) Peak value
(c) Average value
(d) None of the above
12. The instantaneous voltage across a pure inductance is choose which one is correct:
(a) In phase with current
(b) Lags the current by 900
(c) Leads the current by 900 in phase
(d) None of these
13. One complete set of positive and negative value of alternating quantities is called choose which one is correct:
(a) Frequency
(b) Time period
(c) Amplitude
(d) cycle
14. The process of combining low frequency signal with high frequency radio waves is called choose which one is correct:
(a) Resonance
(b) Fluctuation
(c) Modulation
(d) Amplitude
15. Alternating voltage is choose which one is correct:
(a) Varies inversely with time
(b) Varies directly with time
(c) Independent of time
(d) Varies sinusoidally with time
16. The alternating current can be transmitted choose which one is correct:
(a) Very low cost
(b) To very high cost
(c) Long distances
(d) Both (a) and (c)
17. Alternating current is produced by a voltage source which polarity choose which one is correct:
(a) Keeps on reversing with time
(b) Remains the same
(c) Reverses after period T
(d) None of these
18. For parallel resonant circuit, the resonance current is choose which one is correct:
(a) Zero
(b) Minimum
(c) Maximum
(d) One
19. In L.C parallel circuit, the coil draws choose which one is correct:
(a) Leading current
(b) Lagging voltage
(c) Lagging current
(d) Leading voltage
20. The reciprocal of impedance is called choose which one is correct:
(a) Admittance
(b) Capacitance
(c) Inductance
(d) Resistance
21. The waveform of alternating voltage is the graph between choose which one is correct:
(a) Current and time
(b) Voltage and time
(c) Voltage and current
(d) Voltage along y-axis and time along x-axis
22. The waveform of alternating voltage is a choose which one is correct:
(a) Square
(b) Sinusoidal
(c) Rectangular
None of these
23. The circuit in which current and voltage are in phase, the power factor is choose which one is correct:
(a) Double
(b) three times
(c) One
(d) Zero
24. The average value of alternating voltage over a complete cycle is choose which one is correct:
(a) Zero
(b) 0.7 vmax
(c) 0.707 vmax
(d) None of these
25. The RMS value of alternating voltage is choose which one is correct:
(a) 0.5 times the peak value
(b) 0.7 times the instantaneous value
(c) 0.7 times the peak value
(d) Equal to maximum voltage
26. The alternating voltage or current is actually measured by choose which one is correct:
(a) Its RMS value
(b) Square root of its mean square value
(c) Peak value
(d) Instantaneous value
27. The magnitude of alternating voltage is choose which one is correct:
(a) Always decreases
(b) Always increases
(c) Always remains the same
(d) Does not remain the same
28. The basic circuit element in a D.C circuit is choose which one is correct:
(a) An inductor
(b) A resistor
(c) A capacitor
(d) None of these
29. The basic circuit elements in A.C circuits are choose which one is correct:
(a) Thermistor
(b) Inductor and resistors
(c) Inductor and capacitor
(d) All of above
30. In which of the following, the loss of energy is less choose which one is correct:
(a) Alternating current
(b) Direct current
(c) Photo electric current
(d) None of the above
31. In a resistive A.C circuit, instantaneous values of voltage and current are choose which one is correct:
(a) In phase
(b) Out of phase
(c) Lead each other
(d) None of these
32. At high frequency, the current through a capacitor is choose which one is correct:
(a) Small
(b) Infinity
(c) Zero
(d) Large
33. At what frequency I henry inductance offer same impendance as IF capacitor choose which one is correct:
(a) 450 Hz
(b) 512 Hz
(c) 1 KHz
(d) 159 Hz
34. A transformer has — = 10, the load current is I.0A, the current in primary is choose which one is correct:
(a) 1 A
(b) 0.1 A
(c) 11 A
(d) I0A
35. The reactance of I farad capacitance when connected to D.C circuit is choose which one is correct:
(a) Infinite
(b) One
(c) Zero
(d) None of these
36. When voltage V and current I are in phase the power is expressed as choose which one is correct:
(a) P = VI sin 0
(b) P = I2R
(c) P = VI
(d) P-VIcos0
37. When A.C voltage source is connected to a capacitor choose which one is correct:
(a) Voltage V lags behind current I
(b) Current I leads the voltage V
(c) Voltage leads the current
(d) Both (a) and (b)
38. The measure of the opposition offered by a capacitor to the flow of A.C is called choose which one is correct:
(a) Reactance
(b) Resistance
(c) Impedance
(d) Capacitance
39. Energy in an inductance coil is stored in the form of choose which one is correct:
(a) Electrical energy
(b) Light energy
(c) Magnetic energy
(d) Heat energy
40. The reactance is the ratio of choose which one is correct:
(a) Vrms/lrms
(b) Vrms x lrms
(c) Irms/Vrms
(d) vmaxx V
41. In case of capacitor, the unit of reactance is choose which one is correct:
(a) Farad
(b) Ohm
(c) Newton
(d) All of these
42. The reactance of a coil depends upon choose which one is correct:
(a) Inductance of the coil
(b) Capacitance of the coil
(c) Thickness of the coil
(d) None of these
43. To maintain the current in an inductor, the applied alternating voltage must be choose which one is correct:
(a) Smaller than back emf
(b) Greater than back emf
(c) Equal to back emf
(d) None of these
44. When A.C voltage is applied to an inductor, the choose which one is correct:
(a) Voltage V leads current I by 900
(b) Voltage V leads current I by 2700
(c) Voltage V leads current I by 00
(d) None of these
45. Pure choke consumes choose which one is correct:
(a) Minimum power
(b) Maximum power
(c) No power
(d) Average power
46. Radio frequency choke is choose which one is correct:
(a) Iron cored
(b) Air Cored
(c) Air as well as iron cored
(d) None of these
47. If frequency fis in Hz and inductance L is in milli henry, then XL is in choose which one is correct:
(a) milli ohm
(b) kilo ohm
(c) ohm
(d) none of these
48. If frequency fis in Hz and capacitance C is in F then the unit of Xc is choose which one is correct:
(a) Mega ohm
(b) Milli ohm
(d) None of these
49. Alternating current can be produced by choose which one is correct:
(a) Electric motor
(b) Generator
(c) Turbine
(d) Transformer
50. Which of the following statement is correct for an A.C circuit choose which one is correct:
(a) The current depends upon the components connected in circuit
(b) The current lags the voltage by a phase angle of 900
(c) The current leads the voltage by a phase angle of 900
(d) The current and voltage are in same phase
51. Impedance is the combined effect of choose which one is correct:
(a) Resistance and inductance
(b) Resistance and reactance
(c) Inductance and capacitance
(d) None of these
52. The unit of impedance is choose which one is correct:
(a) Farad
(b) Henry
(c) Tesla
(d) Ohm
53. In an RLC circuit, the impedance is choose which one is correct:
(a) Combined effect of resistance and reactance
(b) Another name of resistance
(c) Another name of inductance and capacitance
(d) None of these
54. The amplitude of the effective current is choose which one is correct:
(a) Irms cos 0
(b) Ims sin0
(c) 10 cos0
(d) Infinity
55. The graph between time and voltage is choose which one is correct:
(a) tan curve
(b) Curved line
(c) Sine curve
(d) Straight line
56. Alternating current can be measured by D.C ammeter because if choose which one is correct:
(a) A.C is virtual
(b) Average current for complete cycle is zero
(c) A.C cannot pass through D.C ammeter
(d) None of the above
57. The highest value reached by the voltage or current in one cycle is known as choose which one is correct:
(a) Peak value
(b) Minimum value
(c) Average value
(d) Zero value
58. Inductive reactance (DL of a coil is expressed in choose which one is correct:
(a) Ohm
(b) Ampere
(c) Volt
(d) None of the above
59. The current flows from O T/2 is choose which one is correct:
(a) + ve direction of A.C
(b) — ve direction of A.C
(c) Towards zero
(d) None of the above
60 The current flows from T/2
(a) — ve direction of A.C
(b) + ve direction of A.C
(c) Towards zero
(d) All of the above
61. The most common source of A.C voltage is choose which one is correct:
(a) Cell
(b) A.C generator
(c) A.C transformer
(d) Motor
62. Voltage drop in A.C circuit is the product of current and choose which one is correct:
(a) Impedance
(b) Inductance
(c) Resistance
(d) None of the above
63. In a purely capacitive A.C circuit, the current is choose which one is correct:
(a) — ve direction of A.C
(b) + ve direction of A.C
(c) Towards zero
(d) All of the above
61. The most common source of A.C voltage is choose which one is correct:
(a) cell
(b) A.C generator
(c) A.C transformer
(d) Motor
62. Voltage drop in A.C circuit is the product of current and choose which one is correct:
(a) Impedance
(b) Inductance
(c) Resistance
(d) None of the above
63. In a purely capacitive A.C circuit, the current is choose which one is correct:
(a) In phase with emf
(b) The ernf by 900
(c) Leads the emf by 900
(d) All of the above
64. With high frequencies, capacitive reactance choose which one is correct:
(a) Remain unchanged
(b) Increases
(c) Decreases
(d) None of the above
65. With increase of frequency of A.C supply, the inductive reactance is choose which one is correct:
(a) Decreases
(b) Increases as square of frequency
(c) Remain unchanged
(d) Increases as directly to frequency
66. A choke is preferred to a capacitor to decrease the A.C in a circuit because the capacitor choose which one is correct:
(a) Has power factor cos = I
(b) May not be a leak proof wattless resistance
(c) Leak proof wattless resistance
(d) None of these
67. With increase in frequency of an A.C supply, the impedance of LCR series circuit choose which one is correct:
(a) Decrease
(b) Increases
(c) Remains constant
(d) First decrease, becomes minimum and then increase
68. SI The unit of impedance is choose which one is correct:
(a) Hertz
(b) Henry
(c) Volt
(d) Ohm
69. The peak value of alternating voltage is 423 volts, its rms value is choose which one is correct:
(a) 300 volts
(b) 423 volts
(c) 150 volts
(d) 211.5 volts
70. The purpose of choke in a fluorescent lamp is choose which one is correct:
(a) Increase the current
(b) Decrease the current
(c) Decrease the voltage
(d) Increase the voltage
71. The power dissipation in a pure inductive or capacitive circuit is choose which one is correct:
(a) Zero
(b) Maximum
(c) Opposite
(d) Negative
72. As series resonance in L.C.R circuit, the impedance is equal to choose which one is correct:
(a) Inductive reactance
(b) Ohmic resistance
(c) Capacitive reactance
(d) None of these
73. In an R.L.C series circuit, the quantities which are directed opposite to each other are choose which one is correct:
(a) Xc and R
(b) Xc and XL
(c) Xc and L
(d) XL and C
74. The condition of resonance in an R.L.C series circuit is that choose which one is correct:
(a) XL = Xc
(b) XL>Xc
(c) XL<Xc
(d) None of these
75. Modulation is the process of choose which one is correct:
(a) Combining low frequency signal with carrier
(b) Separating the low frequency signal from higher frequency radio wave
(c) Combing low frequency signal with high frequency radio waves
(d) Both (a) and (c)
76. Power factor is defined by choose which one is correct:
(a) cos0
(b) sin0
(c) tan0
(d) sec0
77. At resonance frequency, the impedance of an R.L.C series circuit is choose which one is correct:
(a) Minimum
(b) Zero
(c) Maximum
(d) None of these
78. At resonance frequency in an R.L.C series circuit, VL and Vc choose which one is correct:
(a) Greater than the source voltage
(b) Smaller than the source voltage
(c) Equal to source voltage
(d) None of these
79. A.C voltmeter measures choose which one is correct:
(a) Peak value
(b) Average voltage
(c) Peak inverse voltage
(d) r.m.s voltage
80. For modulation purpose, high frequency radio waves are called choose which one is correct:
(a) Carrier waves
(b) Transverse waves
(c) Radio waves
(d) Longitudinal waves
81. The positive value of current and voltage over a cycle is choose which one is correct:
(a) Positive
(b) Zero
(c) Negative
(d) None of the above
82. The low frequency signal used for modulation is called choose which one is correct:
(a) Carrier signal
(b) Radio signal
(c) Modulating signal
(d) None of these
82. A capacitor is a perfect insulator for choose which one is correct:
(a) Direct current
(b) Alternating current
(c) Both (a) and (b)
(d) None of above
83. In comparison to D.C transmission losses in A.C are choose which one is correct:
(a) Low
(b) High
(c) Negligible
(d) None of the above
84. In A.C circuits, the A.C instruments indicate choose which one is correct:
(a) Peak values
(b) Square ofpeak values
(c) Square root of peak values
(d) Virtual values
85. When resistance is increased in a series LCR circuit choose which one is correct:
(a) Impedance decreases
(b) Reactance increases
(c) Phase angle increases
(d) phase angle decreases
86. The amplitude modulation A.M transmission frequencies range from choose which one is correct:
(a) 540 Hz to 1600 Hz
(b) 540 Hzto 1500 MHz
(c) 540 KHz to 1600 KHz
(d) None of these
87. In frequency modulation, the amplitude of carrier waves is choose which one is correct:
(a) Increases
(b) Remains constant
(c) Decreases
(d) None of these
88. Which current can pass through a capacitor continuously choose which one is correct:
(a) Direct current
(b) Electronic current
(c) Alternating current
(d) Both (a) and (b)
89. An inductor may store energy in its choose which one is correct:
(a) Magnetic field
(b) Electric field
(c) coil
(d) None of the above
90. Modulation is achieved by changing the choose which one is correct:
(a) Frequency and amplitude of the carrier waves
(b) Only frequency of the carrier wave
(c) Only amplitude of the carrier wave
(d) None of these
91. A device that allows only the continuous flow of AC through a circuit is choose which one is correct:
(a) Capacitor
(b) Inductor
(c) Dynamo
(d) D.C motor
92. A.C varies as function of choose which one is correct:
(a) Time
(b) Voltage
(c) Current
(d) Displacement
93. In electromagnetic waves, the electric and magnetic fields are choose which one is correct:
(a) Perpendicular
(b) Parallel
(c) Antiparallel
(d) At an angle of 450
94. If frequency of rotating coil of an A.C. generator is f Hz then frequency of e.m.f. produced is choose which one is correct:
(a) 50 Hz
(b) 60 Hz
(c) fHz
(d) None of these
95. The basic circuit element in a D.C. circuit is choose which one is correct:
(a) Capacitor
(b) Transistor
(c) Resistor
(d) Inductor
96. In modulation, low frequency signal is known as choose which one is correct:
(a) Loaded signal
(b) Fluctuated signal
(c) Harmonic signal
(d) Modulation signal
97. As a result of modulation, the resultant wave is known as choose which one is correct:
(a) Energetic carriers wave
(b) Carrier wave
(c) Modulated carrier wave
(d) None of the above
98. For q – t graph, slope shows choose which one is correct:
(a) Current
(b) Voltage
(c) e.m.f.
(d) None of these
99. In A.C circuits, current and voltage is controlled by choose which one is correct:
(a) Inductor L
(b) Resistance R
(c) Capacitance C
(d) All of the above
100. A pure inductive coil is that which has choose which one is correct:
(a) No impedance
(b) No ohmic resistance
(c) Some ohmic resistance
(d) None of these