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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 = X_{L }or X_{c}

(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 â€” 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 v_{max}

(c) 0.707 v_{max}

(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 â€” = 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 = I ^{2}R **

(c) P = VI

(d) P-VIcos~~0~~

*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) V _{rms}/l_{rms} **

(b) V_{rms }x l_{rms}

(c) I_{rms}/V_{rms}

(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 X*_{c}* 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) I _{rms} cos 0**

(b) I_{ms} sin~~0~~

(c) 1_{0} cos~~0~~

(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) â€” ve direction of A.C

(c) Towards zero

(d) None of the above

*60 The current flows from T/2*

**(a) â€” 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) â€” 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) X_{c} and R

(b) X_{c} and X_{L}

(c) X_{c} and L

(d) X_{L} and C

*74. The condition of resonance in an R.L.C series circuit is that choose which one is correct:*

**(a) X _{L }= X_{c}**

(b) X_{L}>X_{c}

(c) X_{L}<X_{c}

(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) cos 0 **

(b) sin~~0~~

(c) tan~~0~~

(d) sec~~0~~

*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 45^{0}

*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