12th Class Physics Alternating Current / प्रत्यावर्ती धारा Question Bank

done MCQ - Alternating Currents Total Questions - 125

• question_answer1)
  Alternating current cannot be measured by DC ammeter because:
  A)
  AC cannot pass through DC ammeter done clear
  B)
  AC changes direction done clear
  C)
  average value of current for complete cycle is zero done clear
  D)
  DC ammeter will get damaged done clear
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• question_answer2)
  The sum of average current values over on complete cycle is:
  A)
  negative                         done clear
  B)
  positive done clear
  C)
  zero                  done clear
  D)
  Both a. and b. done clear
  View Solution play_arrow

• question_answer3)
  Alternating voltage (V) is represented by the equation:
  A)
  \[V(t)={{V}_{m}}{{e}^{\omega t}}\]               done clear
  B)
  \[V(t)={{V}_{m}}\sin \,\omega t\] done clear
  C)
  \[V(t)={{V}_{m}}\cot \,\omega t\]          done clear
  D)
  \[V(t)={{V}_{m}}tan\,\omega t\] where \[{{V}_{m}}\] is the peak voltage done clear
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• question_answer4)
  A \[100\text{ }\Omega \]resistor is connected to a 220 V, 50 Hz AC supply. The rms value of current in the circuit is:
  A)
  1.56 A                           done clear
  B)
  1.56 mA done clear
  C)
  2.2 A                done clear
  D)
  2.2 mA done clear
  View Solution play_arrow

• question_answer5)
  An alternating current is given by \[l={{l}_{1}}\cos \omega t+{{l}_{2}}\sin \omega t\]. The root mean square current is given by:
  A)
  \[\frac{\left( {{l}_{1}}+{{l}_{2}} \right)}{\sqrt{2}}\]                   done clear
  B)
  \[\frac{{{\left( {{l}_{1}}+{{l}_{2}} \right)}^{2}}}{2}\] done clear
  C)
  \[\sqrt{\frac{l_{1}^{2}+l_{2}^{2}}{2}}\]                    done clear
  D)
  \[\frac{\sqrt{l_{1}^{2}-l_{2}^{2}}}{2}\] done clear
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• question_answer6)
  The peak voltage of an AC supply is 440 V, then its rms voltage is:
  A)
  31.11 V                         done clear
  B)
  311.1 V done clear
  C)
  41.11 V                         done clear
  D)
  411.1 V done clear
  View Solution play_arrow

• question_answer7)
  The rms value of current in an AC circuit is 25 A, then peak current is:
  A)
  35.36 mA                      done clear
  B)
  35.36 A done clear
  C)
  3.536 A                         done clear
  D)
  49.38 A done clear
  View Solution play_arrow

• question_answer8)
  An alternating voltage given by \[V=140\,\,sin\,\,314t\]is connected across a pure resistor of \[50\text{ }\Omega \], the rms current through the resistor is:
  A)
  1.98 A                           done clear
  B)
  5.63 A done clear
  C)
  8.43 A                           done clear
  D)
  2.39 A done clear
  View Solution play_arrow

• question_answer9)
  If the rms current in a 50 Hz AC circuit is 5 A. the value of the current 1/300 seconds after its value becomes zero is:                                                                                             (NCERT EXEMPLAR)
  A)
  \[5\sqrt{2}\,A\]               done clear
  B)
  \[5\sqrt{\frac{3}{2}}\,A\] done clear
  C)
  \[\frac{5}{6}A\]                         done clear
  D)
  \[\frac{5}{\sqrt{2}}A\] done clear
  View Solution play_arrow

• question_answer10)
  When an AC is connected to a resistor what is the phase difference between the current and voltage?
  A)
  \[90{}^\circ \]                           done clear
  B)
  \[180{}^\circ \] done clear
  C)
  \[0{}^\circ \]                             done clear
  D)
  \[60{}^\circ \] done clear
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• question_answer11)
  In a purely resistive AC circuit, the current:
  A)
  is in phase with the e.m.f. done clear
  B)
  leads the e.m.f. by a difference of \[\pi \] radian phase done clear
  C)
  leads the e.m.f. by a phase difference of \[\pi /2\] radians done clear
  D)
  lags behind the e.m.f. by phase difference of \[\pi /4\] radians done clear
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• question_answer12)
  The voltage over a cycle varies as \[V={{V}_{0}}\sin \omega t\] for \[0\le t\le \frac{\pi }{\omega }\] \[=-{{V}_{0}}\sin \omega t\] for \[\frac{\pi }{\omega }\le t\le \frac{2\pi }{\omega }\] The average value of the voltage for one cycle is:
  A)
  \[\frac{{{V}_{0}}}{\sqrt{2}}\]                           done clear
  B)
  \[\frac{{{V}_{0}}}{2}\] done clear
  C)
  zero                               done clear
  D)
  \[\frac{2{{V}_{0}}}{\pi }\] done clear
  View Solution play_arrow

• question_answer13)
  The rms value of potential difference V as shown in the figure is:
  A)
  \[\frac{{{V}_{0}}}{\sqrt{3}}\]                           done clear
  B)
  \[{{V}_{0}}\] done clear
  C)
  \[\frac{{{V}_{0}}}{\sqrt{2}}\]                           done clear
  D)
  \[\frac{{{V}_{0}}}{2}\] done clear
  View Solution play_arrow

• question_answer14)
  The relation between an AC voltage source and time in SI units is \[V=120\,\sin \,\,(100\pi t)\,\,cos\,\,(100\pi t)V\]. The value of peak voltage and frequency will be respectively:
  A)
  120 V and 100 Hz     done clear
  B)
  \[\frac{120}{\sqrt{2}}V\]and 100 Hz done clear
  C)
  60 V and 200 Hz     done clear
  D)
  60 V and 100 Hz done clear
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• question_answer15)
  A light bulb is rated at 100 W for a 220 V AC supply. The resistance of the bulb is:
  A)
  \[284\,\Omega \]             done clear
  B)
  \[384\,\Omega \] done clear
  C)
  \[484\,\Omega \]             done clear
  D)
  \[584\,\Omega \] done clear
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• question_answer16)
  An AC source is of \[\frac{200}{\sqrt{2}}V,\,50\,Hz\]. The value of voltage after \[\frac{1}{600}s\] from the start is:
  A)
  \[200\,V\]                       done clear
  B)
  \[\frac{200}{\sqrt{2}}V\] done clear
  C)
  \[100\,V\]                       done clear
  D)
  \[50\,V\] done clear
  View Solution play_arrow

• question_answer17)
  The peak value of domestic AC supply voltage is 325 V. What is the rms value?
  A)
  325 V                            done clear
  B)
  230 V   done clear
  C)
  200 V                            done clear
  D)
  325 V done clear
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• question_answer18)
  The equation of AC is given by \[l~=100\text{ }\sin \text{ }314t.\] What is the frequency?
  A)
  314 Hz                          done clear
  B)
  100 Hz   done clear
  C)
  50 Hz                            done clear
  D)
  100 Hz done clear
  View Solution play_arrow

• question_answer19)
  The line that draws power supply to your house from street has:
  A)
  \[220\sqrt{2}\,V\]average voltage done clear
  B)
  220 V average voltage done clear
  C)
  voltage and current out of phase by \[\pi /2\] done clear
  D)
  voltage and current possibly differing in phase \[\phi \] such that \[|\phi |<\frac{\pi }{2}\] done clear
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• question_answer20)
  When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of 220 V. This means:                                                                              (NCERT EXEMPLAR)
  A)
  input voltage cannot be AC voltage, but a DC voltage done clear
  B)
  maximum input voltage is 220 V done clear
  C)
  the meter reads not V but \[<{{V}^{2}}>\] and is calibrated to read \[\sqrt{<{{V}^{2}}>}\] done clear
  D)
  the pointer of the meter is stuck by some mechanical defect done clear
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• question_answer21)
  An   AC   source   of   voltage \[V={{V}_{m}}\sin \,\omega t\] is connected across the resistance R as shown in figure. The phase relation between current and voltage for this circuit is:         
  A)
  both are in phase done clear
  B)
  both are out of phase by \[90{}^\circ \] done clear
  C)
  both are out of phase by \[120{}^\circ \] done clear
  D)
  both are out of phase by \[180{}^\circ \] done clear
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• question_answer22)
                       In an AC circuit, V and l are given by \[V=150\,\sin \,(150t)V\] and \[l=150\,\sin \,\left( 150\,t+\frac{\pi }{3} \right)A\]. The power dissipated in the circuit is:
  A)
  106 W              done clear
  B)
  150 W done clear
  C)
  5625 W                         done clear
  D)
  zero   done clear
  View Solution play_arrow

• question_answer23)
  The phase relationship between current and voltage in a pure resistive circuit is best represented by:
  A)
         done clear
  B)
  done clear
  C)
         done clear
  D)
  done clear
  View Solution play_arrow

• question_answer24)
  The projection of a phasor on any axis, always represents the:
  A)
  rms value of a quantity done clear
  B)
  peak value of a quantity done clear
  C)
  mean value of a quantity done clear
  D)
  instantaneous value of a quantity done clear
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• question_answer25)
  The time axis of an AC phasor represents:
  A)
  time                  done clear
  B)
  phase angle done clear
  C)
  voltage                          done clear
  D)
  current done clear
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• question_answer26)
  A phasor is a:
  A)
  scalar quantity                done clear
  B)
  vector quantity done clear
  C)
  tensor quantity               done clear
  D)
  None of these done clear
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• question_answer27)
  In the case of an inductor:
  A)
  voltage lags the current by \[\frac{\pi }{2}\] done clear
  B)
  voltage leads the current by \[\frac{\pi }{2}\] done clear
  C)
  voltage leads the current by \[\frac{\pi }{3}\] done clear
  D)
  voltage leads the current by \[\frac{\pi }{4}\] done clear
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• question_answer28)
  An alternating voltage \[V={{V}_{0}}\sin \,\omega t\] is applied across a circuit. As a result, the current \[l={{l}_{0}}\sin \,(\omega t-\pi /2)\] flows in it. The power consumed in the circuit per cycle is:
  A)
  \[0.5\,{{V}_{0}}{{l}_{0}}W\]                done clear
  B)
  \[0.707\,{{V}_{0}}{{l}_{0}}W\] done clear
  C)
  \[1.919\,{{V}_{0}}{{l}_{0}}W\]                        done clear
  D)
  zero done clear
  View Solution play_arrow

• question_answer29)
  An ideal inductor is in turn put across 220V, 50 Hz and 220 V. 100 Hz supplies. The current flowing through it in the two cases will be:
  A)
  equal                             done clear
  B)
  different done clear
  C)
  zero                               done clear
  D)
  infinite done clear
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• question_answer30)
  An inductor of 30 mH is connected to a 220 V, 100 Hz AC source. The inductive reactance is:
  A)
  \[10.58\text{ }\Omega \]                         done clear
  B)
  \[12.64\text{ }\Omega \]  done clear
  C)
  \[18.85\text{ }\Omega \]                         done clear
  D)
  \[22.67\,\,\Omega \] done clear
  View Solution play_arrow

• question_answer31)
  Which of the following graphs represents the correct variation of inductive reactance \[{{X}_{L}}\] with frequency v?
  A)
            done clear
  B)
  done clear
  C)
          done clear
  D)
  done clear
  View Solution play_arrow

• question_answer32)
  What is the resistance offered by a pure inductor for DC?
  A)
  Zero done clear
  B)
  Infinity done clear
  C)
  One done clear
  D)
  Depends on the material done clear
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• question_answer33)
  A 44 mH inductor is connected to 220 V, 50 Hz AC supply. The rms value of the current in the circuit is:
  A)
  12.8 A                           done clear
  B)
  13.6 A    done clear
  C)
  15.9A                            done clear
  D)
  19.5 A done clear
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• question_answer34)
  The reactance of a coil is \[100\,\Omega \]. when used with an AC 240V - 100 Hz supply. The inductance of the coil is:
  A)
  0.16 H                          done clear
  B)
  0.22 H done clear
  C)
  1.6 H                            done clear
  D)
  2.2 H      done clear
  View Solution play_arrow

• question_answer35)
  In a circuit, the current lags behind the voltage by a phase difference of \[\pi /2\]. The circuit contains:
  A)
  only R                           done clear
  B)
  only C done clear
  C)
  only L                           done clear
  D)
  R and C done clear
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• question_answer36)
  In a pure capacitive circuit, if the frequency of AC source is doubled, then its capacitive reactance will be:
  A)
  remains same                 done clear
  B)
  doubled done clear
  C)
  halved              done clear
  D)
  zero done clear
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• question_answer37)
  Which of the following graphs represents the correct variation of capacitive reactance \[{{X}_{C}}\] with frequency v:
  A)
          done clear
  B)
  done clear
  C)
          done clear
  D)
  done clear
  View Solution play_arrow

• question_answer38)
  If a capacitor of \[8\mu F\] is connected to a 220 V, 100 Hz AC source and the current passing through it is 65 mA, then the rms voltage across it is:
  A)
  129.4 V                         done clear
  B)
  12.94 V  done clear
  C)
  1.294 V                         done clear
  D)
  15 V done clear
  View Solution play_arrow

• question_answer39)
  Phase difference between voltage and current in a capacitor in an AC circuit is:
  A)
  \[\pi \]                            done clear
  B)
  \[\pi /2\] done clear
  C)
  0                                  done clear
  D)
  \[\pi /3\] done clear
  View Solution play_arrow

• question_answer40)
  In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?
  A)
  Only resistor          done clear
  B)
  Resistor and inductor done clear
  C)
  Resistor and capacitor done clear
  D)
  Only inductor done clear
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• question_answer41)
  A \[30\text{ }\mu F\] capacitor is connected to a 150V, 60 Hz AC supply. The rms value of current in the circuit is:
  A)
  17 A                             done clear
  B)
  1.7 A done clear
  C)
  1.7 MA                          done clear
  D)
  2.7 A done clear
  View Solution play_arrow

• question_answer42)
  A \[60\,\mu F\] capacitor is connected to a 110 V (rms), 60 Hz AC supply. The rms value of current in the circuit is:
  A)
  1.49 A                           done clear
  B)
  14.9 A    done clear
  C)
  2.49 A                           done clear
  D)
  24.9 A done clear
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• question_answer43)
  An inductor of reactance \[1\,\Omega \] and a resistor of \[2\,\Omega \] are connected in series to the terminals of a 6V (rms) AC source. The power dissipated in the circuit is:
  A)
  8 W                  done clear
  B)
  12 W     done clear
  C)
  14.4 W                          done clear
  D)
  18 W done clear
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• question_answer44)
  In the question number 43, the net power absorbed by the circuit in one complete cycle is:
  A)
  5 W                  done clear
  B)
  10 W    done clear
  C)
  15 W                             done clear
  D)
  zero done clear
  View Solution play_arrow

• question_answer45)
  In which of the following circuits the maximum power dissipation is observed?
  A)
  Pure capacitive circuit done clear
  B)
  Pure inductive circuit done clear
  C)
  Pure resistive circuit   done clear
  D)
  None of these                 done clear
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• question_answer46)
  A capacitor:
  A)
  blocks AC but provides an easy path for DC done clear
  B)
  blocks DC but provides an easy path for AC done clear
  C)
  blocks both AC and DC done clear
  D)
  offers easy path for AC and DC done clear
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• question_answer47)
  The rectance of a capacitor of capacitance C. is X. If both the frequency and capacitance are doubled, the new reactance will be:
  A)
  X                      done clear
  B)
  2 X      done clear
  C)
  4 X                               done clear
  D)
  X/4 done clear
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• question_answer48)
  What is the resistance offered by a capacitor for the steady current?
  A)
  One done clear
  B)
  Zero done clear
  C)
  Infinity done clear
  D)
  Depends on the voltage value done clear
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• question_answer49)
  When an AC is connected to a capacitor what happens?
  A)
  Voltage is leading the current by \[90{}^\circ \] done clear
  B)
  Voltage and current are in phase with each other done clear
  C)
  Voltage and current are out of phase done clear
  D)
  Current leads the voltage by \[90{}^\circ \] done clear
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• question_answer50)
  Which can not allow AC to pass through?
  A)
  resistor                           done clear
  B)
  inductor done clear
  C)
  capacitor                       done clear
  D)
  transistor done clear
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• question_answer51)
  A capacitor of capacitance C has reactance X. If capacitance and frequency become double, then the capacitive reactance will be:
  A)
  2 X                   done clear
  B)
  4 X     done clear
  C)
  \[\frac{X}{2}\]                           done clear
  D)
  \[\frac{X}{4}\] done clear
  View Solution play_arrow

• question_answer52)
  When AC voltage of 220 V is applied to the capacitor C, then:
  A)
  the maximum voltage between plates is 220 V done clear
  B)
  the current is in phase with the applied voltage done clear
  C)
  the charge on the plate is not in phase with the applied voltage done clear
  D)
  power delivered to the capacitor per cycle is zero done clear
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• question_answer53)
  In the circuit shown in figure, what will be the reading of the voltmeter?
  A)
  300 V                done clear
  B)
  900 V done clear
  C)
  200 V                done clear
  D)
  400 V done clear
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• question_answer54)
  In the series LCR circuit shown, the impedance is:
  A)
  \[200\,\Omega \] done clear
  B)
  \[100\,\Omega \] done clear
  C)
  \[300\,\Omega \]             done clear
  D)
  \[500\,\Omega \] done clear
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• question_answer55)
  A circuit containing a \[20\,\Omega \] resistor and \[0.1\text{ }\mu F\]capacitor in series is connected to 230V AC supply of angular frequency \[100\text{ }rad\text{ }{{s}^{-1}}\]. The impedance of the circuit is:
  A)
  \[{{10}^{5}}\Omega \]                         done clear
  B)
  \[{{10}^{4}}\Omega \] done clear
  C)
  \[{{10}^{6}}\Omega \]             done clear
  D)
  \[{{10}^{10}}\Omega \] done clear
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• question_answer56)
  A \[0.2\text{ }k\,\Omega \] resistor and \[15\text{ }\mu \text{F}\] capacitor are connected in series to a 220 V, 50 Hz source. The impedance of the circuit is:
  A)
  \[250\,\Omega \]             done clear
  B)
  \[268\,\Omega \] done clear
  C)
  \[29.15\,\Omega \]                      done clear
  D)
  \[291.5\,\Omega \] done clear
  View Solution play_arrow

• question_answer57)
  A circuit consists of a resistance of \[10\text{ }\Omega \], and a capacitance of 0.1 up. If an alternating emf of 100V, 50 Hz is applied, the current in the circuit is:
  A)
  3.14m A                        done clear
  B)
  6.28 mA done clear
  C)
  1.51mA                         done clear
  D)
  7.36 mA done clear
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• question_answer58)
  200 V AC source is fed to series LCR circuit having \[{{X}_{L}}=50\,\Omega ,\,{{X}_{C}}=50\,\Omega \] and \[R=25\,\Omega \]. Potential drop across the inductor is:
  A)
  100 V                            done clear
  B)
  200 V   done clear
  C)
  400 V                            done clear
  D)
  10 V done clear
  View Solution play_arrow

• question_answer59)
  In series R-L-C circuit, quality factor can be improved by:
  A)
  decreasing L                   done clear
  B)
  increasing C done clear
  C)
  decreasing R                   done clear
  D)
  increasing R and L done clear
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• question_answer60)
  When AC source is connected across series R-L- combination, maximum power loss will occur provided:
  A)
  current and voltage are in phase done clear
  B)
  current from source is minimum done clear
  C)
  inductance is minimum done clear
  D)
  capacitance is maximum done clear
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• question_answer61)
  In R-L-C series AC circuit, impedance cannot be increased by:
  A)
  increasing frequency of source done clear
  B)
  decreasing frequency of source done clear
  C)
  increasing the resistance done clear
  D)
  increasing the voltage of the source   done clear
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• question_answer62)
  A \[100\text{ }\mu \text{F}\] capacitor is in series with a \[40\,\Omega \]. resistor, connected to a 100V, 60Hz supply. The time lag between the current maximum and the voltage maximum is:
  A)
  15.5 ms                         done clear
  B)
  155 ms done clear
  C)
  1.55 ms                         done clear
  D)
  1.55 s done clear
  View Solution play_arrow

• question_answer63)
  In series LCR circuit, the phase angle between supply voltage and current is:
  A)
  \[\tan \,\phi =\frac{{{X}_{L}}-{{X}_{C}}}{R}\] done clear
  B)
  \[\tan \,\phi =\frac{R}{{{X}_{L}}-{{X}_{C}}}\] done clear
  C)
  \[\tan \,\phi =\frac{R}{{{X}_{L}}+{{X}_{C}}}\]           done clear
  D)
  \[\tan \,\phi =\frac{{{X}_{L}}+{{X}_{C}}}{R}\] done clear
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• question_answer64)
  An LCR circuit is predominantly capacitive if:
  A)
  \[{{X}_{L}}>{{X}_{C}}\]        done clear
  B)
              \[{{X}_{L}}<{{X}_{C}}\] done clear
  C)
  \[{{X}_{L}}={{X}_{C}}\]                    done clear
  D)
  None of these done clear
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• question_answer65)
  To reduce the resonant frequency in an LCR series circuit with a generator:            (NCERT EXEMPLAR)
  A)
  the generator frequency should be reduced done clear
  B)
  another capacitor should be added in parallel to the first done clear
  C)
  the iron core of the inductor should be removed done clear
  D)
  dielectric in the capacitor should be removed done clear
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• question_answer66)
  When an AC voltage is applied to a L-C-R circuit, which of the following is true?
  A)
  l and V are out of phase with each other in R done clear
  B)
  l and V are in phase in L with in C, they are out of phase done clear
  C)
  l and V are out of phase in both, C and L done clear
  D)
  l and V are out of phase in L and in phase in C done clear
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• question_answer67)
  An LCR series AC circuit is at resonance with 10 V each across L, C and R. If the resistance is halved, the respective voltages across L, C and R are:
  A)
  10, V, 10 V and 5 V   done clear
  B)
  10 V, 10 V and 10 V  done clear
  C)
  20 V, 20 V and 5 V    done clear
  D)
  20 V, 20 V and 10 V done clear
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• question_answer68)
  In a series LCR circuit the voltage across an inductor, capacitor and resistor are 20 V, 20 V and 40 V respectively. The phase difference between the applied voltage and the current in the circuit is:
  A)
  \[30{}^\circ \]                           done clear
  B)
  \[45{}^\circ \] done clear
  C)
  \[60{}^\circ \]                           done clear
  D)
  \[0{}^\circ \] done clear
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• question_answer69)
  When an AC source of voltage \[V={{V}_{0}}\sin \,100t\] is connected across a circuit, the phase difference between the voltage V and current l in the circuit is observed to be \[\pi /4\]. as shown in figure. If the circuit consists possibly only of RC or RL or LC in series, find possible values of two elements.
  A)
  \[R=1k\Omega ,\,C=10\,\mu F\]  done clear
  B)
  \[R=1k\Omega ,\,C=1\,\mu F\] done clear
  C)
  \[R=1k\Omega ,\,L=1\,0\,mH\]    done clear
  D)
  \[R=10k\Omega ,\,L=1\,0\,mH\] done clear
  View Solution play_arrow

• question_answer70)
  In a circuit, L, C and R are connected in series with an alternating voltage source of frequency v. The current leads the voltage by \[45{}^\circ \]. The value of C is:
  A)
  \[\frac{1}{\pi v(2\pi vL-R)}\]        done clear
  B)
  \[\frac{1}{2\pi v(2\pi vL-R)}\] done clear
  C)
  \[\frac{1}{\pi v(2\pi vL+R)}\]      done clear
  D)
  \[\frac{1}{2\pi v(2\pi vL+R)}\] done clear
  View Solution play_arrow

• question_answer71)
  At resonance frequency the impedance in series LCR circuit is:
  A)
  maximum                      done clear
  B)
  minimum done clear
  C)
  zero                   done clear
  D)
  infinity done clear
  View Solution play_arrow

• question_answer72)
  An LCR series circuit is under resonance. If \[{{l}_{m}}\] is current amplitude, \[{{V}_{m}}\] is voltage amplitude, R is the resistance, Z is the impedance, \[{{X}_{L}}\] is the inductive reactance and \[{{X}_{C}}\] is the capacitive reactance, then:
  A)
  \[{{l}_{m}}=\frac{Z}{{{V}_{m}}}\]                 done clear
  B)
  \[{{l}_{m}}=\frac{{{V}_{m}}}{{{X}_{L}}}\] done clear
  C)
  \[{{l}_{m}}=\frac{{{V}_{m}}}{{{X}_{C}}}\]              done clear
  D)
  \[{{l}_{m}}=\frac{{{V}_{m}}}{R}\] done clear
  View Solution play_arrow

• question_answer73)
  At resonant frequency the current amplitude in series LCR circuit is:
  A)
  maximum                      done clear
  B)
  minimum done clear
  C)
  zero                               done clear
  D)
  infinity done clear
  View Solution play_arrow

• question_answer74)
  The resonant frequency of a series LCR circuit with \[L=2.0\,\,H,C=32\mu F\] and \[R=10\,\Omega \]is:
  A)
  20 Hz                            done clear
  B)
  30 Hz   done clear
  C)
  40 Hz                            done clear
  D)
   50 Hz done clear
  View Solution play_arrow

• question_answer75)
  Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?                                                                                              (NCERT EXEMPLAR)
  A)
  \[R=20\Omega ,\,\,L=1.5\,H,C=35\mu F\] done clear
  B)
  \[R=25\Omega ,\,\,L=2.5\,\,H,C=45\mu F\] done clear
  C)
  \[R=15\Omega ,\,\,L=3.5\,\,H,C=30\mu F\] done clear
  D)
  \[R=25\Omega ,\,\,L=1.5\,\,H,C=45\mu F\] done clear
  View Solution play_arrow

• question_answer76)
      The Q factor of a series LCR circuit with \[L=2\,H,\,C=32\,\mu F\] and \[R=10\,\Omega \] is:
  A)
  15                     done clear
  B)
  20      done clear
  C)
  25                     done clear
  D)
  30 done clear
  View Solution play_arrow

• question_answer77)
  In a series LCR circuit, resistance, voltage and frequency of the main supply is \[200\text{ }\Omega ,\text{ }220\text{ }V\]and 50 Hz respectively. If capacitor is taken out from the circuit, the current lags behind the voltage by \[30{}^\circ \]. If inductor is taken out from the circuit, the current leads the voltage by \[30{}^\circ \]. The power dissipated in LCR-circuit is:
  A)
  zero                   done clear
  B)
  210 W   done clear
  C)
  242 W                           done clear
  D)
  305 W done clear
  View Solution play_arrow

• question_answer78)
  A series LCR circuit with \[C=10\mu F\] and \[\omega =1000\text{ }rad/s\], has maximum current flowing through it. The value of inductance will be:
  A)
  100 mH done clear
  B)
  10 mH done clear
  C)
  1 mH  done clear
  D)
  cannot be calculated, unless R is known done clear
  View Solution play_arrow

• question_answer79)
  In a series LCR circuit at resonance, the circuit is purely:
  A)
  resistive done clear
  B)
  inductive done clear
  C)
  capacitive done clear
  D)
  either capacitive or inductive done clear
  View Solution play_arrow

• question_answer80)
  In a LCR circuit the net reactance is equal to ohmic resistance. What is the phase difference between current and voltage?
  A)
  \[0{}^\circ \]                             done clear
  B)
  \[45{}^\circ \]      done clear
  C)
  \[90{}^\circ \]                           done clear
  D)
  \[30{}^\circ \] done clear
  View Solution play_arrow

• question_answer81)
  Find the impedance of a series LCR circuit if the inductive reactance, capacitive reactance and resistance are \[6\,\Omega ,\text{ }3\Omega \] and \[4\,\Omega \] respectively. Calculate the impedance of the circuit.
  A)
  \[5\,\Omega \]                            done clear
  B)
  \[25\,\Omega \]    done clear
  C)
  \[0\,\Omega \]                            done clear
  D)
  \[13\,\Omega \] done clear
  View Solution play_arrow

• question_answer82)
  At resonance in LCR circuit what happens to the impedance?
  A)
  becomes zero       done clear
  B)
  becomes ohmic resistance done clear
  C)
  becomes high        done clear
  D)
  becomes infinity done clear
  View Solution play_arrow

• question_answer83)
  Figure shows a series LCR circuit connected to a variable frequency 230 V source. The source frequency which drives the circuit in resonance is:
  A)
  4 Hz     done clear
  B)
              5 Hz    done clear
  C)
  6 Hz                              done clear
  D)
  8 Hz done clear
  View Solution play_arrow

• question_answer84)
  In LCR-circuit if resistance increases, quality factor:
  A)
  increases finitely              done clear
  B)
  decreases finitely done clear
  C)
  remains constant             done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer85)
  In a series LCR circuit having \[L=30\text{ }mH,\text{ }R=8\,\Omega .\] and the resonant frequency is 50 Hz. The quality factor of the circuit is:
  A)
  0.118                            done clear
  B)
  11.8      done clear
  C)
  118                               done clear
  D)
  1.18 done clear
  View Solution play_arrow

• question_answer86)
  A series resonant LCR circuit has a quality factor (Q-factor) \[=0.4.\text{ }I\text{f }R=2\text{ k}\,\Omega ,\text{ }C=0.1\,\mu F\], then the value of inductance is:
  A)
  0.1 H                            done clear
  B)
  0.064 H done clear
  C)
  2 H                               done clear
  D)
  5 H done clear
  View Solution play_arrow

• question_answer87)
  In a series LCR circuit, the plot of \[{{l}_{m}}vs\,\,\omega \]is shown in the figure. The bandwidth of this plot will be:
  A)
  zero                               done clear
  B)
  \[0.1\,rad\,{{s}^{-1}}\] done clear
  C)
  \[0.2\,rad\,{{s}^{-2}}\]             done clear
  D)
  \[0.4\,rad\,{{s}^{-1}}\] done clear
  View Solution play_arrow

• question_answer88)
  A series LCR circuit with \[R=20\text{ }\Omega .,\text{ }L=1.5\text{ }H\]and \[C=35\mu F\,\]is connected to a variable frequency 200 V AC supply. When the frequency of the supply equals the natural frequency of the circuit, the average power transferred to the circuit in one complete cycle is:
  A)
  200 W                           done clear
  B)
  2000 W done clear
  C)
  100 W                           done clear
  D)
  4000 W done clear
  View Solution play_arrow

• question_answer89)
  The equations of instantaneous voltage and current are given as \[v=100\text{ }sin\text{ }314t\] and \[i=100\,\sin \,(314t+60{}^\circ )\] What is the power factor of the circuit?
  A)
  5000 W             done clear
  B)
  10000 W done clear
  C)
  0 W                  done clear
  D)
  2500 W done clear
  View Solution play_arrow

• question_answer90)
  A series LCR circuit with \[R=22\,\Omega ,L=1.5\,H\]and \[C=40\mu F\] is connected to a variable frequency 220 V AC supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?
  A)
  2000 W                         done clear
  B)
  2200 W done clear
  C)
  2400 W                         done clear
  D)
  2500 W done clear
  View Solution play_arrow

• question_answer91)
  An alternating supply of 220 V is applied across a circuit with resistance \[22\text{ }\Omega \] and impedance \[\text{44 }\Omega \]. The power dissipated in the circuit is:
  A)
  1100 W                         done clear
  B)
  550W done clear
  C)
  2200 W            done clear
  D)
  (2200/3) W done clear
  View Solution play_arrow

• question_answer92)
  An alternating current generator has an internal resistance \[{{R}_{g}}\] and an internal reactance \[{{X}_{g}}\]. It is used to supply power to a passive Load consisting of a resistance \[{{R}_{g}}\] and a reactance \[{{X}_{L}}\]. For maximum power to be delivered from the generator to the load, the value of \[{{X}_{L}}\] is equal to: (NCERT EXEMPLAR)
  A)
  zero                   done clear
  B)
  \[{{X}_{g}}\]      done clear
  C)
  \[-{{X}_{g}}\]                           done clear
  D)
  \[{{R}_{g}}\] done clear
  View Solution play_arrow

• question_answer93)
  For an LCR circuit, the power transferred from the driving source to the driven oscillator is \[P={{l}^{2}}Z\,\cos \,\phi \]. Then:
  A)
  the power factor \[\cos \,\phi \ge 0,\,P\ge 0\] done clear
  B)
  the driving force can give no energy to the oscillator (P = 0) in some cases done clear
  C)
  the driving force cannot siphon out(P < 0)the energy out of oscillator done clear
  D)
  All of the above done clear
  View Solution play_arrow

• question_answer94)
  A voltage of peak value 283 V and varying frequency is applied to series LCR combination in which \[R=3\,\,\Omega ,\,\,L=25\,mH\] and\[C=400\mu F\]. Then the frequency (in Hz) of the source at which maximum power is dissipated in the above is:
  A)
  51.5                              done clear
  B)
  50.7     done clear
  C)
  51.1                              done clear
  D)
  50.3 done clear
  View Solution play_arrow

• question_answer95)
  The natural frequency \[({{\omega }_{0}})\] of oscillations in LC circuit is given by:
  A)
  \[\frac{1}{2\pi }\frac{1}{\sqrt{LC}}\]                  done clear
  B)
  \[\frac{1}{\pi }\frac{1}{\sqrt{2LC}}\] done clear
  C)
  \[\frac{1}{\sqrt{LC}}\]               done clear
  D)
  \[\sqrt{LC}\] done clear
  View Solution play_arrow

• question_answer96)
  What is the analogy of force constant in electrical system?
  A)
  capacitance           done clear
  B)
  reciprocal of capacitance done clear
  C)
  inductance            done clear
  D)
  reciprocal of inductance done clear
  View Solution play_arrow

• question_answer97)
  A charged \[30\,\mu F\] capacitor is connected to a 27 mH inductor. The angular frequency of free oscillations of the circuit is:
  A)
  \[1.1\times {{10}^{3}}rad\text{ }{{s}^{-1}}\]              done clear
  B)
  \[2.1\times {{10}^{3}}\text{ }rad\text{ }{{s}^{-1}}\] done clear
  C)
  \[3.1\times {{10}^{3}}rad\text{ }{{s}^{-1}}\]      done clear
  D)
  \[4.1\times {{10}^{3}}rad\text{ }{{s}^{-1}}\] done clear
  View Solution play_arrow

• question_answer98)
  An LC circuit contains a 20 mH inductor and a \[50\text{ }\mu F\] capacitor with an initial charge of 10 mC. The resistance of the circuit is negligible. Let the instant at which the circuit which is closed be \[t=0\]. At what time the energy stored is completely magnetic?
  A)
  1 = 0                done clear
  B)
  t = 1.57 ms done clear
  C)
  t = 3.14 ms                   done clear
  D)
  t = 6.28 ms done clear
  View Solution play_arrow

• question_answer99)
  An LC circuit contains a 20 mH inductor and a \[25\text{ }\mu \text{F}\] capacitor with an initial charge of 5 mC. The total energy stored in the circuit initially is:
  A)
  5 J                    done clear
  B)
  0.5 J    done clear
  C)
  50 J                              done clear
  D)
  500 J done clear
  View Solution play_arrow

• question_answer100)
  An LC-circuit contains 10 mH inductor and 25 mF capacitor with given initial charge. The resistance of the circuit is negligible. The energy stored in circuit is completely magnetic at time (in millisecond) the time is measured from the instant when the circuit is closed:
  A)
  \[0,\frac{\pi }{2},\frac{2\pi }{2},...etc\]    done clear
  B)
  \[\frac{\pi }{3},\frac{2\pi }{3},\frac{5\pi }{3},...etc.\] done clear
  C)
  \[\frac{\pi }{4},\frac{3\pi }{4},\frac{5\pi }{5},...etc\]        done clear
  D)
  \[0,\frac{\pi }{8},\frac{\pi }{4},...etc.\] done clear
  View Solution play_arrow

• question_answer101)
  What is the mechanical equivalent of spring constant k in LC oscillating circuit?
  A)
  \[\frac{1}{L}\]                           done clear
  B)
  \[\frac{1}{C}\] done clear
  C)
  \[\frac{L}{C}\]                           done clear
  D)
  \[\frac{1}{LC}\] done clear
  View Solution play_arrow

• question_answer102)
  In an ideal LC-circuit, the capacitor is charged by connecting it to a DC source, which is then disconnected. The current in the circuit:
  A)
  becomes zero instantaneously done clear
  B)
  grows monotonically done clear
  C)
  decays monotonically done clear
  D)
  oscillates instantaneously done clear
  View Solution play_arrow

• question_answer103)
  A transformer works on the principle of:
  A)
  self induction done clear
  B)
  electrical inertia done clear
  C)
  mutual induction done clear
  D)
  magnetic effect of the electrical current done clear
  View Solution play_arrow

• question_answer104)
    Transformer is used to:
  A)
  convert AC to DC voltage done clear
  B)
  convert DC to AC voltage done clear
  C)
  obtain desired DC power done clear
  D)
  obtain desired AC voltage and current done clear
  View Solution play_arrow

• question_answer105)
  For an ideal step-down transformer, the quantity which is constant for both the coils is:
  A)
  current in the coils    done clear
  B)
  voltage across the coils done clear
  C)
  resistance of coils     done clear
  D)
  power in the coils done clear
  View Solution play_arrow

• question_answer106)
  High voltage transmission line is preferred, as:
  A)
  its appliances are less costly done clear
  B)
  thin power cables are required done clear
  C)
  idle current very low done clear
  D)
  (d) power loss is very less done clear
  View Solution play_arrow

• question_answer107)
  In a transformer, the no. of turns of primary and secondary coils are 500 and 400 respectively. If 220 V is supplied to the primary coil, then ratio of currents in primary and secondary coils is:
  A)
  4:5                    done clear
  B)
  5:4    done clear
  C)
  5:9                    done clear
  D)
  9:5 done clear
  View Solution play_arrow

• question_answer108)
  Quantity that remains unchanged in a transformer is:
  A)
  voltage                          done clear
  B)
  current done clear
  C)
  frequency                       done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer109)
  The core of a transformer is Laminated to reduce:
  A)
  flux leakage                    done clear
  B)
  hysteresis done clear
  C)
  copper loss                     done clear
  D)
  eddy current done clear
  View Solution play_arrow

• question_answer110)
  The loss of energy in the form of heat in the iron core of a transformer is:
  A)
  iron loss                         done clear
  B)
  copper loss                 done clear
  C)
    mechanical loss              done clear
  D)
  None of these                 done clear
  View Solution play_arrow

• question_answer111)
  The output of a step down transformer is measured to be 24 V when connected to a 12W light bulb. The value of the peak current is:                                                                  (NCERT EXEMPLAR)
  A)
  \[\frac{1}{\sqrt{2}}A\]                done clear
  B)
  \[\sqrt{2}\,A\] done clear
  C)
  \[2\,A\]                          done clear
  D)
  \[2\,\sqrt{2}\,A\] done clear
  View Solution play_arrow

• question_answer112)
  In a transformer the transformation ratio is 0.3. If 220 VAC is fed to the primary, then the voltage across the secondary is:
  A)
  44 V                 done clear
  B)
  55 V    done clear
  C)
  60 V                             done clear
  D)
  66 V   done clear
  View Solution play_arrow

• question_answer113)
  The ratio of number of turns of primary coil to secondary coil in a transformer is 2 : 3. If a cell of 6 V is connected across the primary coil. then voltage across the secondary coil will be:
  A)
  3 V                               done clear
  B)
  6 V      done clear
  C)
  9 V                               done clear
  D)
  12 V done clear
  View Solution play_arrow

• question_answer114)
  A transformer is used to light 140 W, 24 V lamp from a 240V AC mains. If the main current is 0.7 A, the efficiency of the transformer is:
  A)
  63.8%                           done clear
  B)
  74%    done clear
  C)
  83.3%                           done clear
  D)
  48% done clear
  View Solution play_arrow

• question_answer115)
  In a step up transformer the turn ratio is 1:2. A Leclanche cell (emf = 1.5 V) is connected across the primary. The voltage across the secondary is:
  A)
  3 V                               done clear
  B)
  1.5 V     done clear
  C)
  0.75 V                           done clear
  D)
  zero done clear
  View Solution play_arrow

• question_answer116)
  A transformer has primary and secondary winding as 2000 and 200 respectively. It is connected to a Lechlanche cell of 1.5V. What is the output voltage of the transformer?
  A)
  0.15 V                           done clear
  B)
  1.5 V     done clear
  C)
  0.1 V                            done clear
  D)
  0 V done clear
  View Solution play_arrow

• question_answer117)
  A transformer has 100 turns in the primary coil and carries 8 A current. If input power is 1 kW, the number of turns in secondary coil to have 500 V output will be:
  A)
  100                   done clear
  B)
  200    done clear
  C)
  400                               done clear
  D)
  300 done clear
  View Solution play_arrow

• question_answer118)
  A 60 W load is connected to the secondary of an ideal transformer whose primary draws line voltage. If a current of 0.54 A flows in the load, the current in the primary coil is:
  A)
  0.27 mA                        done clear
  B)
  2.7 A     done clear
  C)
  0.27 A                           done clear
  D)
  10 A done clear
  View Solution play_arrow

• question_answer119)
  The turns ratio of a transformer is given as 2 : 3. If the current through the primary coil is 3 A, thus calculate the current through the resistance.
  A)
  1 A                               done clear
  B)
  4.5 A  done clear
  C)
  2 A                               done clear
  D)
  1.5 A             done clear
  View Solution play_arrow

• question_answer120)
  When power is drawn from the secondary coil of the transformer, the dynamic resistance:
  A)
  increases                        done clear
  B)
  decreases done clear
  C)
  remains unchanged         done clear
  D)
  changes erratically done clear
  View Solution play_arrow

• question_answer121)
            A step down transformer converts transmission line voltage from 11000V to 220V. The primary of the transformer has 6000 turns and efficiency of the transformer is 60%. If the output power is 9 kW, then the input power will be:
  A)
  11 kW                           done clear
  B)
  12 kW   done clear
  C)
  14 kW                           done clear
  D)
  15 kW done clear
  View Solution play_arrow

• question_answer122)
  In the question number 121, the number of turns in the secondary is:
  A)
  20                     done clear
  B)
  80      done clear
  C)
  120                               done clear
  D)
  160  done clear
  View Solution play_arrow

• question_answer123)
  A power transmission line feeds input power at 2400V to a step down transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary windings in order to get output power at 240 V?
  A)
  400                   done clear
  B)
  420     done clear
  C)
  424                               done clear
  D)
  436 done clear
  View Solution play_arrow

• question_answer124)
  The current drawn by the primary of a transformer, which step down 200 V to 20 V to operate a device of resistance \[20\,\Omega \] is (Assume the efficiency of the transformer to be 80%):
  A)
  0.125 A done clear
  B)
                          0.225 A done clear
  C)
  0.325 A                         done clear
  D)
  0.425 A done clear
  View Solution play_arrow

• question_answer125)
  The primary and secondary coils of a transformer have 50 and 1500 turns respectively. The magnetic flux linked with the primary coil is given by \[\phi ={{\phi }_{0}}+4t\], where \[{{\phi }_{0}}\] is a constant. The output voltage across the secondary coil is:
  A)
  30 V                 done clear
  B)
  90 V    done clear
  C)
  120 V done clear
  D)
  220 V done clear
  View Solution play_arrow