12th Class Physics Alternating Current / प्रत्यावर्ती धारा Question Bank

done MCQs - Alternating Current Total Questions - 22

• question_answer1)
  If the rms current in a 50 Hz AC circuit is 5 A, the value of the current 1/300 s after its value becomes zero is
  A)
  \[5\sqrt{2}\operatorname{A}\] done clear
  B)
  \[5\sqrt{\frac{3}{2}}\operatorname{A}\] done clear
  C)
  \[\frac{5}{6}\]A done clear
  D)
  \[\frac{5}{\sqrt{2}}\operatorname{A}\] done clear
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• question_answer2)
  An alternating current generator has an internal resistance \[{{R}_{g}}\] and an internal reactance \[{{\operatorname{X}}_{g}}\]. It is used to supply power to a passive load consisting of a resistance \[{{R}_{g}}\], and a reactance \[{{\operatorname{X}}_{\operatorname{L}}}\]. For maximum power to be delivered from the generator to the load, the value of \[{{\operatorname{X}}_{\operatorname{L}}}\] is equal to
  A)
  zero done clear
  B)
  \[{{\operatorname{X}}_{g}}\] done clear
  C)
  -\[{{\operatorname{X}}_{g}}\] done clear
  D)
  \[{{R}_{g}}\] done clear
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• question_answer3)
  When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of 220 V this means
  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_answer4)
  When frequency of applied alternating voltage very high then                                        
  A)
  A capacitor will tend to become SHORT done clear
  B)
  An inductor will tend to become SHORT          done clear
  C)
  Both [a] and [b]                                    done clear
  D)
  No one will become short                   done clear
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• question_answer5)
  Relation between r.m.s. voltage and instantaneous voltage of an AC
  A)
  \[{{\operatorname{V}}_{0}}={{V}_{RMS}}/\surd 2\] done clear
  B)
  \[{{V}_{RMS}}={{\operatorname{V}}_{0}}/\surd 2\]      done clear
  C)
  \[{{V}_{RMS}}=0.707{{\operatorname{V}}_{0}}\] done clear
  D)
  Both [c] and [d]            done clear
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• question_answer6)
  The heat produced in a given resistance in a given time by the sinusoidal current \[{{\operatorname{I}}_{0}}\] sin cot will be the same as heat produced by a steady current of magnitude
  A)
  0.707 \[{{\operatorname{I}}_{0}}\] done clear
  B)
  1.412 \[{{\operatorname{I}}_{0}}\] done clear
  C)
   \[{{\operatorname{I}}_{0}}\] done clear
  D)
  \[\surd {{\operatorname{I}}_{0}}\] done clear
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• question_answer7)
  An A.C. source is connected to a resistive circuit. Which of the following statements is true?         
  A)
  Current leads the voltage in phase done clear
  B)
  Current lags the voltage in phase done clear
  C)
  Current and voltage are in same phase done clear
  D)
  Either [a] or [b] depending on the value of resistance. done clear
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• question_answer8)
  In which of the following circuit power dissipation is maximum?
  A)
  Pure capacitive circuit done clear
  B)
  Pure inductive circuit done clear
  C)
  Pure resistive circuit done clear
  D)
  LR or CR circuit   done clear
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• question_answer9)
  To reduce the resonant frequency in an L-C-R series circuit with a generator
  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_answer10)
  Which of the following combinations should be selected for better tuning of an L-C-R circuit used for communication?
  A)
  \[\operatorname{R}\text{ }=\text{ }20\text{ }\Omega ,\operatorname{L}\text{ }=\text{ }1.5\text{ }\operatorname{H}, C\text{ }=\text{ }35\text{ }\mu \operatorname{F}\] done clear
  B)
  \[\operatorname{R}\text{ }=\text{ }25\text{ }\Omega ,\operatorname{L}\text{ }=\text{ 2}.5\text{ }\operatorname{H}, C\text{ }=\text{ 4}5\text{ }\mu \operatorname{F}\] done clear
  C)
  \[\operatorname{R}\text{ }=\text{ 1}5\text{ }\Omega ,\operatorname{L}\text{ }=\text{ 3}.5\text{ }\operatorname{H}, C\text{ }=\text{ 30 }\mu \operatorname{F}\] done clear
  D)
  \[\operatorname{R}\text{ }=\text{ 2}5\text{ }\Omega ,\operatorname{L}\text{ }=\text{ 1}.5\text{ }\operatorname{H}, C\text{ }=\text{ 45 }\mu \operatorname{F}\]   done clear
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• question_answer11)
  With increase in frequency of an A.C. supply, the impedance of a series L-C-R circuit
  A)
  remains constant. done clear
  B)
  increases. done clear
  C)
  decreases. done clear
  D)
  decreases at first, becomes minimum and then increases. done clear
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• question_answer12)
  The sharpness of tuning of a series LCR circuit at resonance is measured by Q factor of the circuit which is given by
  A)
   \[\operatorname{Q}=\frac{1}{R}\sqrt{\frac{L}{C}}\] done clear
  B)
  \[\operatorname{Q}=\frac{1}{R}\sqrt{\frac{C}{L}}\] done clear
  C)
   \[\operatorname{Q}=\frac{1}{L}\sqrt{\frac{R}{\operatorname{C}}}\] done clear
  D)
  \[\operatorname{Q}=\frac{1}{C}\sqrt{\frac{R}{L}}\] done clear
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• question_answer13)
  At resonance, the impedance in series LCR circuit is
  A)
  maximum. done clear
  B)
  zero. done clear
  C)
  infinity. done clear
  D)
  minimum. done clear
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• question_answer14)
  The power factor of series LCR circuit at resonance is
  A)
  0.707 done clear
  B)
  1 done clear
  C)
  0.5 done clear
  D)
  0 done clear
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• question_answer15)
  When a capacitor C is charged to a certain potential and connected to an inductor L, then frequency of energy oscillation is given by
  A)
  \[\frac{1}{2\pi \sqrt{\operatorname{LC}}}\] done clear
  B)
  \[\frac{1}{\sqrt{\operatorname{LC}}}\] done clear
  C)
   \[\frac{2\pi }{\sqrt{\operatorname{LC}}}\] done clear
  D)
  \[\frac{1}{2\pi }\sqrt{\frac{L}{C}}\] done clear
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• question_answer16)
  The output of a step-down transformer is measured to be 24 V when connected to a 12 W Light bulb. The value of the peak current is
  A)
  1/\[\sqrt{2}\]A done clear
  B)
  \[\sqrt{2}\] A done clear
  C)
  2 A done clear
  D)
  2\[\sqrt{2}\]A done clear
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• question_answer17)
  The underlying principle of transformer is
  A)
  resonance. done clear
  B)
  mutual induction. done clear
  C)
  self induction. done clear
  D)
  none of the above. done clear
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• question_answer18)
  The core of a transformer is laminated as
  A)
  it improves the ratio of voltage in the primary and secondary may be increased. done clear
  B)
  it checks rusting of the core may be stopped. done clear
  C)
  it reduces energy losses due to eddy currents. done clear
  D)
  it increases flux linkage. done clear
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• question_answer19)
  If rotational velocity of an armature is doubled, emf generated in a generator will be
  A)
  half. done clear
  B)
  two times. done clear
  C)
  four times. done clear
  D)
  unchanged. done clear
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• question_answer20)
  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
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• question_answer21)
  ______ increases in step-down transformer.
  A)
  Voltage done clear
  B)
  Current done clear
  C)
  Power done clear
  D)
  Current density   done clear
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• question_answer22)
  The efficiency of transformer is very high because
  A)
  There is no moving part done clear
  B)
  It uses AC only done clear
  C)
  It uses the copper wire for the coils done clear
  D)
  None of the above done clear
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