12th Class Physics Electro Magnetic Induction Question Bank

done MCQs - Electromagnetic Induction Total Questions - 16

• question_answer1)
  A square of side L meters lies in the x-y plane in a region where the magnetic field is given by \[\operatorname{B}={{B}_{0}}\text{ (}2\hat{i}+3\hat{j}+4\hat{k})\] Testa, where \[{{B}_{0}}\] is constant. The magnitude of flux passing through the square is
  A)
  \[2{{B}_{0}}{{\text{L}}^{2}}\text{Wb}\] done clear
  B)
  \[3{{B}_{0}}{{\text{L}}^{2}}\text{Wb}\] done clear
  C)
  \[4{{B}_{0}}{{\text{L}}^{2}}\text{Wb}\] done clear
  D)
  \[\sqrt{29}{{B}_{0}}{{\text{L}}^{2}}\text{Wb}\] done clear
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• question_answer2)
  A loop, made of straight edges has six corners at A (0, 0, 0), B (L, 0, 0) C (L, L, 0), D (0, L,0), E (0, L, L) and F (0,0, L). A magnetic field B= \[{{B}_{0}}\text{ }(\hat{i}+\hat{k})\] Testa is present in the region. The flux passing through the loop ABCDEFA (in that order) is
  A)
  \[{{B}_{0}}{{L}^{2}}Wb\]. done clear
  B)
  2\[{{B}_{0}}{{L}^{2}}Wb\]. done clear
  C)
  \[\sqrt{2}{{B}_{0}}{{L}^{2}}Wb\]. done clear
  D)
  \[4{{B}_{0}}{{L}^{2}}Wb\] . done clear
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• question_answer3)

  A cylindrical bar magnet is rotated about its axis in the figure. A wire is connected from the axis and is made to touch the cylindrical surface through a contact. Then

  A)
  a direct current flows in the ammeter A. done clear
  B)
  no current flows through the ammeter A. done clear
  C)
  an alternating sinusoidal current flows through the ammeter A with a time period \[2\pi /\omega \] done clear
  D)
  a time varying non-sinusoidal current flows through the ammeter A. done clear
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• question_answer4)

  There are two coils A and B as shown in figure. A current starts flowing in B as shown, when A is moved towards B and stops when A stops moving. The current in A is counter clockwise. B is kept stationary when A moves. We can infer that

  A)
  there is a constant current in the clockwise direction in A. done clear
  B)
  there is a varying current in A. done clear
  C)
  there is no current in A. done clear
  D)
  there is a constant current in the counter clockwise direction in A. done clear
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• question_answer5)

  Same as problem 4 except the coil A is made to rotate about a vertical axis figure. No current flows in B if A is at rest. The current in coil A, when the current in B (at t = 0) is counter-clockwise and the coil A is as shown at this instant, t = 0, is

   
  A)
  constant current clockwise. done clear
  B)
  varying current clockwise. done clear
  C)
  varying current counter-clockwise. done clear
  D)
  constant current counter-clockwise. done clear
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• question_answer6)
  The polarity of induced emf is defined by
  A)
  Ampere's circuital law. done clear
  B)
  Biot-Savart law. done clear
  C)
  Lenz's law. done clear
  D)
  Fleming's right hand rule. done clear
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• question_answer7)
  Lenz's law is consequence of the law of conservation of
  A)
  Charge done clear
  B)
  mass done clear
  C)
  energy done clear
  D)
  momentum done clear
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• question_answer8)
  The magnetic flux linked with a coil is given by an equation \[\phi =5{{t}^{2}}+2t+3\]. The induced e.m.f. in the coil at the third second will be
  A)
  32 units done clear
  B)
  54 units done clear
  C)
  40 units done clear
  D)
  65 units done clear
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• question_answer9)
  The self-inductance L of a solenoid of length I and  area of cross-section A, with a fixed number of turns N increases as
  A)
  I and A increase. done clear
  B)
  I decreases and A increases. done clear
  C)
  I increases and A decreases. done clear
  D)
  both I and A decrease. done clear
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• question_answer10)
  An iron-cored solenoid has self-inductance 2.8H. When the core is removed, the self-inductance becomes 2 mH. The relative permeability of the material of the core is
  A)
  1400 done clear
  B)
  1200 done clear
  C)
  2800 done clear
  D)
  2000 done clear
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• question_answer11)
  In which of the following application, eddy current has no role to play?
  A)
  Electric power meters done clear
  B)
  Induction furnace done clear
  C)
  LED lights done clear
  D)
  Magnetic brakes in trains done clear
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• question_answer12)
  Which one of the following statements is wrong?
  A)
  Eddy currents are produced in a steady magnetic field. done clear
  B)
  Eddy current is used to produce braking force done clear
  C)
  Eddy currents is minimized by using l aminated core. done clear
  D)
  Induction furnace uses eddy current to produce heat done clear
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• question_answer13)
  If the back e.m.f. induced in a coil, when current changes from 1A to zero in one millisecond, is 5 volts, the self-inductance of the coil is
  A)
  5 H done clear
  B)
  1 H done clear
  C)
  5\[\times {{10}^{-3}}\operatorname{H}\] done clear
  D)
  5\[\times {{10}^{3}}\operatorname{H}\] done clear
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• question_answer14)
  Magnetic field energy stored in a coil is
  A)
  \[{{\operatorname{Li}}^{2}}\] done clear
  B)
  \[\frac{1}{2}\operatorname{Li}\] done clear
  C)
  \[\operatorname{Li}\] done clear
  D)
  \[\frac{1}{2}{{\operatorname{Li}}^{2}}\] done clear
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• question_answer15)
  If two coils of self inductance \[{{\operatorname{L}}_{1}}\] and \[{{\operatorname{L}}_{2}}\] are coupled together, their mutual inductance becomes
  A)
  \[\operatorname{M}=k\sqrt{{{\operatorname{L}}_{1}}{{L}_{2}}}\] done clear
  B)
  \[\operatorname{M}=k\sqrt{\frac{{{L}_{1}}}{{{L}_{2}}}}\] done clear
  C)
  \[\operatorname{M}=k\sqrt{{{\operatorname{L}}_{1}}+{{L}_{2}}}\] done clear
  D)
  None of the above done clear
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• question_answer16)
  An inductor and a bulb are connected in series with a dc source. A soft iron core is then inserted in the inductor. What will happen to intensity of the bulb?
  A)
  Intensity of the bulb remains the same. done clear
  B)
  Intensity of the bulb decreases. done clear
  C)
  Intensity of the bulb increases done clear
  D)
  The bulb ceases to glow. done clear
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