12th Class Physics Electro Magnetic Induction Question Bank

done Case Based (MCQs) - Electromagnetic Induction Total Questions - 30

• question_answer1)

  Directions : (1-5)

  Direction of Induced Current

  Lenz's law states that the direction of induced current in a circuit is such that it opposes the change which produces it. Thus, if the magnetic flux linked with a closed circuit increases, the induced current flows in such a direction that a magnetic flux is created in the opposite direction of the original magnetic flux. If the magnetic flux linked with the closed circuit decreases, the induced current flow in such a direction so as to create a magnetic flux in the direction of the original flux.

  Which of the following statements is correct?
  A)
  The induced e.m.f. is not in the direction opposing the change in magnetic flux so as to oppose the cause which prodocues it. done clear
  B)
  The relative motion between the coil and magnet produces change in magnetic flux. done clear
  C)
  Emf is induced only if the magnet is moved towards coil done clear
  D)
  Emf is induced only if the coil is moved towards magnet. done clear
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• question_answer2)
  The polarity of induced emf is given by
  A)
  Ampere's circuital law done clear
  B)
  Biot-Savart law done clear
  C)
  Lenz's law done clear
  D)
  Fleming's right and hand rule. done clear
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• question_answer3)
  Lenz's law is a consequence of the law of conservation of
  A)
  charge done clear
  B)
  mass done clear
  C)
  momentum done clear
  D)
  energy done clear
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• question_answer4)

  Near a circular loop of conducting wire as shown in the figure, an electron moves along a straight line.

  The direction of the induced current if any in the loop is

  A)
  variable done clear
  B)
  clockwise done clear
  C)
  anticlockwise done clear
  D)
  zero done clear
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• question_answer5)
  Two identical circular coils A and B are kept in a horizontal tube side by side without touching each other. If the current in the coil A increases with time, in response, the coil B
  A)
  is attracted by A done clear
  B)
  remains stationary done clear
  C)
  is repelled done clear
  D)
  rotates done clear
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• question_answer6)

  Directions : (6-10)

  Mutual inductance

  Mutual inductance is the phenomenon of inducing emf in a coil, due to a charge of current in the neighbouring coil. The amount of mutual inductance that links one coil to another depends very much on the relative positioning of the two coils, their geometry and relative separation between them. Mutual inductance between the two coils increases \[{{\mu }_{r}}\]times if the coils are wound over an iron core of relative permeability \[{{\mu }_{r}}\].

  A short solenoid of radius a, number of turns per unit length \[{{n}_{1}}\], and length L is kept coaxially inside a very long solenoid of radius b, number of turns per unit length \[{{n}_{2}}\]. What is the mutual inductance of the system ?
  A)
  \[{{\mu }_{0}}\pi {{b}^{2}}{{n}_{1}}{{n}_{2}}L\] done clear
  B)
  \[{{\mu }_{0}}\pi {{a}^{2}}{{n}_{1}}{{n}_{2}}{{L}^{2}}\] done clear
  C)
  \[{{\mu }_{0}}\pi {{a}^{2}}{{n}_{1}}{{n}_{2}}L\] done clear
  D)
  \[{{\mu }_{0}}\pi {{b}^{2}}{{n}_{1}}{{n}_{2}}{{L}^{2}}\] done clear
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• question_answer7)
  If a change in current of \[0\centerdot 01A\] in one coil produces a change in magnetic flux of \[2\times {{10}^{-2}}\] weber in another coil, then the mutual inductance between coils is
  A)
  0 done clear
  B)
  \[0\centerdot 5\,H\] done clear
  C)
  2H done clear
  D)
  3H done clear
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• question_answer8)
  Mutual inductance of two coils can be increased by
  A)
  decreasing the number of turns in the coils done clear
  B)
  increasing the number of turns in the coils done clear
  C)
  winding the coils on wooden cores done clear
  D)
  none of these done clear
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• question_answer9)
  When a sheet of iron is placed in between the two co-axial coils, then the mutual inductance between the coils will
  A)
  increase done clear
  B)
  decrease done clear
  C)
  remains same done clear
  D)
  cannot be predicted done clear
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• question_answer10)
  The SI units of mutual inductance is
  A)
  ohm done clear
  B)
  mho done clear
  C)
  henry done clear
  D)
  none of these. done clear
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• question_answer11)

  Directions : (11-15)

  Eddy Currents and Their Effects

  Currents can be induced not only in conducting coils, but also in conducting sheets or blocks. Current is induced in solid metallic masses when the magnetic flux threading through them changes. Such currents flow in the form of irregularly shaped loops throughout the body of the metal.

  These currents look like eddies or whirlpools in water so they are known as eddy currents. Eddy currents have both undesirable effects and practically useful applications.

  For example it causes unnecessary heating and wastage of power in electric motors, dynamos and in the cores of transformers.

  The working of speedometers of trains is based on
  A)
  wattless currents done clear
  B)
  eddy currents done clear
  C)
  alternating currents done clear
  D)
  pulsating currents. done clear
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• question_answer12)
  Identify the wrong statement
  A)
  Eddy currents are produced in a steady magnetic field done clear
  B)
  Induction furnace used eddy currents to produce heat done clear
  C)
  Eddy currents can be used to produce braking force in moving trains done clear
  D)
  Power meters work on the principle of Eddy currents. done clear
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• question_answer13)
  Which of the following is the best method to reduce eddy currents?
  A)
  Laminating core done clear
  B)
  Using thick wires done clear
  C)
  By reducing hysteresis loss done clear
  D)
  None of these. done clear
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• question_answer14)
  The direction of eddy currents is given by
  A)
  Fleming's left hand rule done clear
  B)
  Biot-Savart law done clear
  C)
  Lenz's law done clear
  D)
  Ampere-circuital law. done clear
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• question_answer15)
  Eddy current can be used to heat localised tissues of the human body. This branch of medical therapy is called
  A)
  Hyperthemia done clear
  B)
  Diathermy done clear
  C)
  Inductothermy done clear
  D)
  none of these done clear
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• question_answer16)

  Directions : (16-20)

  Self-Induction

  When a current I flows through a coil, flux linked with it is \[\phi =LI\], where L is a constant known as self-inductance of a coil Amy change in current sets up an induced e.m.f. in the coil. Thus, self-inductance of a coil is the induced emf set up in it when the current passing through it changes at the unit rate. It is a measure of the opposition to the growth or the decay of current flowing through H the coil. Also, value of self-inductance depends on the number of turns in the solenoid, its area of cross-section and the relative permeability of its core material.

  The inductance in a coil plays the same role as
  A)
  inertia in mechanics done clear
  B)
  energy in mechanics done clear
  C)
  momentum in mechanics done clear
  D)
  force in mechanics. done clear
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• question_answer17)
  A current of \[2\centerdot 5\,A\] flows through a coil of inductance 5 H. The magnetic flux linked with the coil is
  A)
  \[0\centerdot 5\,Wb\] done clear
  B)
  \[12\centerdot 5\,Wb\] done clear
  C)
  zero done clear
  D)
  2 Wb done clear
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• question_answer18)
  The-inductance L of a solenoid depends upon its radius R as
  A)
  \[L\propto R\] done clear
  B)
  \[L\propto 1/R\] done clear
  C)
  \[L\propto {{R}^{2}}\] done clear
  D)
  \[L\propto {{R}^{3}}\] done clear
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• question_answer19)
  The unit of self-inductance is
  A)
  weber ampere done clear
  B)
  weber\[^{-1}\] ampere done clear
  C)
  ohm second done clear
  D)
  farad done clear
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• question_answer20)
  The induced e.m.f. in a coil of 10 henry inductance in which current varies from 9 A to 4 A in \[0\centerdot 2\] secondary is
  A)
  200V done clear
  B)
  250V done clear
  C)
  300V done clear
  D)
  350V done clear
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• question_answer21)

  Directions : (21-25)

  The Experiments of Faraday and Henry

  In year 1820 Oersted discovered the magnetic effect of current. Faraday gave the through that reverse of this phenomenon is also possible i.e., current can also be produced by magnetic field. Faraday showed that when we move a magnet towards the coil which is connected by a sensitive galvanometer. The galvanometer gives instantaneous deflection showing that there is an electric current in the loop.

  Whenever relative motion between coil and magnet takes place an e.m.f. induced in coil. If coil is in closed circuit then current is also induced in the circuit. This phenomenon is called electromagnetic induction.

  The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a galvanometer. The magnet was held stationary for a few seconds with the North Pole in the middle of the solenoid and then withdrawn rapidly. The maximum deflection of the galvanometer was observed when the magnet was
  A)
  moving towards the solenoid done clear
  B)
  moving into the solenoid done clear
  C)
  at rest inside the solenoid done clear
  D)
  moving out of the solenoid done clear
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• question_answer22)
  Two similar circular loops carry equal curents in the same direction. On moving the coils further apart, the electric current will
  A)
  remain unaltered done clear
  B)
  increases in one and decreases in the second done clear
  C)
  increase in both done clear
  D)
  decrease in both. done clear
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• question_answer23)
  A closed iron ring is held horizontally and a bar magnetic is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is
  A)
  equal to g done clear
  B)
  less than g done clear
  C)
  more than g done clear
  D)
  depends on the diameter of the ring and length of magnet. done clear
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• question_answer24)
  Whenever there is a relative motion between a coil and a magnet, the magnitude of induced e.m.f. set up in the coil does not depend upon the
  A)
  relative speed between the coil and magnet done clear
  B)
  magnetic moment of the coil done clear
  C)
  resistance of the coil done clear
  D)
  number of turn in the coil. done clear
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• question_answer25)
  A coil of metal wire is kept stationary in a non-uniform magnetic field
  A)
  an e.m.f. and current both are induced in the coil done clear
  B)
  a current but no e.m.f. is induced in the coil done clear
  C)
  an e.m.f. but no current is induced in the coil done clear
  D)
  neither e.m.f. nor current is induced in the coil. done clear
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• question_answer26)

  Directions : (26-30)

  Motional EMF From Lorentz Force

  The e.m.f, induced across the ends of a conductor due to its motion in a magnetic field is called motional e.m.f. It is produced due to the magnetic Lorentz force acting on the free electrons of the conductor. For a circuit shown in figure, if a conductor of length l moves with velocity v in a magnetic field B perpendicular to both its length and the direction of the magnetic field, then all the induced parametres are possible in the circuit.

  Direction of current induced in a wire moving in a magnetic field is found using
  A)
  Fleming's left hand rule done clear
  B)
  Fleming's right hand rule done clear
  C)
  Ampere's rule done clear
  D)
  Right hand clasp rule. done clear
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• question_answer27)
  A conducting rod of length l is moving in a transeverse magnetic field of strength B with velocity v. The resistance of the rod is R. The current in the rod is
  A)
  \[\frac{Blv}{R}\] done clear
  B)
  \[B/v\] done clear
  C)
  zero done clear
  D)
  \[\frac{{{B}^{2}}{{v}^{2}}{{l}^{2}}}{R}\] done clear
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• question_answer28)
  \[A\,0\centerdot 1m\] long conductor carrying a current of 50 A is held perpendicular to a magnetic field of \[1\centerdot 25\,mT\]. The mechanical power required to move the conductor with a speed of \[1\,m\,{{s}^{-1}}\]is
  A)
  \[62\centerdot 5\,mW\] done clear
  B)
  \[625\,mW\] done clear
  C)
  \[6\centerdot 25\,mW\] done clear
  D)
  \[12\centerdot 5\,mW\] done clear
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• question_answer29)
  A bicycyle generator creates \[1\centerdot 5\,V\] at \[15\,km/hr\]. The EMF gererated at \[10\,km/hr\] is 
  A)
  \[1\centerdot 5\,Volts\] done clear
  B)
  2 volts done clear
  C)
  \[0\centerdot 5\,Volts\] done clear
  D)
  1 volt done clear
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• question_answer30)
  The dimensional formula for e.m.f. e is MKS system will be 
  A)
  \[\left[ M{{L}^{2}}{{T}^{-3}}{{A}^{-1}} \right]\] done clear
  B)
  \[\left[ M{{L}^{2}}{{T}^{-1}}A \right]\] done clear
  C)
  \[\left[ M{{L}^{2}}A \right]\] done clear
  D)
  \[\left[ ML{{T}^{-2}}{{A}^{-2}} \right]\] done clear
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