12th Class Physics Electro Magnetic Induction Question Bank

done Case Based (MCQs) - Electromagnetic Induction Total Questions - 40

• question_answer1)

  Direction: Q.1 to Q.5

  The induced electromotive force with different polarities induces a current whose magnetic field opposes the change in magnetic flux through the loop in order to ensure that original flux is maintained through the loop when current flows in it.

  To batter understand Lenz's law, let us consider two cases:

  Case 1: When a magnet is moving towards the coil.

  When the north pole of the magnet is approaching towards the coil, the magnetic flux linking to the coil increases. According to Faraday's law of electromagnetic induction, when there is a change in flux, an emf, and hence current is induced in the coil and this current will create its own magnetic field.

  Now according to Lenz's law, this magnetic field created will oppose its own or we can say opposes the increase in flux through the coil and this is possible only if approaching coil side attains north polarity, as we know similar poles repel each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in the anticlockwise direction.

  Case 2: When a magnet is moving away from the coil

  When the north pole of the magnet is moving away from the coil, the magnetic flux linking to the coil decreases. According to Faraday's law of electromagnetic induction, an emf and hence current is induced in the coil and this current will create its own magnetic field.

  Now according to Lenz's law, this magnetic field created will oppose its own or we can say opposes the decrease in flux through the coil and this is possible only if approaching coil side attains south polarity, as we know dissimilar poles attract each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in a clockwise direction.

  Read the above passage carefully and give the answer of the following questions:

  What is the direction of the induced magnetic field?
  A)
      left        done clear
  B)
  right done clear
  C)
  up                     done clear
  D)
              down done clear
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• question_answer2)
  What is the direction of the induced magnetic field? Magnet moving up
  A)
  left       done clear
  B)
              right     done clear
  C)
  up                                 done clear
  D)
  down done clear
  View Solution play_arrow

• question_answer3)
  In what direction is the magnet moving?
  A)
  left    done clear
  B)
  right     done clear
  C)
  cup                               done clear
  D)
  down done clear
  View Solution play_arrow

• question_answer4)
                 In what direction is the magnet moving?              
  A)
  left    done clear
  B)
  right     done clear
  C)
  cup                               done clear
  D)
  down done clear
  View Solution play_arrow

• question_answer5)
  Which of the following is NOT an application of Lenz's Law
  A)
  Transformer done clear
  B)
  AC Generator done clear
  C)
  DC Motor done clear
  D)
  A coil transversed by AC current done clear
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• question_answer6)

  Direction: Q.6 to Q.10

  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 flows in such a direction so as to create a magnetic flux in the direction of the original flux.

  Read the above passage carefully and give the answer of the following questions:

  Which of the following statement is correct?
  A)
  The 'induced emf is not in the direction opposing the change in magnetic flux so as to oppose the cause which produces 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_answer7)
  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 hand rule done clear
  View Solution play_arrow

• question_answer8)
  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_answer9)
  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_answer10)
  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_answer11)

  Direction: Q.11 to Q.15

  The emf induced across the ends of a conductor

  due to its motion in a magnetic field is called motional emf. 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 parameters are possible in the circuit.

  Read the above passage carefully and give the answer of the following questions:

  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_answer12)
  A conducting rod of length l is moving in a transverse 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)
  \[Blv\] done clear
  C)
  zero                   done clear
  D)
              \[\frac{{{B}^{2}}{{v}^{2}}{{l}^{2}}}{R}\] done clear
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• question_answer13)
  A 0.1 m long conductor carrying a current of 50A is held perpendicular to a magnetic field of 1.25 mT. The mechanical power required to move the conductor with a speed of \[1\text{ }m{{s}^{-1}}\] is:
  A)
  62.5 mW done clear
  B)
  625 mW done clear
  C)
  6.25 mW                       done clear
  D)
  12.5 mW done clear
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• question_answer14)
  A bicycle generator creates 1.5 V at 15 km/hr. The EMF generated at 10 km/hr is:
  A)
  1.5 volts                        done clear
  B)
  2 volts   done clear
  C)
  0.5 volts                        done clear
  D)
  1 volt done clear
  View Solution play_arrow

• question_answer15)
  The dimensional formula for emf \[\varepsilon \] in MKS system will be:
  A)
              \[[M{{L}^{2}}{{T}^{-3}}{{A}^{-1}}]\]                  done clear
  B)
  \[[M{{L}^{2}}{{T}^{-1}}A]\] done clear
  C)
              \[[M{{L}^{2}}A]\]        done clear
  D)
              \[[ML{{T}^{-2}}{{A}^{-2}}]\] done clear
  View Solution play_arrow

• question_answer16)

  Direction: Q.16 to Q.20

  Current 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.

  Read the given passage carefully and give the answer of the following questions:

  The working of speedometers of trains is based on:
  A)
  wattles currents               done clear
  B)
  eddy currents done clear
  C)
  alternating currents   done clear
  D)
  pulsating currents done clear
  View Solution play_arrow

• question_answer17)
  Identify the wrong statement:
  A)
  Eddy currents are produced in a steady magnetic field. done clear
  B)
  Induction furnace use eddy currents to produce heat. done clear
  C)
  Eddy currents can be used to produce breaking force in moving trains.                                         done clear
  D)
  Power meters work on the principle of eddy currents. done clear
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• question_answer18)
  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_answer19)
                               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
  View Solution play_arrow

• question_answer20)
  Eddy currents can be used to heat localised tissues of the human body. This branch of medical therapy is called:
  A)
  Hyperthermia                 done clear
  B)
  Diathermy done clear
  C)
  Inductothermy                done clear
  D)
  none of these done clear
  View Solution play_arrow

• question_answer21)

  Direction: Q.21 to Q.25

  An eddy current is a current set up in a conductor in response to a changing magnetic field. They flow in closed loops in plane perpendicular to the magnetic field. By Lenz's law, the current swirls in such a way as to create a magnetic field opposing the change; for this to occur in a conductor, electrons swirl in a plane perpendicular to the magnetic field.

  Because of the tendency of eddy currents to oppose, eddy currents cause a loss of energy. Eddy currents transform more useful forms of energy. Eddy currents can also be removed by cracks or slits in the conductor, which break the circuit and prevent the current loops from circulating. This means that eddy currents can be used to detect defects in materials. This is called non destructive testing and is often used in airplanes. The magnetic field produced by the eddy currents is measured, where a change in the field reveals the presence of an irregularity a defect will reduce the size of the eddy current, which in turn reduces the magnetic field strength.

  Another application of eddy currents is magnetic levitation. Conductors are exposed to varying magnetic fields which induce eddy currents within the conductor and produce a repulsive magnetic field, pushing the magnet and conductor apart. This alternating magnetic field can be caused by relative motion between the magnet and conductor (generally the magnet is stationary and the conductor moves) or with an electromagnet applied with a varying current to very the magnetic field strength.

  Read the above passage carefully and give the answer of the following questions:

  What is the heat generated in eddy current operations?
  A)
  \[Vl\]                             done clear
  B)
  \[VlR\] done clear
  C)
  \[{{l}^{2}}RT\]            done clear
  D)
              \[{{l}^{2}}R\] done clear
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• question_answer22)
  With an increase in the density of the material, the power loss in eddy current:
  A)
  increases       done clear
  B)
  decreases done clear
  C)
  does not change              done clear
  D)
  not related done clear
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• question_answer23)
  Generation of eddy currents depends on the principle of:
  A)
  wave guide theory done clear
  B)
  electromagnetic induction             done clear
  C)
  magneto-restrictive force done clear
  D)
  All of the above done clear
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• question_answer24)
  Eddy currents generated in a test object flow:
  A)
  in the same plane as magnetic flux done clear
  B)
  in the same plane as the coil is wound done clear
  C)
  \[90{}^\circ \] to the coil winding plane done clear
  D)
  Eddy currents have no predictable direction done clear
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• question_answer25)
  The discovery of electromagnetic induction is credited to:
  A)
  Arago                            done clear
  B)
  Oersted done clear
  C)
  Maxwell                         done clear
  D)
  Faraday done clear
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• question_answer26)

  Direction: Q.26 to Q.30

  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\[{{\mu }_{r}}\].

  Read the above passage carefully and give the answer of the following questions:

  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
  View Solution play_arrow

• question_answer27)
  If a change in current of 0.01 A 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)
  0.5 H done clear
  C)
  2 H                               done clear
  D)
  3 H done clear
  View Solution play_arrow

• question_answer28)
  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 the above done clear
  View Solution play_arrow

• question_answer29)
  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_answer30)
  The SI unit of mutual inductance is:
  A)
  ohm                  done clear
  B)
  mho    done clear
  C)
  henry                            done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer31)

  Direction: Q.31 to Q.35

  Mutual inductance between the two coils is defined as the property of the coil due to which it opposes the change of current in the other coil, or you can say in the neighbouring coil. When the current in the neighbouring coil changes, the flux sets up in the coil and because of this, changing flux emf is induced in the coil called mutually induced emf and the phenomenon is known as mutual inductance.

  The value of mutual inductance (M) depends upon the following factors:

  1. Number of turns in the secondary or neighbouring coil,

  2. Cross-sectional area,

  3. Closeness of the two coils.

  When on a magnetic core, two or more than two coils are wound, the coils are said to be mutually coupled. The current, when passed in any of the coils wound around the magnetic core, produces flux which links all the coils together and also the one in which current is passed. Hence, there will be both self-induced emf and mutual induced emf in each of the coils. The best example of the mutual inductance is the transformer, which works in the principle of Faraday's Law of Electromagnetic induction.

  Faraday's law of electromagnetic induction states that, "the magnitude of voltage is directly proportional to the rate of change of flux."

  Read the above passage carefully and give the answer of the following questions:

  The phenomenon due to which there is an induced current in one coil due to current in a neighbouring coil is?
  A)
  Electromagnetism            done clear
  B)
  Susceptance done clear
  C)
  Mutual inductance          done clear
  D)
  Steady current done clear
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• question_answer32)
  Mutual inductance between two magnetically coupled coils depends on:
  A)
  permeability of the core material done clear
  B)
  number of the turns of the coils done clear
  C)
  cross sectional area of their common core done clear
  D)
  All of the above done clear
  View Solution play_arrow

• question_answer33)
  Which of the following is unit of inductance?
  A)
  Ohm       done clear
  B)
  Henry done clear
  C)
  Ampere            done clear
  D)
  Webers/meter done clear
  View Solution play_arrow

• question_answer34)
  Which of the following circuit elements will oppose the change in circuit current?
  A)
  Capacitance                   done clear
  B)
  Inductance done clear
  C)
  Resistance                      done clear
  D)
  All of these done clear
  View Solution play_arrow

• question_answer35)
  If in an iron cored coil the iron core is removed so as to make the air cored coil, the inductance of the coil will be
  A)
  more                done clear
  B)
  less done clear
  C)
  the same           done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer36)

  Direction: Q.36 to Q.40

  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 the coil. Any change in current sets up an induced emf in the coil. Thus, self inductance of a coil is the induced emf set up in the coil 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 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.

  Read the above passage carefully and give the answer of the following questions:

  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_answer37)
  A current of 2.5 A flows through a coil of inductance 5H. The magnetic flux linked with the coil is:
  A)
  0.5 Wb  done clear
  B)
  12.5 Wb done clear
  C)
  zero                   done clear
  D)
  2 Wb done clear
  View Solution play_arrow

• question_answer38)
  The inductance L of a solenoid depends upon its radius R as:
  A)
  \[L\propto R\]                 done clear
  B)
  \[L\propto l/R\] done clear
  C)
  \[L\propto {{R}^{2}}\]              done clear
  D)
  \[L\propto {{R}^{3}}\] done clear
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• question_answer39)
  The unit of self-inductance is:
  A)
  weber ampere       done clear
  B)
  \[\text{webe}{{\text{r}}^{\text{-1}}}\text{ampere}\] done clear
  C)
  ohm second         done clear
  D)
  farad done clear
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• question_answer40)
   The induced e.m.f. in a coil of 10 henry inductance in which current varies from 9 A to 4 A in 0.2 second is:
  A)
  200 V                done clear
  B)
  250 V done clear
  C)
  300 V                done clear
  D)
  350 V    done clear
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