JAMB and WAEC Physics questions: Electromagnetic induction

25 questions with answers and explanations. Tap an option to check yourself.

1. Question 1· Electromagnetic induction· WAEC

   The iron core of a transformer is laminated in order to reduce

   • Aeddy current losses
   • Bthe resistance of the coils
   • Cthe flux linkage
   • Dthe output voltage

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   Explanation and discussion

2. Question 2· Electromagnetic induction· JAMB

   Faraday's law states that the induced e.m.f. is proportional to the

   • Arate of change of magnetic flux linkage
   • Bresistance of the coil
   • Ccurrent in the coil
   • Darea of the coil only

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3. Question 3· Electromagnetic induction· WAEC

   When a magnet's north pole is pushed into a coil, the induced current makes the near end of the coil a north pole. This illustrates

   • ALenz's law
   • BCoulomb's law
   • COhm's law
   • DNewton's first law

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4. Question 4· Electromagnetic induction· JAMB

   In a step-up transformer, the secondary coil has

   • Amore turns than the primary coil
   • Bfewer turns than the primary coil
   • Cthe same number of turns
   • Dno turns

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5. Question 5· Electromagnetic induction· WAEC

   Transformers do not work with direct current because

   • Ad.c. does not produce a changing magnetic field
   • Bd.c. is too strong
   • Cd.c. has no voltage
   • Dthe core melts

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6. Question 6· Electromagnetic induction· WAEC

   A transformer has 100 turns in the primary and 500 in the secondary. With 240 V input, the output is

   • A48 V
   • B1,200 V
   • C240 V
   • D600 V

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7. Question 7· Electromagnetic induction· JAMB

   A transformer has 200 turns in the primary and 1000 turns in the secondary. If the primary voltage is 40 V, the secondary voltage is:

   • A8 V
   • B400 V
   • C200 V
   • D5 V

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8. Question 8· Electromagnetic induction· WAEC

   The device that changes mechanical energy into electrical energy is the

   • Aelectric motor
   • Btransformer
   • Cgenerator
   • Dbattery

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9. Question 9· Electromagnetic induction· WAEC

   A step-up transformer has 50 turns on its primary and 1,000 turns on its secondary. Find the output for a 12 V input.

   • A240 V
   • B0.6 V
   • C600 V
   • D12 V

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10. Question 10· Electromagnetic induction· JAMB

    A step-down transformer changes 240 V to 12 V. If the primary coil has 2000 turns, how many turns has the secondary?

    • A200
    • B40 000
    • C100
    • D20

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11. Question 11· Electromagnetic induction· WAEC

    A transformer has 100 turns on the primary coil and 500 turns on the secondary. If the primary voltage is 20 V, the secondary voltage is

    • A4 V
    • B100 V
    • C2,500 V
    • D400 V

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12. Question 12· Electromagnetic induction· JAMB

    An a.c. generator differs from a d.c. generator mainly in having

    • Ano coil
    • Bslip rings instead of a split-ring commutator
    • Cno magnet
    • Diron brushes

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13. Question 13· Electromagnetic induction· JAMB

    An a.c. generator converts

    • Achemical energy into electrical energy
    • Belectrical energy into mechanical energy
    • Cheat into light
    • Dmechanical energy into electrical energy

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14. Question 14· Electromagnetic induction· WAEC

    Lenz's law is a consequence of the conservation of

    • Amomentum
    • Bmass
    • Ccharge
    • Denergy

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15. Question 15· Electromagnetic induction· JAMB

    A transformer that is 90% efficient delivers 180 W. Find its input power.

    • A162 W
    • B200 W
    • C180 W
    • D270 W

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16. Question 16· Electromagnetic induction· JAMB

    The direction of an induced current is given by:

    • ALenz's law
    • BFleming's left-hand rule
    • COhm's law
    • DCoulomb's law

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17. Question 17· Electromagnetic induction· WAEC

    A dynamo converts

    • Amechanical energy into electrical energy
    • Belectrical energy into mechanical energy
    • Cheat into light
    • Dchemical energy into electrical energy

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18. Question 18· Electromagnetic induction· JAMB

    Energy losses due to eddy currents in a transformer core are reduced by

    • Ausing thicker wire
    • Blaminating the core
    • Cusing a solid iron core
    • Dincreasing the voltage

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19. Question 19· Electromagnetic induction· JAMB

    Faraday's law states that the induced e.m.f. in a circuit is proportional to the

    • Anumber of cells
    • Bstrength of the magnet only
    • Cresistance of the circuit
    • Drate of change of magnetic flux linkage

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20. Question 20· Electromagnetic induction· JAMB

    A transformer does not work with a steady direct current because

    • Ad.c. overheats the core
    • Bd.c. is too weak
    • Ca steady current produces no changing magnetic flux
    • Dthe coils would melt

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    Explanation and discussion