JAMB Physics questions: Electromagnetic induction

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

1. Question 1· 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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2. Question 2· 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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3. Question 3· 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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4. Question 4· 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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5. Question 5· 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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6. Question 6· 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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7. Question 7· 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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8. Question 8· 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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9. Question 9· 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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10. Question 10· 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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11. Question 11· 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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12. Question 12· Electromagnetic induction· JAMB

    A transformer works on the principle of

    • Amutual induction
    • Bself-induction only
    • Cthe heating effect of current
    • Delectrolysis

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13. Question 13· Electromagnetic induction· JAMB

    Electric power is transmitted over long distances at very high voltage mainly to

    • Amake the cables lighter
    • Bincrease the current
    • Creduce energy lost as heat in the cables
    • Dincrease the frequency

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14. Question 14· Electromagnetic induction· JAMB

    A transformer steps 240 V down to 12 V. If the secondary coil has 50 turns, the primary has

    • A2.5 turns
    • B1,000 turns
    • C20 turns
    • D50 turns

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    Explanation and discussion