Magnets, Electromagnetism and Induction

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.Like magnetic poles:

   • A.attract each other
   • B.have no effect
   • C.repel each other✓ Correct Answer
   • D.cancel each other

   Explanation: North repels north and south repels south.

2. Q2.The SI unit of magnetic field (magnetic flux density) is:

   • A.weber
   • B.tesla✓ Correct Answer
   • C.henry
   • D.gauss only

   Explanation: One tesla is one weber per square metre.

3. Q3.A freely suspended bar magnet comes to rest along the:

   • A.east-west direction
   • B.vertical direction only
   • C.north-south direction✓ Correct Answer
   • D.any direction

   Explanation: It aligns with the Earth's magnetic field.

4. Q4.Oersted discovered that:

   • A.an electric current produces a magnetic field✓ Correct Answer
   • B.a magnet produces gravity
   • C.light is a wave
   • D.charge is quantised

   Explanation: A compass needle deflected near a current-carrying wire.

5. Q5.Which of the following is attracted by a magnet?

   • A.wood
   • B.plastic
   • C.iron✓ Correct Answer
   • D.glass

   Explanation: Iron is ferromagnetic.

6. Q6.Magnetic field lines outside a bar magnet go from:

   • A.south pole to north pole
   • B.north pole to south pole✓ Correct Answer
   • C.east to west
   • D.centre to the ends only

   Explanation: Inside the magnet they run from south to north, forming closed loops.

7. Q7.Fleming's left-hand rule gives the direction of:

   • A.induced current
   • B.electric field
   • C.magnetic flux
   • D.force on a current-carrying conductor in a magnetic field✓ Correct Answer

   Explanation: It is the principle of the electric motor.

8. Q8.Fleming's right-hand rule gives the direction of:

   • A.induced current✓ Correct Answer
   • B.force on a charge
   • C.magnetic field of a magnet
   • D.current in a cell

   Explanation: It is used for generators.

9. Q9.Electromagnetic induction was discovered by:

   • A.Hans Oersted
   • B.Michael Faraday✓ Correct Answer
   • C.James Maxwell
   • D.Alessandro Volta

   Explanation: Faraday showed that a changing flux induces an emf in 1831.

10. Q10.A transformer works on the principle of:

    • A.self induction only
    • B.Ohm's law
    • C.photoelectric effect
    • D.mutual induction (with alternating current)✓ Correct Answer

    Explanation: It does not work with steady direct current.

11. Q11.An electric motor converts:

    • A.electrical energy into mechanical energy✓ Correct Answer
    • B.mechanical energy into electrical energy
    • C.light into heat
    • D.sound into light

    Explanation: A generator does the opposite.

12. Q12.Which of the following is a ferromagnetic material?

    • A.copper
    • B.gold
    • C.zinc
    • D.cobalt✓ Correct Answer

    Explanation: Iron, cobalt and nickel are the common ferromagnetic metals.

13. Q13.The weber is the unit of:

    • A.magnetic flux✓ Correct Answer
    • B.magnetic field
    • C.inductance
    • D.charge

    Explanation: Flux is field times area.

14. Q14.Above the Curie temperature a ferromagnetic material becomes:

    • A.diamagnetic
    • B.paramagnetic✓ Correct Answer
    • C.a superconductor
    • D.a stronger magnet

    Explanation: Heat destroys the alignment of magnetic domains.

15. Q15.The right-hand thumb rule gives the direction of:

    • A.the force on a charge
    • B.the induced emf
    • C.the magnetic field around a current-carrying wire✓ Correct Answer
    • D.the electric field

    Explanation: Thumb along the current, fingers curl along the field.

16. Q16.A step-up transformer has:

    • A.fewer turns in the secondary
    • B.equal turns in both
    • C.more turns in the secondary than in the primary✓ Correct Answer
    • D.no secondary coil

    Explanation: The output voltage is higher than the input.

17. Q17.Lenz's law states that the induced current:

    • A.aids the change in flux
    • B.is always zero
    • C.is independent of the flux
    • D.opposes the change in flux that produces it✓ Correct Answer

    Explanation: It reflects conservation of energy.

18. Q18.The core of an electromagnet is made of:

    • A.steel
    • B.copper
    • C.aluminium
    • D.soft iron✓ Correct Answer

    Explanation: Soft iron magnetises and demagnetises easily.

19. Q19.Permanent magnets are usually made of:

    • A.soft iron
    • B.steel and certain alloys✓ Correct Answer
    • C.copper
    • D.rubber

    Explanation: They retain magnetism for a long time.

20. Q20.The magnetic field inside a long current-carrying solenoid is:

    • A.nearly uniform✓ Correct Answer
    • B.zero
    • C.strongest at the ends only
    • D.random

    Explanation: Field lines inside are parallel to the axis.