Unit 10: Magnetism

Unit 10: Magnetism

1. Explain why the two ends of a bar magnet are called the north-seeking pole and the south-seeking pole

   • It is due to the Earth's magnetic field - the north-seeking pole points to the North Pole (the Earth's magnetic south pole) and the south-seeking pole points to the South Pole (the Earth's magnetic north pole).

2. Recall that like poles repel and unlike poles attract

   • like poles repel (N v N, S v S) and unlike poles attract (N + S, S + N)

3. Describe what is meant by magnetic induction

   • magnetism induced in an unmagnetised ferrous (a material that contains iron) bar by holding a permanent magnet near it

4. Recall the pattern of magnetic field lines round a bar magnet

   • the magnetic field lines of a bar magnet curve from the north pole of the bar magnet round to the south pole

5. Describe an experiment to plot the field lines of a magnetic field

6. Describe how to magnetise and demagnetise a magnetic material

   • an iron or steel bar can be magnetised by:
     • repeatedly moving the N-pole of a bar magnet along the bar in the same direction or withdrawing the bar from a long coil carrying a direct current
   • an iron or steel bar can be demagnetised by:
     • repeatedly moving the S-pole of a bar magnet along the bar in the same direction or withdrawing the bar from a long coil carrying an alternating current

7. Explain the meaning of 'hard' and 'soft' magnetic materials

   • A 'hard' magnetic material is harder to magnetise and demagnetise than a 'soft' magnetic material

8. Distinguish between iron and steel in terms of their magnetic properties

   • Iron is soft, steel is hard

9. Explain why iron is used in an electromagnet and steel is used to make a permanent magnet

   • Iron rather than steel is used in an electromagnet because iron can be magnetised and demagnetised more easily than steel. That is why steel and not iron is used to make a permanent magnet, because much more energy is needed to make the atoms in steel move out of their overall alignment.

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