1. PHYSICS – Simple phenomena of magnetism

2. LEARNING OBJECTIVES Core
•Describe the forces between magnets, and between magnets and magnetic materials
• Give an account of induced magnetism • Distinguish between magnetic and non-magnetic materials
• Describe methods of magnetisation, to include stroking with a magnet, use of d.c. in a coil and hammering in a magnetic field
• Draw the pattern of magnetic field lines around a bar magnet
• Describe an experiment to identify the pattern of magnetic field lines, including the direction
• Distinguish between the magnetic properties of soft iron and steel
• Distinguish between the design and use of permanent magnets and electromagnets
Supplement
Explain that magnetic forces are due to interactions between magnetic fields
• Describe methods of demagnetisation, to include hammering, heating and use of a.c. in a coil

3. Magnets N S Properties Have magnetic fields around them. Attracted?
.. or not?
Magnets
Properties
Have magnetic fields around them. N S

4. Magnets N S Properties Have magnetic fields around them. Attracted?
.. may be?
Magnets
Properties
Have two opposite poles (N & S) – like poles repel, unlike poles attract.
Have magnetic fields around them. N S

5. Magnets N S Properties Have magnetic fields around them.
Attracted?
.. possibly?
Magnets
Properties
Have two opposite poles (N & S) – like poles repel, unlike poles attract.
Have magnetic fields around them. N S
Exert little or no force on a non-magnetic material.

6. Magnets N N S Properties Have magnetic fields around them.
Attracted?
.. hopefully?
Magnets
Properties
Have two opposite poles (N & S) – like poles repel, unlike poles attract.
Have magnetic fields around them. N S
Exert little or no force on a non-magnetic material.
Attract magnetic materials by inducing magnetism in them. N
Iron
Steel

7. Poles induced in both iron and steel.
Attracted?
.. mmmm?
Magnets
Properties
Have two opposite poles (N & S) – like poles repel, unlike poles attract.
Have magnetic fields around them. N S
Exert little or no force on a non-magnetic material.
Attract magnetic materials by inducing magnetism in them. N S S N N
Poles induced in both iron and steel.

8. Magnets N N S Properties Have magnetic fields around them.
Attracted?
YES!!!
Magnets
Properties
Have two opposite poles (N & S) – like poles repel, unlike poles attract.
Have magnetic fields around them. N S
Exert little or no force on a non-magnetic material.
Attract magnetic materials by inducing magnetism in them. N S N
Iron loses magnetism – it was only a temporary magnet
Steel retains magnetism – it became a permanent magnet

9. Magnets – make your own! N S How strong is it? Not very.
Placing a piece of steel near a magnet makes it permanently magnetised, but its magnetism is usually weak.

10. Wide sweep away from the steel
Magnets – make your own! N S
How strong is it?
Wide sweep away from the steel
Getting stronger. N S
Induced poles
The magnet can be magnetized more strongly by stroking it with one end of a magnet

11. Magnets – make your own! How strong is it? Steel Strongest! Coil
The best way of magnetizing is to place the steel bar in a long coil of wire and pass a large, direct (one way) current through the coil. The coil has a magnetic effect which magnetizes the steel.

12. Magnets – how do they work?
Just what is happening inside the magnet to make it magnetic?

13. Magnets – how do they work?
We need to look closely at what is happening to the particles (electrons) inside the magnet. N S
Just what is happening inside the magnet to make it magnetic?

14. Magnets – how do they work?
We need to look closely at what is happening to the particles (electrons) inside the magnet. N S
Just what is happening inside the magnet to make it magnetic?
In an unmagnetized material, the tiny electrons, or atomic magnets point in random directions.

15. Magnets – how do they work?
We need to look closely at what is happening to the particles (electrons) inside the magnet. N S
Just what is happening inside the magnet to make it magnetic?
When the material becomes magnetized, more and more of the tiny atomic magnets line up with each other. They act as one BIG magnet.

16. Magnets – how do they work?
We need to look closely at what is happening to the particles (electrons) inside the magnet. N S
Just what is happening inside the magnet to make it magnetic?
If a magnet is hit with a hammer, the tiny atomic magnets get thrown out of line again, so the material becomes demagnetised.

17. Magnets – how do they work?
We need to look closely at what is happening to the particles (electrons) inside the magnet. N S
Just what is happening inside the magnet to make it magnetic?
If a magnet is hit with a hammer, the tiny atomic magnets get thrown out of line again, so the material becomes demagnetised.
A magnet will also become demagnetized if heated to high temperature.

18. Magnetic and non-magnetic

19. Magnetic and non-magnetic
Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron).

20. Magnetic and non-magnetic
Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron).
Ferromagnets
Hard magnetic materials, eg. Steel, alloys (Alcomax, Magnadur). Difficult to magnetise, but do not lose their magnetism. Used for permanent magnets.

21. Magnetic and non-magnetic
Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron).
Ferromagnets
Hard magnetic materials, eg. Steel, alloys (Alcomax, Magnadur). Difficult to magnetise, but do not lose their magnetism. Used for permanent magnets.
Soft magnetic materials, eg. Iron, Mumetal. Relatively easy to magnetise, but magnetism is temporary. Used in electromagnets and transformers.

22. Magnetic and non-magnetic
Magnetic material – can be magnetized, and is attracted to magnets. Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is mainly iron).
Non-magnetic materials. Metals (brass, copper, zinc, tin and aluminium); non-metals.
Ferromagnets
Hard magnetic materials, eg. Steel, alloys (Alcomax, Magnadur). Difficult to magnetise, but do not lose their magnetism. Used for permanent magnets.
Soft magnetic materials, eg. Iron, Mumetal. Relatively easy to magnetise, but magnetism is temporary. Used in electromagnets and transformers.

23. Magnetic fields

24. Magnetic field lines around the magnet
Magnetic fields
Iron filings sprinkled around a magnet
Magnetic field lines around the magnet

25. Magnetic field lines around the magnet
Magnetic fields
Iron filings sprinkled around a magnet
Field lines run from the north pole (N) to the south pole (S). The magnetic field is strongest where the field lines are closer together.
Magnetic field lines around the magnet

26. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines. N S

27. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines. N S

28. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines. N S

29. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines. N S

30. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines. N S

31. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines. N S

32. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines. . . . . N S

33. Using a plotting compass to find the field lines.
Magnetic fields
Using a plotting compass to find the field lines.

34. Interactions between magentic fields
Magnetic fields
Interactions between magentic fields
When unlike poles are placed near each other, their magnetic fields combine to produce a single field of almost uniform strength.

35. Interactions between magentic fields
Magnetic fields
Interactions between magentic fields
Neutral point
When unlike poles are placed near each other, their magnetic fields combine to produce a single field of almost uniform strength.
When like poles are placed near each other, their magnetic fields cancel each other, and there is a neutral point where the combined field strength is zero.

36. The Earth’s magnetic field
The Earth’s magnetic field is like that around a very large, but very weak, bar magnet.

37. The Earth’s magnetic field
The Earth’s magnetic field is like that around a very large, but very weak, bar magnet.
A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north.

38. The Earth’s magnetic field
The Earth’s magnetic field is like that around a very large, but very weak, bar magnet.
A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north.
The Earth’s magnetic north is actually over 1200km away from the true geographic north pole.

39. The Earth’s magnetic field
Over a period of time the Earth’s magnetic pole will ‘flip’.
The Earth’s magnetic field is like that around a very large, but very weak, bar magnet.
A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north.
The Earth’s magnetic north is actually over 1200km away from the true geographic north pole.

40. The Earth’s magnetic field
Over a period of time the Earth’s magnetic pole will ‘flip’.
The Earth’s magnetic field is like that around a very large, but very weak, bar magnet.
A compass ‘north’ end points north. But a north pole is always attracted to a south pole, so the Earth’s magnetic south pole must actually be in the north.
The Earth’s magnetic north is actually over 1200km away from the true geographic north pole.
In the last 10 million years, there have been, on average, 4 or 5 ‘flips’ per million years.

41. Electromagnets
Distinguish between the design and use of permanent magnets and electromagnets

42. Electromagnets
Distinguish between the design and use of permanent magnets and electromagnets
Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off.

43. Electromagnets
Distinguish between the design and use of permanent magnets and electromagnets
Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off.
Permanent magnet uses:
Needles of compasses.
Fridge door seals, holding the doors closed.
Loudspeakers and microphones.

44. Electromagnets switch battery coil Soft iron core
Distinguish between the design and use of permanent magnets and electromagnets
switch
battery
Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off.
coil
Soft iron core
Permanent magnet uses:
Needles of compasses.
Fridge door seals, holding the doors closed.
Loudspeakers and microphones.
When a current flows through the coil it produces a magnetic field. This field is temporary and is lost when the current is switched off.

45. Electromagnets switch battery coil Soft iron core
Distinguish between the design and use of permanent magnets and electromagnets
switch
battery
Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off.
coil
Soft iron core
Permanent magnet uses:
Needles of compasses.
Fridge door seals, holding the doors closed.
Loudspeakers and microphones.
When a current flows through the coil it produces a magnetic field. This field is temporary and is lost when the current is switched off.
Strength increased by:
Increasing the current
Increasing number of turns

46. Electromagnets switch battery coil Soft iron core
Distinguish between the design and use of permanent magnets and electromagnets
switch
battery
Unlike bar magnets, which are permanent magnets, the magnetism of electromagnets can be turned on and off.
coil
Soft iron core
Permanent magnet uses:
Needles of compasses.
Fridge door seals, holding the doors closed.
Loudspeakers and microphones.
When a current flows through the coil it produces a magnetic field. This field is temporary and is lost when the current is switched off.
Strength increased by:
Increasing the current
Increasing number of turns
Uses: scrapyard electromagnets, circuit breakers, relays, electric bells.

47. LEARNING OBJECTIVES Core
•Describe the forces between magnets, and between magnets and magnetic materials
• Give an account of induced magnetism • Distinguish between magnetic and non-magnetic materials
• Describe methods of magnetisation, to include stroking with a magnet, use of d.c. in a coil and hammering in a magnetic field
• Draw the pattern of magnetic field lines around a bar magnet
• Describe an experiment to identify the pattern of magnetic field lines, including the direction
• Distinguish between the magnetic properties of soft iron and steel
• Distinguish between the design and use of permanent magnets and electromagnets
Supplement
Explain that magnetic forces are due to interactions between magnetic fields
• Describe methods of demagnetisation, to include hammering, heating and use of a.c. in a coil

48. PHYSICS – Simple phenomena of magnetism