Magnetism

1. Magnetism

2. Magnetism Introduction • Magnet is a object which shows the property of attracting magnetite materials towards itself and resting in N-S direction when suspended freely. • This property of magnet is called Magnetism.

3. Magnetic materials gold (Au) cobalt (Co) iron (Fe) nickel (Ni) copper (Cu) zinc (Zn) aluminium (Al) magnesium (Mg) silver (Ag)

4. Magnetic materials N S Ni Co Au Fe Cu Mg Zn Al Ag

5. P 11.1 (Properties of Magnets) • It attracts only ferro magnetic materials. • It has two opposite poles which are near the ends of a bar magnet and always occurs in pair. • Like pole repel & unlike pole attract.

6. Activity- Properties of poles

7. Magnetism can be induced in a magnetic material if it is placed within a magnetic field. If the material is magnetically hard it will retain its magnetism once removed from the field. Certain rocks in the Earth’s crust such as lodestone have been magnetised in this way by the Earth’s magnetic field. 11.2 (Induced magnetism) NS iron bar

8. When an unmagnetized substance is placed in a magnetic field, the substance can become magnetized. This happens when the spinning electrons line up in the same direction.

9. 11.3 (Magnetic field lines) • Space around a magnet, where a magnetic force is experienced. • Direction of field at a point can be found by a compass. • The shape of a magnetic field can be shown by iron filings or plotting compasses

10. PROPERTIES OF MFL • MFL travels from N to S outside the magnet and S to N inside the magnet. • They are close and continuous curve. • Magnetic field is strong where field lines are close together and weak where lines are apart. • Two magnetic field lines never intersect each other. • Direction of magnetic field is indicated by the arrow in the line at any point.

11. What is a magnetic field? N S The region around a magnet where it has a magnetic effect is called itsmagnetic field. When a magnetic material is placed in a magnetic field it will experience a force.

12. Shape of a magnetic field What is the shape and direction of the lines of force in the magnetic field around a bar magnet? strongest field at poles strongest field at poles S N weakest field further away from poles Where is the magnetic field strongest?

13. Magnetic fields: N pole together N S S N Draw the pattern created by the iron filings.

14. Magnetic field pattern: N poles together N S N S

15. Magnetic fields: N and S poles together N N S S Draw the pattern created by the iron filings.

16. Magnetic field pattern: N and S poles together N N S S

17. Magnetic fields between two bar magnets

18. P 11.4 (Magnetic property of Iron & steel ) • Magnetically hard- : Steel (alloy of Fe, Co & W) stay magnetic if once magnetised. Used in making permanent magnets. • Magnetically soft-: Pure iron, which do not stay magnetic.

19. Electromagnet *strong, temporary magnet formed when current is passed through a coil of wire surrounding an iron core. *acts like a bar magnet when current is on

20. P 11.5 (Uses of magnets ) When electricity is passed through a coil of wire, the coil has a magnetic field around it. This is called an electromagnet. If the coil of wire is wrapped around a piece of iron, such as an iron nail, the magnetic field gets stronger.

21. Investigating an electromagnet 1.Number of turnsaffects the number of paper clips attracted to an electromagnet – keep the current the same . 2.Amount of the current affects the number of paper clips attracted to an electromagnet –keep the number of turns the same.

22. Case-1

23. Case-2 0 12 23 38 49 60

26. Using electromagnets – scrap yards A large electromagnet is used in a scrap yard to pick up and move heavy pieces of scrap metal. What metals would the electromagnet attract? What advantages does an electromagnet have over a permanent magnet?

27. What is an electromagnet ? Why is soft iron generally used as core of the electromagnet? State two advantages of an electromagnet over a permanent magnet.

28. State three difference between a permanent magnet and an electromagnet. Give some uses of electromagnet.

29. Loudspeakers

30. Using electromagnets – door bells

31. Using electromagnets – relay Lifts, cars and other large electrical machines use high currents. A relay, which includes an electromagnet, is used to allow a small current in one circuit to control a large current in another circuit.

32. Magnets around the House: Headphones Refrigerator magnets Computer speakers Telephone receiversPhone ringers Microwave tubesSeal around refrigerator door Plug-in battery eliminatorsFloppy disk recording and reading headAudio tape recording and playback headVideo tape recording and playback headCredit card magnetic strip TV deflection coilComputer monitor Computer hard drive Shower curtain weights / attach to tubPower supply transformers

33. Using electromagnets Convert electrical energy into sound energy Using one circuit to turn another circuit off and on Used to break a circuit if the electrical current is too high Circuit breakers Relays Loudspeakers

34. The following links can help you learn more about magnets: • http://www.bbc.co.uk/schools/revisewise/science/physical/12_fact.shtml click next after reading the facts to take a quiz! • Complete this activity to explore magnetic fields http://www.galaxy.net/~k12/electric/fields.shtml • Ten facts about magnets: http://tm.wc.ask.com/r?t=c&s=a&id=30780&sv=za5cb0dc7&uid=2d0b7690bd0b7690b&sid=3d0b7690bd0b7690b&p=%2flinks&o=0&u=http://www.execpc.com/~rhoadley/magbasic.htm