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8 j magnets & electromagnets (boardworks)

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8 j magnets & electromagnets (boardworks)

  1. 1. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20051 of 29 KS3 Physics 8J Magnets and Electromagnets
  2. 2. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20052 of 29 8J Magnets and Electromagnets Contents Magnetic materials Magnetic fields Electromagnets Summary activities
  3. 3. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20053 of 29 Which of the metals below are magnetic metals? aluminium (Al) silver (Ag) iron (Fe) gold (Au) nickel (Ni) cobalt (Co) copper (Cu) zinc (Zn) magnesium (Mg) Magnetic materials
  4. 4. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20054 of 29 N S Al ZnAg Cu Au Mg Fe Ni Co A magnetic material is attracted to a magnet. Magnetic materials Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic.
  5. 5. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20055 of 29 8J Magnets and Electromagnets Contents Magnetic materials Magnetic fields Electromagnets Summary activities
  6. 6. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20056 of 29 Forces between magnets – experiment
  7. 7. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20057 of 29 NS The iron filings feel the effect of the magnetic field and show the direction of the forces in this region. The region around a magnet where it has a magnetic effect is called its magnetic field. When a magnetic material is placed in a magnetic field it will experience a force. What is a magnetic field?
  8. 8. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20058 of 29 weakest field further away from poles What is the shape and direction of the lines of force in the magnetic field around a bar magnet? N S Shape of a magnetic field Where is the magnetic field strongest? strongest field at poles strongest field at poles
  9. 9. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20059 of 29 Bring the north poles of two bar magnets together. What happens to the magnets? Viewing magnetic fields: N poles together N SS N Next, bring the two north poles as close to each other as possible and place a piece of paper on top of the magnets. Carefully scatter iron filings onto the paper. Draw the pattern created by the iron filings.
  10. 10. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200510 of 29 NNS S Magnetic field pattern: N poles together What do you notice about the pattern of the lines of force in the region between the two north poles?
  11. 11. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200511 of 29 Bring the north and south poles of two bar magnets together. What happens to the magnets? Viewing magnetic fields: N and S poles together S N S N Next, put the north and south poles close to each other, without letting them touch, and place a piece of paper on top. Carefully scatter iron filings onto the paper. Draw the pattern created by the iron filings.
  12. 12. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200512 of 29 NN How does this pattern compare with the pattern between the two north poles? Magnetic field pattern: N and S poles together What do you notice about the pattern of the lines of force in the region between the north and south poles? S S
  13. 13. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200513 of 29 1. When two like poles (e.g. two north poles or two south poles) are put together, they repel each other. Magnetic fields – summary 2. When two unlike poles (e.g. a north and a south pole) are put together, they attract each other. 3. Scattering iron filings around a bar magnets makes it possible to see the lines of force of the magnetic field.
  14. 14. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200514 of 29 A magnet can be made by magnetizing a material which is attracted to a magnet, e.g. a paper clip. Stroke a magnet along the paperclip from one end to the other and then starting from the same place, repeat the movement. The more times this is done, the more magnetic the clip becomes. Hold a nail in a magnetic field and hit it with a hammer. Put a magnetic material in a strong magnetic field. Making a magnet There are three methods that can be used to make a magnet:
  15. 15. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200515 of 29 8J Magnets and Electromagnets Contents Magnetic materials Magnetic fields Electromagnets Summary activities
  16. 16. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200516 of 29 Making an electromagnet 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.
  17. 17. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200517 of 29 An iron core at the centre of a coil of wire, increases the strength of an electromagnet. Two experiments can be carried out to investigate the other factors that can affect the strength of an electromagnet: Investigating an electromagnet 1. Investigate how the number of coils affects the number of paper clips attracted to an electromagnet – keep the current the same in this experiment. 2. Investigate how the size of the current affects the number of paper clips attracted to an electromagnet – keep the number of coils the same in this experiment.
  18. 18. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200518 of 29 Number of coils Number of paper clips attracted 0 20 40 60 80 Remember – keep the current the same throughout this experiment! Investigating an electromagnet – results 1 0 8 18 31 46
  19. 19. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200519 of 29 Current (A) Number of paper clips attracted 0 1 2 3 4 5 Remember – keep the number of coils the same throughout this experiment! Investigating an electromagnet – results 2 0 12 23 38 49 60
  20. 20. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200520 of 29 Graph to show how the number of coils affects the strength of an electromagnet 0 10 20 30 40 50 0 20 40 60 80 100 number of coils numberofclipsattracted Investigating an electromagnet – graph 1
  21. 21. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200521 of 29 Graph to show how the current affects the strength of an electromagnet 0 10 20 30 40 50 60 70 0 1 2 3 4 5 current (A) numberofclipsattracted Investigating an electromagnet – graph 2
  22. 22. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200522 of 29 What advantages does an electromagnet have over a permanent magnet? What metals would the electromagnet attract? A large electromagnet is used in a scrap yard to pick up and move heavy pieces of scrap metal. Using electromagnets – scrap yards
  23. 23. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200523 of 29 The circuit for a door bells includes an electromagnet. Using electromagnets – door bells
  24. 24. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200524 of 29 Lifts, cars and other large electrical machines use high currents. Using electromagnets – relay A relay, which includes an electromagnet, is used to allow a small current in one circuit to control a large current in another circuit.
  25. 25. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200525 of 29 1. When electricity is passed through a coil of wire, the coil behaves like a magnet and has a magnetic field around it – this is an electromagnet. Electromagnets – summary  wrap the coil of wire around an iron core;  increase the number of coils;  increase the size of the current. 3. An electromagnet can be easily turned on and off. This is why electromagnets can be used in scrapyards and as switches in electrical devices. 2. There are three ways to make an electromagnet stronger:
  26. 26. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200526 of 29 8J Magnets and Electromagnets Contents Magnetic materials Magnetic fields Electromagnets Summary activities
  27. 27. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200527 of 29 Glossary attraction – The force that pulls things together, e.g. opposite poles of two magnets. electromagnet – A magnet made by passing electricity through a coil of wire, which often has a core inside. magnet – An object that has a magnetic field and can attract magnetic materials. magnetic field – The area around a magnet where its magnetic force can be felt. magnetic materials – Materials that are attracted to a magnet, e.g. iron, cobalt and nickel. magnetism – The non-contact force of a magnetic field. poles – The parts of a magnet where its magnetic field is strongest. repulsion – The force that pushes things away from each other, e.g. similar poles of two magnets.
  28. 28. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200528 of 29 Anagrams
  29. 29. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200529 of 29 Multiple-choice quiz

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