Magnetism

1. Magnetism

2. Magnets • magnetism – force of attraction or repulsion • not all objects are affected by the force of magnetism • ex. wood, glass, paper, plastic • common metals affected by magnetism are iron, nickel, and cobalt

3. Magnets • Atoms themselves have magnetic properties due to the spin of the atom’s electrons. • Groups of atoms join so that their magnetic fields are all going in the same direction • These areas of atoms are called “domains”

4. Magnets 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.

5. Magnets • poles – two ends of a magnet • every magnet has two poles • north (N) pole • south (S) pole • even if you break a magnet in half, each half will have a north pole and a south pole

6. Properties of Magnets • like magnetic poles repel each other • unlike magnetic poles attract each other

7. Magnetic Fields • magnetic field – area around a magnet where magnetic forces can act • a magnetic field is made up of magnetic lines of force

8. Magnetic Fields • magnetic lines of force – lines that show the shape of a magnetic field • the magnetic lines of force are closest together at the poles of the magnet • this is where the magnet is strongest

9. Field Lines Around a Bar Magnet

10. Field Lines of Repelling Bars

11. Field Lines of Attracting Bars

12. If you cut a magnet in half, S N S N S N you get 2 magnets!

13. The Earth as a Magnet • the Earth has a North Magnetic Pole and a South Magnetic Pole • the North Magnetic Pole is located near the geographic North Pole • the South Magnetic Pole is located near the geographic South Pole

14. The Earth as a Magnet • the North Magnetic Pole is like the south pole of a bar magnet • the South Magnetic Pole is like the north pole of a bar magnet

15. The Earth as a Magnet • the Earth is surrounded by a magnetic field which extends far into space • magnetosphere – region of the Earth’s magnetic field

16. The Earth as a Magnet • the magnetosphere traps charged particles from the sun • when these particles enter the atmosphere, an aurora is formed • auroras are also called the northern and southern lights

17. Electricity and Magnetism • an electric current passing through a wire causes a magnetic field

18. Electricity and Magnetism • electromagnetism – relationship between electricity and magnetism

19. Electricity and Magnetism • electromagnetic induction – process by which an electric current is produced by moving a wire in a magnetic field

20. Electricity and Magnetism • a wire carrying an electric current always has a magnetic field around it • the magnetic field in a straight wire is not very strong • if the wire is wound into a coil, the magnetic field becomes much stronger as the individual magnetic fields overlap • the greater the number of coils, the stronger the magnetic field

21. Electromagnets • electromagnet – temporary magnet made by wrapping a current-carrying wire around an iron core • the center of an electromagnet is called the core • it is often made of iron

22. Electromagnets • as long as current is flowing, an electromagnet has a magnetic field • when current is turned off, there is no longer a magnetic field

23. Electromagnets • there are two ways to make an electromagnet stronger • increasing the number of coils • increasing the amount of current

24. A Simple Electromagnet:

25. Electromagnets • electromagnets are useful because they can be turned on and off • electromagnets have many important uses • ex. radios, telephones, computers

26. Electromagnets • changing the direction of an electric current causes the poles of an electromagnet to reverse • this feature is important in the production of electric motors

27. Transformers • transformer – device in which alternating current in one coil of wire induces a current in a second coil

28. Transformers • a transformer consists of two coils of wire around a magnet • the first coil, called the primary coil, is connected to the power source • the second coil, called the secondary coil, is connected to the load • a load is something that uses electricity, such as a light bulb or a motor

29. Transformers • a transformer only works with alternating current

30. Transformers • a step-up transformer increases voltage • it consists of more coils of wire in the secondary coil than the primary coil

31. Transformers • a step-down transformer decreases voltage • it consists of more coils of wire in the primary coil than the secondary coil

32. Electric Motors • electric motor – device that changes electrical energy into mechanical energy

33. Electric Motors • an electric motor is made up of an electromagnet and a permanent magnet

34. Electric Motors • the electromagnet is free to turn and is hooked up to a source of alternating current • changing the direction of an electric current causes the poles of an electromagnet to reverse

35. Electric Motors • attraction and repulsion between the electromagnet and the permanent magnet cause the electromagnet to spin

36. Generators • generator – device that changes mechanical energy into electrical energy • a current can be induced in a loop of wire by spinning the loop inside a magnetic field • due to the changing direction of the wire, an alternating current is produced

37. Generators • an electric generator is made up of an insulated loop of wire and a U-shaped magnet • spinning the loop of wire in the magnetic field of the magnet produces an electric current

38. Generators • most of the energy we use every day comes from generators

39. Generators • mechanical energy for many generators is supplied by turbines • a turbine is a large wheel that is turned by moving steam or water