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Magnetism

Magnetism. An attractive subject… March 29, 2010. Let’s start off easy…. What do we know about magnets?. Magnetic field lines. What do they look like?. How are magnets like electrical charges?. Attract and repel without touching Force fields Strength depends on the distance of separation

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Magnetism

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  1. Magnetism An attractive subject… March 29, 2010

  2. Let’s start off easy… • What do we know about magnets?

  3. Magnetic field lines • What do they look like?

  4. How are magnets like electrical charges? • Attract and repel without touching • Force fields • Strength depends on the distance of separation • Like poles repel, opposites attract.

  5. How are magnets different? • Magnetic poles cannot be isolated, charges can. • When a magnet is broken, it still have two poles.

  6. Magnetic Field Lines • Remember these?

  7. Magnetic Field Lines:

  8. Magnetism is created by moving electric charge. • Moving electrons are current. • The charge in motion creates a magnetic field!

  9. Why isn’t aluminum magnetic? • Electrons spinning in opposite directions. • The magnetic fields cancel each other • But not in some metals: • Iron, Nickel, Cobalt

  10. Domains… • Little areas (domains) have magnetic properties • Magnets occur when these line up

  11. Temporary magnets • Place iron next to a magnet • The domains line up. • Take magnet away and they go back to being random.

  12. Step on a crack… break yo’ momma’s back • What happens when you break a magnet in half? • Does it stop being a magnet?

  13. How do we magnetize an object? • Place object in a strong magnetic field. • Allow domains to line up. • Tap softly to encourage orientation. • And/or • Rub with metal with magnet.

  14. De-magnetize? • Drop it or • Heat it • Will cause the domains to become random again.

  15. Electromagnets • Current passing through a wire causes a magnetic field.

  16. A coil of wire… • The magnetic field becomes bunched • Everything points in the same direction. • You get an electromagnet!!

  17. A core of iron… • The domains of the iron align with the electro magnet • You get a stronger magnet!

  18. Lab…M from E • 2 parts: • Magnetic field around a wire • Magnetic field around a solenoid (coil of wire) • Your goal is to see if you can determine the shape of each field using small compasses

  19. Magnetism & Electricity March 31, 2010

  20. Plan of the Day • Extra credit – by tomorrow in my box • Any missed assignments? • In my hands by Thursday. • And I’m not here Wednesday after school • Homework • Electric currents and magnetic fields • Lab! • Review test

  21. So, who can tell me… • What is magnetism?

  22. Magnetic Fields around wires • If you run current through a wire… • You create a magnetic field around the wire • Raise your right hand and repeat after me…

  23. Getting loopy • What happens… • If you wrap that wire into a loop?

  24. A charged particle… • If we take a charged particle • Like an electron… • And shoot it into a magnetic field… • A force acts on it. • RHR #2 • We should all be grateful that this is the case: • Cosmic radiation

  25. Electro-magnetism? • Watch and see… • Current through a wire • In a magnetic field… • What do you see?

  26. Back to the wire… • Direction of force based on current and magnetic field! • RHR #2 • The root cause is the movement of charge in a magnetic field

  27. This is how our meters work! • Idea #1 – MAGNETIC FIELD AROUND A CURRENT CARRYING WIRE • Coil of wire and a magnetic needle

  28. Motors? • IDEA #2 – CURRENT IN A MAGNETIC FIELD CREATES A FORCE • Yes – the same concept is at work in a motor…

  29. Another look…in the opposite direction

  30. Motors: Take electrical energy and convert it to mechanical energy.

  31. Generators: Take mechanical energy and convert it to electrical energy.

  32. Lab – E from M • You’re going to explore how to create electricity from a magnet. • Generator or motor? • Open-ended lab • The more you discover • The better your grade…

  33. Magnetism & Electricity April 2, 2010

  34. Plan of the Day • Review homework and lab • Generators and Motors • Lab

  35. Electro-magnetism - review • Current through a wire • In a magnetic field… • Force acts on it • Interaction between 2 magnets!

  36. If the current is reversed… • The force pushes in the opposite direction.

  37. What is the difference… • Between a motor and • A generator?

  38. Motors: • Take electrical energy • Convert it into mechanical energy.

  39. Generators: • Take mechanical energy • Convert it to electrical energy.

  40. Motors? • Current flows through the wire… • A force acts on it • One side goes up • The other down • What has to happen at the bottom?

  41. Generator or Motor?

  42. Lab • Build a motor… • (or was it a generator???)

  43. Transformers: Robots in Disguise April 6, 2010

  44. Think back to the labs… • How about the first lab… • What did you observe? • Lab 2: • What did you do to create current in the coil? • Lab 3: • Explain to a friend how you used these ideas to create a motor.

  45. Speakers • Current is quickly reversed back and forth in a wire • Causes the coil to move and vibrate the cone. • Sends out sound waves into the air.

  46. Mechanical energy – water, wind, steam, etc.

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