1. Chapter 2 Electromagnetism

2. Chapter 2 Bellringers Friday 9/11/09 What do you know about magnets? North and south poles North and south poles attract Like poles repel each other Bar magnets and horseshoe magnets

3. Section 2-1: Magnets and Magnetism (Pgs. 40- 46) Properties of Magnets Magnet- any material that attracts iron or things made of iron. Properties of magnets 1. All have a south and north pole 2. Exert forces on each other 3. Surrounded by magnetic field

4. Magnetic Poles A magnet’s magnetic forces are NOT the same throughout the magnet. Strongest forces are near the ends of a magnet. Each end is a magnetic pole Magnetic poles- points on a magnet that have opposite magnetic qualities.

5. North and South End of the magnet that points North is the magnet’s north pole End of the magnet that points South is the magnet’s south pole Poles always occur in pairs Never find a magnet with just a south pole or just a north pole

6. Magnetic Forces Magnetic force- attraction or repulsion created by spinning electric charges in the magnet. Forces are always present in a magnet Like poles repel each other Opposite poles attract each other

7. Magnetic Fields Magnetic field- region around a magnet’s pole in which magnetic forces act. Shape of field can be shown with lines Magnetic field lines- map the shape and strength of magnetic force on a magnet Closer the lines, stronger the force Lines closest at magnet’s poles

9. Monday 9/14/09 Name one property that all magnets have. All have a north and south pole All exert forces on each other All have magnetic fields What creates the magnetic forces in a magnet? Spinning electric charges from the electrons in the magnet’s atoms

10. Cause of Magnetism? Whether or not a material is magnetic, depends on the material ’ s atoms An atom ’ s moving electrons cause magnetism As electrons move, it creates a magnetic field around the atom Each atom becomes like a tiny magnet

11. Materials that are magnetic have their atoms lined up in domains Domains- groups of atoms in small areas Arrangement of domains determines whether an object is magnetic North and south poles of all the atoms in a domain line up Material is then magnetized If poles do not line up, magnetic fields of all the atoms cancel out, and material is not magnetized

13. Losing Alignment Magnets domains can move, making the magnet demagnetized Domains can move by: 1. Dropping a magnet 2. Putting magnet in an opposite magnetic field 3. Increasing temperature Higher temps cause atoms to vibrate faster causing them not to be lined up

14. Making a magnet Item must have domains that move Examples: iron, nickel, and cobalt Rub one pole of a magnet in one direction on the item Item ’ s domains become aligned with magnetic field of the magnet Since domains are aligned, the item is magnetized

15. What can be picked up by a magnet? Anything that will allow it’s domains to move Example: paper clip Bring magnet close to paper clip Magnet’s magnetic field causes paper clip’s domains to align – causes paper clip to become temporary magnet Paper clip’s north pole will attract to magnet’s south pole and vice versa

16. Tuesday 9/15/09 What must atoms do in order for an item to be magnetic? Atoms must line up their north and south poles Name three things that can demagnetize a magnet? Drop it Put it in an opposite magnetic field Increase the temperature

17. Cutting a magnet End up with two separate magnets Each piece has a north and south pole REMEMBER Properties of Magnets 1. All have a south and north pole

18. Kinds of magnets 1. Ferromagnets - are made of iron, nickel, or cobalt 2. Electromagnets - are made by electric current 3. Temporary magnets – easy to magnetize, but lose magnetism quickly 4. Permanent magnets – difficult to magnetize, but keep magnetism longer

19. Earth as a Magnet William Gilbert suggested Earth was a giant magnet. Earth’s magnetic poles are near the geological poles Magnetic south is in geological north In order for a magnet’s north pole to point geological north, it must be attracted to a magnetic south Magnetic north is in geological south

21. Why Earth is magnetic? There is NO bar magnet in the Earth Earth’s magnetic field is created by electric charges that exist in the Earth’s core Outer core is liquid iron and cobalt and moves as Earth rotates. As a result, electric charges also rotate creating a magnetic field

22. Magnetic Light Show Aurora – beautiful display of lights that appear in the sky above the poles Formed when charged particles from the sun hit oxygen & nitrogen atoms in the air Earth’s magnetic field blocks charged particles from the sun

24. Earth’s Magnetic Field

25. So why are auroras seen at poles? Earth’s magnetic field bends in at the poles Charged particles able to enter the atmosphere near the poles Northern lights (aurora borealis) appear at north pole Southern lights (aurora australis) appear at south pole

26. Section 2-2 Magnetism from Electricity Discovery of Electromagnetism Discovered by Hans Christian Oersted Held a compass near a wire carrying an electric current Compass needle did not point north Only thing that can cause this is another magnetic field Oersted concluded that electric current produces a magnetic field

27. Also found that the direction of the magnetic field depended on direction of the current. Run current one direction, compass needles turn in a clockwise direction Run current the other direction, compass needles turn counterclockwise direction Electromagnetism – the interaction between electricity and magnetism

28. Thursday 9/17/09 How did Oersted discover that electric current produces a magnetic field? Held a compass near a current carrying wire and compass did not point North What determines the direction of a magnetic field in a current carrying wire? The direction of the current

29. Using Electromagnetism Magnetic field generated by an electric current is weak. Solenoids and electromagnets strengthen this magnetic field Maglev (magnetic levitation) trains are pulled down the track by an electromagnet

31. Solenoids Solenoid- coil of wire that produces a magnetic field when carrying electric current. Magnetic field produced by a solenoid can be increased two ways 1. Increase the numbers of loops in the solenoid 2. Increase the current running through the wire

32. Electromagnets Electromagnet- a solenoid wrapped around an iron rod. Magnetic field of the solenoid makes the atoms in the iron line up. Both the solenoid and the iron now have a magnetic field The two magnetic fields combine to create a strong magnetic field for the electromagnet

33. Magnetic field of an electromagnet can be made even stronger Same ways as a solenoid 1. Increase the number of loops in the solenoid 2. Increase the current running through the solenoid

34. Turning Electromagnets On and Off Solenoid only has magnetic field if electric current is in the wire Turn on current, solenoid has a magnetic field and the iron also has a magnetic field Turn off current, magnetic field is no longer present and iron is not magnetic

35. What is a coil of wire with an electric current? Solenoid What do we add to a solenoid to make it an electromagnet? Iron What two things increase the magnetic fields of solenoids and electromagnets? Increase number of loops Increase current

36. Applications of Electromagnetism A current carrying wire can cause a compass needle to move If a current carrying wire can cause a magnet to move, can a magnet cause a current carrying wire to move? Yes, and this is useful in electric motors

37. Electric Motors Electric Motors - device that changes electrical energy into mechanical energy. All have a loop of wire that can rotate Located between the poles of a permanent magnet

38. Loop of wire is attached to a battery Wire now has a current running through it so it also has a magnetic field Since it is in between the poles of a permanent magnet, the permanent magnet pulls on the loop of wire and rotates it

39. Galvanometers Galvanometers- uses an electromagnet to measure electric current Has electromagnet placed between poles of a permanent magnet Electromagnet also attached to a needle When current runs through, electromagnet turns on and is pulled by permanent magnet moving needle

41. Section 2-3 Electricity from Magnetism (Pgs. 54-59) Electric Current from a Changing Magnetic Field Oersted discovered that an electric current could produce a magnetic field. If an electric current can produce a magnetic field, can a magnetic field produce an electric current? Michael Faraday’s experiments answer this question

42. Faraday’s Experiment Wrapped a wire attached to a battery around an iron ring creating an electromagnet Wrapped a second wire around the other side of the ring and attached it to a Galvanometer. Galvanometer measured no electric current in the second wire Would appear magnetism cannot create an electric current, until Faraday discovered something.

43. Faraday’s Discovery The instant he connected or disconnected the wire to the battery, the galvanometer pointer moved. As long as battery was fully connected, no electric current was measured by the galvanometer. Electric current is ONLY made when magnetic field is changing. Electromagnetic Induction- the process by which an electric current is made by changing a magnetic field.

44. Inducing Electric Current Move either the wires or the magnet Move a magnet through the loops of a wire Move a wire between the poles of a magnet Either way, magnetic field is changing and electric current is produced in the wires. Charges in a wire only move when they pass through a magnetic field.

45. How to increase the electric current 1. Move magnet through the loops faster 2. Add more loops to the wire 3. Move wire faster between the poles of the magnet

46. Wednesday 9/23/09 In order for a magnetic field to produce an electric current, what must happen? Magnetic field must be changing What can you do to increase the current produced by a magnetic field. Move the magnet or wires faster Add more loops of wire

47. Electric Generators Electric Generator- uses electromagnetic induction to change mechanical energy into electrical energy A wire sits between the poles of a permanent magnet. A crank turns the wire. Because the wire keeps moving through the magnetic field, a current is produced in the wire.

48. Generators Produce Alternating current Every half turn, the wire crosses the magnetic field in a different direction Current goes opposite direction As a result, the electric current produced is an alternating current Alternating current MUST be produced in order for transformers to work.

49. Power Plant Generators Use many coils of wire instead of one Rotate magnets around the wire instead of rotating wire inside of the magnet Use many sources to turn the turbines that turn the magnets 1. Steam from nuclear reactions 2. Water 3. Wind

50. Transformers Transformers- increases or decreases the voltage of alternating current. Two separate coils of wire wrapped around an iron ring Primary (first) coil receives an alternating current from the generator Current produces a magnetic field in the iron ring

51. Because current is alternating, magnetic field of iron ring is constantly changing direction. That changing magnetic field allows an electric current to be produced in the secondary (second) wire. If current was not alternating, no current would be produced in second wire.

52. Thursday 9/24/09 What type of current do generators produce? Alternating current What increases and decreases the voltage of alternating current? Transformers

53. Step-Up, Step-Down Number of loops in primary and secondary coils determines whether voltage is increased or decreased. Step-up Transformer- increases the voltage and decreases current More loops in secondary coil causing voltage to increase

54. Step-Down Transformers – decreases voltage and increases current Less loops in the secondary coil causes voltage to decrease Amount of power (W) stays constant Power = current (I) x voltage (V) So if voltage goes down, current must go up and visa versa.

55. Why Increase and Decrease Voltage? Voltage must be increased after leaving power plant in order to travel long distances on power lines Voltage is stepped down before it enters your house to keep appliances from blowing up