1. Bell Ringer
Give an example of something that you observed over break which involved physics.
Be sure to thoroughly explain your answer.

2. Magnetism

3. Magnetism
Force of attraction or repulsion cause by the movement of charged participles
It is not charge
It is caused by the movement of charge

4. Magnetic Poles
Magnetic Poles: A region on a magnet which produces magnetic forces
The poles of a suspended magnet will align themselves to the poles of the Earth
Fundamental Rule: Like poles repel; opposite poles attract

5. Magnetic Poles
Magnetic poles behave similarly to electric charges EXCEPT:
Electric charges can be isolated
Magnetic poles cannot

6. Magnetic Fields
Magnetic Field: The space around a magnet in which a magnetic force is exerted
The shape of a magnetic field is revealed by magnetic field lines
Directed away from north poles and toward south poles
The strength of magnetic fields are measured in units of Tesla (T)

7. Magnetic Fields

8. Magnetic Fields

9. Magnetic Fields
Magnetic fields are caused by the motion of electric charges
Since motion is relative, so are magnetic fields
Magnets at rest consist of charges in motion
Every spinning electron is a tiny magnet
Electrons spinning in the same direction produce a stronger magnet

10. Magnetic Domains
Magnetic Domain: Clusters of aligned atoms

11. Magnetic Domains

12. Bell Ringer
1.) Draw the magnetic field lines for a bar magnet with its North Pole on the bottom and its south pole on top.
2.) How are the domains arranged in a permanent magnet?

13. Magnetic Domains
If the magnetic domains of a material can align, this material is called ferromagnetic.

14. Magnetic Domains
Permanent magnets are made by placing materials in strong magnetic fields
Aligns the domains
It is possible to weaken a magnet by dropping or heating it
Pushes the domains out of alignment

15. Earth’s Magnetic Field
Currents in the molten part of Earth beneath the crust create the Earth’s magnetic field
Moving charges loop within the Earth
Earth’s magnetic field is not stable
Magnetic pole and geographic pole are offset

16. Earth’s Magnetic Field
Magnetic poles are located:
North: Hudson Bay region of northern Canada (1800 km from geographic pole)
South: Just south of Australia
Magnetic Declination: Difference between geographic and magnetic poles

17. Bell Ringer 5/13
From what was discussed in yesterday’s class…what do you believe the true name of our school should be?

18. Earth’s Magnetic Field

19. Earth’s Magnetic Field
The magnetic field of Earth reverses on an irregular cycle
1 million years ago, the field completely “shut off” for 10,000-20,000 years
Its strength has decreased by 5% over the last 100 years
Indicates a reversal possibly in the next 200 years

20. Earth’s Magnetic Field

21. Earth’s Magnetic Field
Courtesy of NASA, JPL and GSFC

22. Electric Current
Recall: Electric current is the movement of electric charges
Current produces a magnetic field
When current is carried through a conductor, the magnetic field produces a pattern of concentric circles

23. Electric Current This concept is known as Oersted’s Principle
If the current switches direction, the compass needles will turn 180o

24. Electromagnets If a current carrying wire is bent into a loop:
Field lines become bunched inside the loop
Two overlapping loops:
Twice the concentration of magnetic field lines

25. Electromagnets

26. Electromagnets

27. Electromagnets
Electromagnet: A current-carrying coil of wire with many loops
The magnetic domains of a piece of iron placed in the coil will be aligned
The will intensify the magnetic field
The strongest electromagnets use superconductors as a core

28. Electromagnet Applications
An alarm bell uses an electromagnet with a changing magnetic field to move a plunger

29. Junkyardpickerupper

30. Bell Ringer
How does a speaker work?

31. Moving Particles
A moving charged particle could be deflected by a magnetic field
For particles moving parallel to the magnetic field, no deflection occurs
For particles moving perpendicular to the magnetic field, maximum deflection occurs

32. Moving Particles

33. Moving Particles
A current carrying wire will also be deflected when it encounters a magnetic field
The particles trapped inside the wire are deflected, therefore pushing the wire itself
If the direction of the current is reversed, the deflecting force acts in the opposite direction

34. Moving Particles

35. Applications
The follow items use the idea
TVs
MRIs
Aurora Borealis

36. Bell Ringer
When will a charged particle experience the maximum amount of force when entering a magnetic field?

37. Motors
A simple DC motor uses a permanent magnet to establish a field where an electromagnet is made to rotate
When connected to a battery, the electro-magnet will rotate one half turn
Its south pole will align with the north pole of the permanent magnet

38. Motors

39. Motors Brushes Commutator
These two devices change the direction of the current at exactly the correct moment so that the poles of the electromagnet reverse
This causes the electromagnet to keep spinning
Brushes
Commutator

40. Motors
As the armature passes through the horizontal position, the poles of the electromagnet reverse due to the commutator

41. Bell Ringer
Where the motors that you made last week operating on alternating or direct current?
What would happen with your motor from yesterday if you took off all the insulation off of each end?

42. Meters
Galvanometer: A sensitive instrument used to detect electric current
Consists of a magnetic needle centered under loops of insulated wire
Electric current will cause the needle to pivot, detecting even very small currents
May be calibrated to measure current (ammeter) or voltage (voltmeter)

43. Meters