1. Magnetic Fields and Electromagnetic Induction
The Earth’s Shield
Magnetic Fields and Electromagnetic Induction

3. Electromagnetic Induction
All charges produce ELECTRIC FIELDS
Moving charges produce MAGNETIC FIELDS
PERPENDICULAR to the motion of the charge
Magnetic field lines

4. Making a Magnet Magnetism is a FIELD FORCE No contact required
All atoms have “some” natural of magnetism
Three strongly magnetic elements
IRON, NICKEL, COBALT

5. Electromagnetic Induction
Magnets produce magnetic fields
Moving magnets produce ELECTRIC FIELDS
PERPENDICULAR to motion of the magnet
This causes ELECTRICAL CURRENT to flow

6. Magnetic Field Lines Rules for field line directions
Outside magnet  NORTH TO SOUTH
Inside magnet  SOUTH TO NORTH

7. Magnetic Field Maps
N S

8. Magnetic Field Maps
S N
N S

9. Magnetic Field Maps S N

10. Field is strongest at point C.
Example #1
Determine the direction of the magnetic field lines at each point. Where is the field strongest? A
Field is strongest at point C.
N S B C D

11. Field is strongest at point F.
Example #2
Determine the direction of the magnetic field lines at each point. Where is the field strongest? H E
S N
N S F G
Field is strongest at point F.

12. Compass The needle of a compass is a small MAGNET
The north pole of a compass needle
… is marked with a small “N” or a prominent color
… points toward magnetic SOUTH poles.

13. Example #3 Determine the direction in which the compass will point.
S N

14. Like poles REPEL. Unlike poles ATTRACT.

15. Could you separate the poles of a bar magnet by breaking it in half
Could you separate the poles of a bar magnet by breaking it in half? Why?
No, if you break a magnet in half, you create two smaller magnets, but each still has two poles.

16. Permanent (Hard) magnet - a material that retains its magnetic properties after an external magnetic field is removed.

17. Temporary (Soft) magnet - A material that shows magnetic properties only while exposed to an external magnetic field.

18. Electromagnet - A coil of wire wound about a magnetic material, such as iron, that produces a magnetic field when current flows through the wire.

19. Polarization - the temporary alignment of the magnetic domains in a magnetic material when it is placed near a magnet.

20. Polarization - the temporary alignment of the magnetic domains in a magnetic material when it is placed near a magnet.

21. Magnetic flux (B) – a vector quantity representing the number of magnetic field lines that pass through a given area.
The magnetic field is strongest where the lines are closest together. (most concentrated at poles)
Unit - Tesla (T) = kg / s2•A

22. In
Across
Out

23. Which picture has a greater magnetic field intensity (magnetic flux)?

24. Earth’s Magnetic Field
The geographic NORTH pole of the Earth acts like the SOUTH pole of a magnet!
Convection currents in the outer iron core produce the Earth’s magnetic field

25. The Magnetosphere

27. End of – PRACTICE