1. Fields 4: Magnetism

2. N S What is Magnetism? Another force that exists around moving charged objects. e N S

3. What is a Magnet? A material in which the spinning electrons of its atoms align with one another.

4. What are ferromagnetic materials? Permanent magnets are made of ferromagnetic material such as Iron, Nickel, Cobalt, or an alloy of Al, Ni, or Co When a magnet is placed near a metallic object: Pairs of spinning electrons align temporarily to induce a magnetic field.

5. What if we cut a magnet?

6. How do like and unlike poles interact with each other? Has two ends called poles (where the magnetic force is the strongest.) Like poles repel, unlike poles attract. Lines of force emerge from a North pole, curve around the magnet and go into the south pole.

7. Earth is like a giant magnet Moving charged particles in the molten core generate a magnetic field. Can be detected using a compass, which aligns itself with the Earth’s magnetic field.

8. Earth is like a giant magnet Moving charges particles in the molten core generate a magnetic field.

11. How are magnetic fields similar to gravitational and electric fields? It’s a field – objects in the area around magnet experience a force without the need to touch. Like an E-field –It has polarity with attractive and repulsive forces (grav. fields are only attractive.) –Exerts a force on a moving charge.

12. Representing Magnetic Fields Imaginary lines that map out a magnetic field around a magnet. Also known as Magnetic Flux Lines Always form closed loops and never cross. Emerge from N-Pole and enter S-Pole.

13. Magnetic Field Strength The number of magnetic lines of flux per unit area passing through a plane perpendicular to the direction of the lines.

14. The density of field lines –B–Bunched = stronger field –S–Spread out = weaker field Vector quantity –M–Magnitude –D–Direction

15. Vector quantity –Magnitude –Direction

16. Sketching Magnetic Fields

17. Magnetic Fields and Conductors

18. Moving electrons in a conductor produce magnetic fields How can we describe these fields?

19. Magnetic field around a straight conductor Definitions: X = into the page.  = out of the page. X X   x x x x         X 

20. Magnetic field around a straight conductor First Left Hand Rule: Thumb: direction of current flow. Fingers: direction of magnetic field.

21. Magnetic field around a coil of wire Second Left Hand Rule: Fingers: Wrap around the coil in the direction of current. Thumb: Point in the direction of North.

22. N S

23. Electromagnet

24. Force on a conductor in a magnetic field Fields on top add, while fields on bottom cancel Higher field strength on top, so conductor moves down.

25. Force on a conductor in a magnetic field Current (I) Field (B) Force (F) Third Left Hand Rule: (FBI) Thumb: Direction of Current (I) Pointer: Direction of Mag. field (B) Middle Finger: Direction of Force (F)

26. Force on a conductor in a magnetic field Third Left Hand Rule: (FBI) Thumb: Direction of Current (I) Pointer: Direction of Mag. Field (B) Middle Finger: Direction of Force (F) x  NSNS