1. Magnetic Fields
Chapter 24

2. Magnetism
Since ancient times, certain materials, called magnets, have been known to have the property of attracting tiny pieces of metal. This attractive property is called magnetism. N S
Bar Magnet N S

3. Magnetism
The strength of a magnet is concentrated at the ends, called north and south “poles” of the magnet.

4. Any magnet cut in half will become two independent magnets
Magnets are always Dipoles (two poles), magnetic Monopoles (either just north or south) have never been found

5. Magnetic Poles Like poles repel ( N repels N and S repels S)
Opposite poles attract (N attracted to S)

6. Newton’s 3rd Law and Magnetic Field Strength
Two interacting magnets will put an equal force on each other
Even if one is a stronger magnet than the other

7. Magnetic Field Diagrams
Similar to electric field diagrams
What similarities do you see?

8. Magnetic Field Diagrams
North = outwards arrows (just like positive particles)
South = inwards arrows (just like negative particles)
Magnetic fields created by a bar magnet interacting with itself:

9. Magnetic Field Diagrams: Attraction
Magnetic attraction diagrams look similar to particle attractions

10. Magnetic Field Diagrams: Repulsion
Magnetic repulsion diagrams look similar to particle repulsions

11. Magnetic Field Diagrams: Strength
Denser lines = stronger magnetic field
Always strongest at the poles of a magnet

12. Charged Particles and Magnets
Charged particles experience an electric force when in an electric field regardless of whether they are moving or not moving
There is another force that charged particles can experience even in the absence of an electric field but only when they are motion
Magnetic Interactions are the result of relative motion
***In other words: In order for a charged particle to feel the force of a magnetic field, it must be moving.

13. How Compasses Work
Why does a compass point North? The red/north end is always attracted to the south magnetic pole of the Earth (which is the geographical north pole)

14. Practice Which of the below shows: Repulsion Attraction
Bar Magnet interacting with itself

15. Practice At which point is the magnetic field the weakest?
At which point is the magnetic field the strongest?

16. Practice
Determine what, if anything, is wrong with the situation presented below. If something is wrong, identify it and explain how to correct it. If nothing is wrong, explain why the situation is correct:
A stationary positively charged particle placed at the position shown in the figure below will start moving to the left because it will be repelled by the N pole of the magnet.
The statement is incorrect.
A positively charged particle placed at the position in the figure would not feel any magnetic force unless it was moving and hence would not move at all.