1. 22.1 What is a magnet?
If a material is magnetic, it has the ability to exert forces on magnets or other magnetic materials.
A permanent magnet is a material that keeps its magnetic properties even when it is NOT close to other magnets.

2. 22.1 Properties of Magnets Magnets have two opposite poles. north
south
Magnets exert forces on each other.
The forces depend on the alignment of the poles.

3. 22.1 The force between two magnets
The strength of the force between magnets depends on the distance between them.
The magnetic force decreases with distance much faster than does either gravity or the electric force.

4. 22.1 The force between two magnets
Two magnets near each other often feel a twisting force, or torque.
This is a result of having two poles.
The combination of attractive and repulsive forces on the same magnet creates a torque.

5. 22.1 The magnetic field
All magnets create a magnetic field in the space around them, and the magnetic field creates forces on other magnets.
The number of field lines in a certain area indicates the relative strength of the magnetic field in that area. The
closer the lines are together, the stronger the field. The arrows on the field lines
indicate the direction of the force

6. 22.1 The magnetic field
The number of field lines in a certain area indicates the relative strength of the magnetic field in that area.
The arrows on the field lines indicate the direction of the force.
The closer the lines are together, the stronger the field.
Magnetic field lines always point away from a magnet’s north pole and toward its south pole.

7. 22.2 Magnetic Properties of Materials
The sources of nearly all magnetic effects in matter are the electrons in atoms.
There are two ways in which electrons create magnetism:
Electrons around the nucleus and their motion makes the entire atom a small magnet.
Electrons themselves act as though they were magnets.

8. 22.2 Magnetic Properties of Materials
In diamagnetic materials, the electrons are oriented so their individual magnetic fields cancel each other out.
Individual atoms in paramagnetic materials are magnetic but the atoms themselves are randomly arranged so the overall magnetism of a sample is zero.
When paramagnetic materials are placed in a magnetic field, the atoms align so that the material is weakly magnetic.

9. 22.2 Magnetic Properties of Materials
A small group of metals have very strong magnetic properties, including iron, nickel, and cobalt.
These metals are the best known examples of ferromagnetic materials.
Atoms with similar magnetic orientations line up with neighboring atoms in groups called magnetic domains.

10. 22.2 Magnetic Properties of Materials
Magnetic domains in a ferromagnetic material will always orient themselves to attract a permanent magnet.
If a north pole approaches, domains grow that have south poles facing out.
If a south pole approaches, domains grow that have north poles facing out.

12. 22.2 Properties of magnets
Materials that make good permanent magnets are called hard magnets.
Steel, which contains iron and carbon, is a common and inexpensive material used to create hard magnets.
Materials that lose their magnetism quickly are called soft magnets.

13. 22.3 The Magnetic Field of the Earth
As early as 500 B.C. people discovered that some naturally occurring materials— such as lodestone and magnetite—have magnetic properties.
By 1200, explorers from Italy were using a compass to guide ocean voyages beyond the sight of land.

14. 22.3 The Magnetic Field of the Earth
When you use a compass, the north-pointing end of the needle points toward a spot near (but not exactly at) the Earth’s geographic north pole.
The Earth’s magnetic poles are defined by the planet’s magnetic field.
That means the south magnetic pole of the planet is near the north geographic pole.

16. 22.3 The Magnetic Field of the Earth
The gauss is a unit used to measure the strength of a magnetic field.
The magnetic field of the Earth is very weak (0.5 gauss) compared with the strength of the field on the surface of the classroom ceramic magnets (1000 gauss).
Historical data shows that both the strength of the Earth’s magnetic field and the location of the north and south magnetic poles can switch places.
Today, the Earth’s magnetic field is losing approximately 7 percent of its strength every 100 years.

17. Units for Magnetic Fields
Tesla (T): one Newton of force per meter of wire with one amp of current
T = N/(Am)
Gauss = T

18. 22.3 The Magnetic Field of the Earth
Depending on where you are, a compass will point slightly east or west of true north.
The difference between the direction a compass points and the direction of true north is called magnetic declination.
After correcting for the declination, you rotate the whole compass until the north-pointing end of the needle lines up with zero degrees on the ring.
The large arrow points in the direction you want to go.

19. Application: Magnetic Resonance Imaging

20. What causes Earth’s Magnetic field?
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