Entry quiz

1. What is the element for today?

2. What properties do we expect?

3. What is atomic number?

9th element

FluorineAtomic symbol FAtomic number 9Atomic weight 18.998Gas, nonmetalGas: very pale yellowLiquid: bright yellowSolid: transparent, opaque

Foundations of Magnetism

Unit : Electricity and Magnetism

1 Properties of Magnets

2 Magnetic Properties of Materials

3 The Magnetic Field of the Earth

Chapter. Electric Charges and Forces

Chapter Objectives1. Describe the forces between two permanent

magnets.

2. Sketch the magnetic field of a single permanent magnet.

3. Predict the direction of the force on a magnet placed in a given magnetic field.

4. Explain why ferromagnetic materials always attract magnets of either pole.

5. Describe the theory behind why a compass works.

6. Use a compass to find the direction of true north.

Chapter Vocabulary Terms

magnet north pole south pole magnetization demagnetization magnetic field compass

magnetic field lines diamagnetic

paramagnetic ferromagnetic gauss soft magnet magnetic

declination magnetic domain hard magnet permanent

magnet

1 Properties of Magnets

Key Question:

How do magnets interact with each other?

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.

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.

Properties of Magnets

Plastics, wood, and most insulating materials are virtually transparent to magnetic forces.

Conducting metals, like aluminum, also allow magnetic forces to pass through, but may change the forces.

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.

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.

The magnetic field

All magnets create a magnetic field in the space around them, and the magnetic field creates forces on other magnets.

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.

Magnetic Properties of Materials

Key Question:

How do magnets interact with different materials?

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:

1. Electrons around the nucleus and their motion makes the entire atom a small magnet.

2. Electrons themselves act as though they were magnets.

Magnetic Properties of Materials

All atoms have electrons, so you might think that all materials should be magnetic, but there is great variability in the magnetic properties of materials.

The electrons in some atoms align to cancel out one another’s magnetic influence.

While all materials show some kind of magnetic effect, the magnetism in most materials is too weak to detect without highly sensitive instruments.

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.

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.

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.

Magnetic lab activity 4

1. Draw a map of what you see2. Find the N and S direction3. Identify the direction I tell you4. Plan to get to that place and then come back to the initial point using

compass for both ways5. Record how many steps you did. Can you tell approximately the distance

you walked?6. Record everything and make necessary conclusions

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.

The Magnetic Field of the Earth

Key Question:

How do we use Earth’s magnetic field to tell direction?

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.

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.

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.

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.

Application: Magnetic Resonance Imaging

EXIT QUIZ

1. what is 10th element?

2. what is 6th element?

3. what is 4th element?

4. what are inert gases?

5. what is another name for them?