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Like poles repel Unlike poles (opposites) attract!

What is Magnetism? Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.

What is a magnetic field? A magnetic field is the space around a magnet in which a magnetic force is exerted.

lodestone A lodestone is a “leading stone.” One end points north. compass The Chinese invented the compass by suspending a lode stone on a string.

All magnetic phenomena result from forces between electric charges in motion.

The ends of a magnet are where the magnetic effect is the strongest. These are called “poles.” Each magnet has 2 poles – 1 north, 1 south.

Poles of a magnet always Come in pairs!

Poles of a magnet N pole North-seeking It seeks geographic north. S pole South-seeking It seeks geographic south.

What is a compass? A compass is a magnet that is free to move It responds to the Earth’s magnetic field

William Gilbert, an English physician, first proposed in 1600 that the earth itself is a magnet, and he predicted that the Earth would be found to have magnetic poles.

The Earth is a magnet: It exerts magnetic forces and is surrounded by a magnetic field that is strongest near the North and South magnetic poles South magnetic poleNorth geographic pole

Magnetic poles of the earth The south pole of the earth’s magnetic field is located close to the north geographic pole. The N pole of a compass needle is attracted to the earth’s south magnetic pole. Magnetic South Pole Magnetic North Pole

What is magnetic declination? Magnetic declination is the difference between magnetic and geographic poles. It measures the angle between them.

Demo – Which objects are magnetic? We are going to try out several different objects to see if they are magnetic or not. Fill in the table in your note-taking guide with the answers. We will not be testing a razor blade or zinc.

What are ferromagnetic elements? Materials that are strongly attracted to magnets Can become temporarily magnetized The most common are Fe (iron), Co (cobalt), and Ni (nickel).

Why aren’t all nails magnetic? Nails are only magnetic if their domains are aligned properly.

What are domains? Domains are large groups of ferromagnetic atoms whose magnetic fields are aligned (lined up in the same direction). The domains are randomly oriented in unmagnetized substances. The domains align themselves with an external magnetic field (magnetic induction).

 Atoms themselves have magnetic properties due to the spin of the atom’s electrons.  These areas of atoms are called “domains”  Groups of atoms join so that their magnetic fields are all going in the same direction

When an unmagnetized substance is placed in a magnetic field, the substance can become magnetized. This happens when the spinning electrons line up in the same direction.

An unmagnetized substance looks like this…

While a magnetized substance Looks like this… Iron Lodestone (Magnetite)

Hard ferromagnetic materials (alloys) make better permanent magnets than soft iron because their domains are harder to turn.

How to break a magnet: 1. Drop it 2. Heat it This causes the domains to become random again!

If you break a magnet in half, you get 2 magnets! SNSNSN

No Monopoles Allowed It has not been shown to be possible to end up with a single North pole or a single South pole, which is a monopole ("mono" means one or single, thus one pole). Note: Some theorists believe that magnetic monopoles may have been made in the early Universe. So far, none have been detected. SN

1. Breaking a magnet in two a. destroys its magnetic properties b. makes two smaller magnets 2. Which of these actions will NOT demagnetize a magnet? a. dropping it b. heating it c. breaking it in half d. none of these

Magnetic Fields The region where the magnetic forces act is called the “magnetic field”

Direction of magnetic field lines -Magnetic field lines always start at north pole and head towards south pole. -Magnetic field lines are defined as the direction the north pole of a compass points in a magnetic field.

Field Lines Around a Bar Magnet

Field Lines Around a Magnetic Sphere

Field Lines of Repelling Bars

Field Lines of Attracting Bars

Field lines for horseshoe magnet

What is the advantage of using a horseshoe magnet? The poles are closer together on a horseshoe magnet, so both poles can be used at the same time to pick up the same object. It doubles the pickup power.

Mapping a magnetic field

Vocabulary Magnet: material that can both attract and repel other magnets. Iron is most common.Magnet: material that can both attract and repel other magnets. Iron is most common. Pole: Part of the magnet where the force is the strongestPole: Part of the magnet where the force is the strongest Metal: material that is often attracted to magnets and a good electrical conductorMetal: material that is often attracted to magnets and a good electrical conductor Horseshoe magnet:Horseshoe magnet: U-shaped magnetU-shaped magnet NS

We use the Earth’s magnetic field to find direction. The needle of a compass always points toward the magnetic south pole. We call this direction “North” (remember, opposites attract)

Vocabulary n Geographic North pole: the north end of the axis around which the Earth rotates n Magnetic South pole: the point on the Earth to which a compass needle points (north end of compass attracted to magnetic south).

Sometimes, the Earth’s magnetic poles flip. This happens every half- million years or so. Notes on the earth’s magnetic field.

Aurora Borealis – Northern Lights High temperatures on the sun’s surface produce plasma, the fourth phase of matter consisting of charged particles. These charged particles travel throughout the solar system as solar wind. When charged particles reach the region of the earth’s outer atmosphere called the magnetosphere, their motion is controlled by the earth’s magnetic field. The charged particles are able to slip through the earth’s magnetic field at the poles and enter the atmosphere. They collide with electrons in atoms of gases like oxygen and nitrogen and transfer energy, making the electrons jump to higher energy levels. When they fall, they give off visible light of different colors.

The sun has a magnetic field, too. It extends far above the sun’s surface. Other planets in the solar system also have these magnetic fields

The Earth’s magnetic field extends far into space. It is called the “magnetosphere.” When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…

The Aurora Borealis in the Northern Hemisphere And the Aurora Australis in the Southern Hemisphere

1.Magnetic field lines are drawn a. from north to south b. from south to north c. from positive to negative d. from negative to positive 2. This diagram represents the magnetic field between a. two N poles b. two S poles c. N pole (left) and S pole (right) c. S pole (left) and N pole (right) 3. The Aurora Borealis a. originates on the sun as solar wind b. is caused by charged particles transferring energy to the atoms of gases in the atmosphere c. both of these

Electromagnetism (Add this to your notes. It is on the test) The interaction between electric charges and magnets is called electromagnetism

Top Five List 1. There are North Poles and South Poles. 2. Like poles repel, unlike poles attract. 3. Magnetic forces attract only magnetic materials. 4. Magnetic forces act at a distance. 5. While magnetized, temporary magnets act like permanent magnets. What We Will Learn About Magnetism

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Go to your lab station. Take your lab report page and something to write with. You will be rotating from station to station. There are two stations for #1 because it will take the longest to do. If you have time, you will also visit the “making a magnet” station. Return to your desk afterward with your lab. It will be turned in at the end of class.

Lab – making a temporary magnet If there is time, visit this station last. You do not need paper or pencil. You should have paperclips and magnets at each station. Watch the video that is on the next slide to find out what to do.