Magnetism: a force of attraction or repulsion by magnetic materials. Copper, plastic, and glass attracted to magnets.

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1 Discuss What is a Magnet? Magnetism: a force of attraction or repulsion by magnetic materials. Copper, plastic, and glass attracted to magnets. Steel, iron, and nickel attracted to magnets. o These materials are said to be. Pole: the ends of a magnet where the forces are strongest. Every magnet has poles: a pole and a pole. If a magnet is broken into pieces, each piece will still have poles. Poles behave similarly to electric charges. Opposites and likes. A north and a south will. Two north poles will. Two south poles will. Why are they called North and South Poles? If a bar magnet is suspended by a piece of string, it will act like a compass. The side that points north is said to be north-seeking and is called the north pole. The side that points south is said to be south-seeking and is called the south pole. The used this to assist in navigating ships in the twelfth century. ARE NOT 2 NORTH SOUTH ATTRACT CHINESE ATTRACT REPEL REPEL FERROMAGNETIC REPEL 2

2 Magnetic Field Lines Magnetic Field Lines: the region of magnetic force around a magnet. It causes attraction between the magnet and another object. A magnetic field is made up of. These lines of force will show the of a magnetic field. Magnetic lines of force begin at the and end at the south pole. They are closest together at the, where the field is the strongest. magnetic field lines of force direction poles north N S N S Magnetic lines of force from the South and North poles will bend torwards each other.

3 Magnetic lines of force from two South poles or two North poles will bend away from each other. N S S N What causes magnetism? Magnetism is related to. o A charge which is at rest is surrounded by and field (as well as a gravitational field). o A moving charge is surround by both an and a field. So, moving charges cause magnetic fields. Where are the moving charges in a bar magnet? Bar magnets are made of. Atoms are made of charged particles. electric o The in an atom are always moving and form a tiny current. charges in motion atoms electrons spin electric electric o Electrons on their own axis (like a top). This is more important than the magnetic field due to orbital motion.

4 o Most materials cannot be magnets. In most materials, the electrons spin in directions. o The electron spins do not cause the field be cancelled in,, and. Magnetic Domains: groups of atoms whose magnetic poles line up in the same direction. When materials are magnetized, the magnetic domains point in the same different (random) nickel direction cobalt iron different When materials are NOT magnetized, the domains point in directions. Not Magnetized Magnetized Domains NOT Aligned Domains Aligned

5 How Can You Make A Magnet? Magnetic Induction: the process by which a material can be made into a magnet. Materials can be magnetized by being rubbed in direction with a magnet. Materials become magnetized when the point in the same direction. Not all materials respond in the same way to the magnetic field. Natural Magnets: magnets that occur in Temporary Magnets: Magnets that are magnetized easily but lose the magnetism easily as well. Permanent Magnets: Magnets that are difficult to magnetize but they keep the magnetism well. loose domains nature same All magnets can their magnetism. Dropping, hitting or heating the magnet can demagnetize it because the domains become unaligned. How is Earth like a Magnet? A British scientist named Wilbert Gilbert suggested that Earth is a magnet when he observed a magnet hanging from a string will align its north and south poles with the north and south poles of the Earth. The Earth s Magnetic Poles 2 Earth has magnetic poles. close the same Magnetic poles are, but not the geographic poles. What we call the Earth s north pole is actually the magnetic pole. What we call the Earth s south pole is actually the magnetic pole. When a compass points north its is because the compass s north pole is attracted to the Earth s magnetic south pole, which we call the north pole. south norht

6 The Magnetosphere: the magnetic field around the Earth. The magnetosphere traps some charged particles from the sun that interact with other particles in the atmosphere, causing the air above Earth to glow. This is called an aurora.

7 How are electricity and magnetism related? Oersted s Discovery The relationship between electricity and magnetism is called electromagnetism. Hans Christian Oersted noticed that when current flowed through a wire, a nearby compass move pointer. He discovered that an electric current produces a magnetic field. Electromagnetic Induction: Does a magnetic field produce an electric current? Michael Faraday brought a strong magnet near a still wire. o If the magnet remains stationary, then current does not flow through the wire. o If the magnet moves toward or away from the wire continuously, then current will flow through the wire. o If a coil of wire moves toward or away from a magnet, then current will flow through the wire. The process by which an electric current is produced in a wire when the wire is exposed to a induction changing magnetic field is called. o The changing magnetic field is often changing due to relative movement. The wire and the magnet need to move relative to each other.

8 What is an electromagnet? A wire carrying an electric current always has a field around it. o The field around a straight wire is very weak. o However, if the wire is wound into a coil, the magnetic field becomes much. An electromagnet is a magnet made by wrapping a current-carrying wire around a metal. It is called temporary because when the current is turned off, there is no longer a magnetic field. Increasing the strength of the electromagnet: There are three major ways to increase the strength of the electromagnet: o Increase the number of. o Increase the amount of. o Adding a metal. What is an electric motor? magnetic stronger An electric motor converts energy into mechanical temporary nail nail coils current energy. magnetic electromagnetic Rotation is created by alternating between attraction and repulsion between a current carrying wire and a permanent magnet.

9 Analyze: Please use the notes from our class discussion and your book in order to explain all of your observations. YOU MUST USE COMPLETE SENTENCES. Station 1: Levitation Explain, using what you have learned about magnets, how we can levitate one magnet above another. Be sure to include a comparison of the strength of the necessary magnetic force with the strength of the gravitational force. A magnetic force appears between two like poles of a magnet. The magnetic force depends on the distance (less distance, more force) at a point the magnetic repulsion equals the gravitational pull from earth. At this point the magnets seem to levitate en top of each other. Station 2: Love-Hate A north pole is attracted to a pole. A south pole is attracted to a pole. north A north pole repels a pole. south south north A south pole repels a pole. Station 3: Attractiveness Are all metals attracted to a magnet? no List three materials that are attracted to a magnet: Iron (steel is iron with carbon) o nickel o cobalt o

10 Station 4: Make-a-Compass Explain in a few sentences, using your own words, how you were able to magnetize the pin in order to make your compass. You rubbed it against the compass in the same direction a lot of times Explain in a few sentences, using your own words, how you can use a compass to find your way. The needle in the compass always points north. By rotating the compass so it aligns with the needle we can also find the other directions Can a compass be used in the Southern Hemisphere? If yes, how? If no, why not? Yes, a compass can be used in the Southern Hemisphere. The whole planet acts like a magnet with a north and a south pole. The compass needle will still be attracted to the south pole. Station 6: Building an Electromagnet Fill in the Blanks: o The current carrying coil is surrounded by a strong magnetic field. o The strong magnetic field aligns the domains in the nail. o The nail is now a. magnet