# Magnets and Magnetism.

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Magnets and Magnetism

GPS S8P5. Students will recognize characteristics of gravity, electricity, and magnetism as major kinds of forces acting in nature Element S8P5.c.Investigate and explain that electric currents and magnets can exert force on each other.

EQ How are magnets made? How do magnets interact with other objects or other magnets? Why do compasses point North? What affects the strength of magnetic force?

What is a Magnet? Any material that attracts iron or things made of iron is called a magnet. Properties: Two poles Exert forces on each other Surrounded by a magnetic field

Magnetic Poles Points on a magnet that have opposite magnetic qualities. North pole – the pole of a magnet that points to the north South Pole – the opposite end of the magnet points to the south Magnetic poles always work in pairs.

Push or pull that is exerted by a magnet.
Magnetic Forces Push or pull that is exerted by a magnet.

Magnetic Fields Exists in the region around a magnet in which magnetic forces can act. Shape of magnetic fields can be shown with lines drawn from the north pole to the south pole. Activity: Take your magnets and sprinkle iron fillings around it.

The closer the lines, the stronger the magnetic fields.
Where are the lines closest? Why?

The lines around a magnet are closest together at the poles, where the magnetic force on an object is strongest.

Cause of Magnetism Depends on the materials atoms.
As electrons (negative) move around, they make a magnetic field. The atom will then have a north and south pole. Groups of atoms are in tiny areas called domains. They line up and make a magnetic field. The arrangement of domains in an object determines whether the object is magnetic.

Cutting a Magnet When you cut a magnet in half, you end up with two magnets.

Question: How can a magnet lose it magnetic properties?
Dropped, hit, placed in a strong magnetic field that is opposite to its own, or heated.

Earth as a Magnet One Giant Magnet Earth behaves as if it has a bar magnet running through its center. Poles of a Compass Needle The point of a compass needle is attracted to the south pole of a magnet. Opposite poles of magnets attract each other. South Magnetic Pole near North Geographic Pole A compass needle points north because the magnetic pole of Earth that is closest to the geographic North Pole is a magnetic south pole.

The Core of the Matter Scientists think that the Earth’s magnetic field is made by the movement of electric charges in the Earth’s core. A Magnetic Light Show Earth’s magnetic field plays a part in making auroras. An aurora is formed when charged particles from the sun hit oxygen and nitrogen atoms in the air.

Using Electromagnetism
electromagnetism—the interaction between electricity and magnetism or the production of a magnetic field by electric current. When an electric current is allowed to flow through a coil of wire, the magnetic field produced around the wire is similar to that surrounding a bar magnet.

Strength of this magnetic field could be increased by placing a material such as a piece of iron inside the wire. An electromagnet is made up of a coil of wire wrapped around an iron core.

Uses of electromagnets
Electromagnets are useful devices because their magnetism can be turned on and off. The strength of electromagnetic can be controlled in three ways:

Changing the Strength of an Electromagnet
To increase strength To Decrease Strength Increase strength of current Decrease strength of current Add more coils of wire Use fewer coils of wire Increase size of iron core Decrease size of iron core

Applications of Electromagnetism
Doorbells Two solenoids, a coil of wire that produces a magnetic field when carrying an electric current, in a doorbell allows the doorbell to work.

Magnetic Force and Electric Current An electric current can cause a compass needle to move. The needle is a small magnet. This property is useful in electric motors.

An electric motor is a device that changes electrical energy into mechanical energy. All electric motors have an armature—a loop or coil of wire that can rotate.

Electric Current from a Changing Magnetic Field
Faraday’s Experiment Michael Faraday conducted an experiment trying to get the magnetic field of the electromagnet to make an electric current in a second wire.

Success for an Instant Faraday realized that electric current in the second wire was made only when the magnetic field was changing. The process by which an electric current is made by changing a magnetic field is called electromagnetic induction. Inducing Electric Current Look at the next slide to see electromagnetic induction.

Electric Generators Alternating Current The electric current produced by the generator shown on the next slide changes direction each time the coil makes a half turn. Because the electric current changes direction, it is an alternating current. Generating Electrical Energy The energy that generators convert into electrical energy comes from different sources such as fossil fuels and nuclear energy.

Transformers A transformer increases or decreases the voltage of alternating current. Step Up, Step Down The number of loops in the primary and secondary coils of a transformer determines whether it increases or decreases the voltage. Electrical Energy for Your Home The electric current that brings electrical energy to your home is usually transformed three times.