Magnets and Magnetism

GPS

S8P5. Students will recognize S8P5. Students will recognize characteristics of gravity, electricity, characteristics of gravity, electricity, and magnetism as major kinds of and magnetism as major kinds of forces acting in natureforces acting in nature

Element S8P5.c.Element S8P5.c.Investigate and Investigate and explain that electric currents and explain that electric currents and magnets can exert force on each other.magnets can exert force on each other.

EQ

How are magnets made? How are magnets made? How do magnets interact with How do magnets interact with

other objects or other magnets? other objects or other magnets? Why do compasses point North? Why do compasses point North?

What affects the strength of What affects the strength of magnetic force? magnetic force?

What is a Magnet?

Any material that attracts iron or things Any material that attracts iron or things made of iron is called a magnet. made of iron is called a magnet.

Properties:Properties: Two polesTwo poles Exert forces on each otherExert forces on each other Surrounded by a magnetic fieldSurrounded by a magnetic field

Magnetic Poles

Points on a magnet that have opposite Points on a magnet that have opposite magnetic qualities.magnetic qualities.

North pole – the pole of a magnet that North pole – the pole of a magnet that points to the northpoints to the north

South Pole – the opposite end of the South Pole – the opposite end of the magnet points to the southmagnet points to the south

Magnetic poles always work in pairs.Magnetic poles always work in pairs.

Magnetic Forces

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

Magnetic Fields

Exists in the region around a magnet in Exists in the region around a magnet in which magnetic forces can act. which magnetic forces can act.

Shape of magnetic fields can be shown Shape of magnetic fields can be shown with lines drawn from the north pole to with lines drawn from the north pole to the south pole.the south pole.

Activity: Take your magnets and Activity: Take your magnets and sprinkle iron fillings around it.sprinkle iron fillings around it.

The closer the lines, the stronger the The closer the lines, the stronger the magnetic fields.magnetic fields.

Where are the lines closest? Why?Where are the lines closest? Why?

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

Cause of Magnetism

Depends on the materials Depends on the materials atomsatoms.. As electrons (negative) move around, they As electrons (negative) move around, they

make a magnetic field.make a magnetic field. The atom will then have a north and south pole.The atom will then have a north and south pole. Groups of atoms are in tiny areas called Groups of atoms are in tiny areas called

domainsdomains.. They line up and make a magnetic field.They line up and make a magnetic field. The arrangement of domains in an object The arrangement of domains in an object

determines whether the object is magnetic.determines whether the object is magnetic.

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

Question: How can a magnet lose it Question: How can a magnet lose it magnetic properties?magnetic properties?

Dropped, hit, placed in a strong Dropped, hit, placed in a strong magnetic field that is opposite to its magnetic field that is opposite to its own, or heated.own, or heated.

Earth as a Magnet

One Giant Magnet One Giant Magnet Earth behaves as if it has a bar Earth behaves as if it has a bar magnet running through its center.magnet running through its center.

Poles of a Compass Needle Poles of a Compass Needle The point of a The point of a compass needle is attracted to the south pole of a compass needle is attracted to the south pole of a magnet. Opposite poles of magnets attract each magnet. Opposite poles of magnets attract each other.other.

South Magnetic Pole near North Geographic Pole South Magnetic Pole near North Geographic Pole A compass needle points north because the A compass needle points north because the magnetic pole of Earth that is closest to the magnetic pole of Earth that is closest to the geographic North Pole is a magnetic geographic North Pole is a magnetic south south pole.pole.

The Core of the Matter The Core of the Matter Scientists Scientists think that the Earth’s magnetic field is think that the Earth’s magnetic field is made by the movement of electric made by the movement of electric charges in the Earth’s core.charges in the Earth’s core.

A Magnetic Light Show A Magnetic Light Show Earth’s Earth’s magnetic field plays a part in making magnetic field plays a part in making auroras. An auroras. An auroraaurora is formed when is formed when charged particles from the sun hit charged particles from the sun hit oxygen and nitrogen atoms in the air.oxygen and nitrogen atoms in the air.

Using Electromagnetism

electromagnetismelectromagnetism—the interaction —the interaction between electricity and magnetism or between electricity and magnetism or the production of a magnetic field by the production of a magnetic field by electric current.electric current.

When an electric current is allowed to When an electric current is allowed to flow through a coil of wire, the magnetic flow through a coil of wire, the magnetic field produced around the wire is similar field produced around the wire is similar to that surrounding a bar magnet.to that surrounding a bar magnet.

Strength of this magnetic field Strength of this magnetic field could be increased by placing a could be increased by placing a material such as a piece of iron material such as a piece of iron inside the wire.inside the wire.

An An electromagnetelectromagnet is made up is made up of a coil of wire wrapped around of a coil of wire wrapped around an iron core.an iron core.

Uses of electromagnets

Electromagnets are useful Electromagnets are useful devices because their devices because their magnetism can be turned on magnetism can be turned on and off. and off.

The strength of The strength of electromagnetic can be electromagnetic can be controlled in three ways:controlled in three ways:

Changing the Strength of an Electromagnet

To increase To increase strengthstrength

To Decrease To Decrease StrengthStrength

Increase strength of Increase strength of currentcurrent

Decrease strength Decrease strength of currentof current

Add more coils of Add more coils of wirewire

Use fewer coils of Use fewer coils of wirewire

Increase size of iron Increase size of iron corecore

Decrease size of Decrease size of iron coreiron core

Applications of Electromagnetism

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

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

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

Electric Current from a Changing Magnetic Field

Faraday’s ExperimentFaraday’s Experiment Michael Faraday conducted Michael Faraday conducted an experiment trying to get the magnetic field of the an experiment trying to get the magnetic field of the electromagnet to make an electric current in a electromagnet to make an electric current in a second wire.second wire.

Success for an Instant Success for an Instant Faraday Faraday realized that electric current in the realized that electric current in the second wire was made only when the second wire was made only when the magnetic field was changing. The magnetic field was changing. The process by which an electric current is process by which an electric current is made by changing a magnetic field is made by changing a magnetic field is called called electromagnetic induction. electromagnetic induction.

Inducing Electric Current Inducing Electric Current Look at the Look at the next slide to see electromagnetic next slide to see electromagnetic induction.induction.

Electric Generators

Alternating Current Alternating Current The electric current produced The electric current produced by the generator shown on the next slideby the generator shown on the next slide changes changes direction each time the coil makes a half turn. direction each time the coil makes a half turn. Because the electric current changes direction, it is Because the electric current changes direction, it is an alternating current.an alternating current.

Generating Electrical Energy Generating Electrical Energy The energy that The energy that generators convert into electrical energy comes from generators convert into electrical energy comes from different sources such as fossil fuels and nuclear different sources such as fossil fuels and nuclear energy.energy.

Transformers A A transformertransformer increases or decreases the increases or decreases the

voltage of alternating current.voltage of alternating current.

Step Up, Step DownStep Up, Step Down The number of loops The number of loops in the primary and secondary coils of a in the primary and secondary coils of a transformer determines whether it increases transformer determines whether it increases or decreases the voltage.or decreases the voltage.

Electrical Energy for Your Home Electrical Energy for Your Home The The electric current that brings electrical energy to electric current that brings electrical energy to your home is usually transformed three times.your home is usually transformed three times.