Chapter 19 - Magnetism Chapter 19 - Magnetism and Electromagnetismand Electromagnetism

Over 2,000 years ago - an area of Over 2,000 years ago - an area of Greece known as Magnesia was Greece known as Magnesia was noted for unusual rocksnoted for unusual rocksThe rock, allowed to swing on a The rock, allowed to swing on a string always pointed the same string always pointed the same way - towards the north star way - towards the north star (leading star or load star) (leading star or load star) Magnetic rock (loadstone) contains Magnetic rock (loadstone) contains ironiron

N – north seeking poleN – north seeking pole

S – south seeking poleS – south seeking pole

Like poles repelLike poles repel

Opposite poles attractOpposite poles attract

Magnetic fields are created by a Magnetic fields are created by a moving charge.moving charge.

The spinning of an electron (like The spinning of an electron (like a top) creates a tiny magnetic field. a top) creates a tiny magnetic field.

Most electrons are paired into Most electrons are paired into orbitals and spin in opposite orbitals and spin in opposite directions so their magnetic fields directions so their magnetic fields attract.attract.

When two opposite magnetic fields When two opposite magnetic fields combine they cancel each other out. combine they cancel each other out.

Requirements for something Requirements for something to be magneticto be magnetic

– It must have unpaired electronsIt must have unpaired electrons– The unpaired electrons must spin in the The unpaired electrons must spin in the

same direction so the magnetic fields add.same direction so the magnetic fields add.

– Iron, nickel and cobalt all have unpaired Iron, nickel and cobalt all have unpaired electrons and can be magnetized.electrons and can be magnetized.

Magnetic domain – a region where the Magnetic domain – a region where the unpaired electrons spin the same unpaired electrons spin the same direction so their magnetic fields add. direction so their magnetic fields add.

In a magnetized material the domains In a magnetized material the domains are arranged in the same direction. are arranged in the same direction.

see photo of magnetic domain wallssee photo of magnetic domain walls

Iron materials can be temporary Iron materials can be temporary magnets by an imposed magnetic magnets by an imposed magnetic field.field.

In picking up paperclips with a In picking up paperclips with a magnet, the paperclips become a magnet, the paperclips become a temporary magnet.temporary magnet.

The Earth is a giant magnetThe Earth is a giant magnet

It contains molten iron and nickel at the It contains molten iron and nickel at the core. (not fully understood)core. (not fully understood)Geographic north – the point around which Geographic north – the point around which the earth rotates. (Is the north of maps)the earth rotates. (Is the north of maps)Magnetic north – the point on the earth that Magnetic north – the point on the earth that the compass points to.the compass points to.Magnetic declination – the difference in Magnetic declination – the difference in degrees between true north and magnetic degrees between true north and magnetic northnorthIt is very little (about zero) in this areaIt is very little (about zero) in this area

Van Allen Belts – two doughnut Van Allen Belts – two doughnut shaped regions far above the earth shaped regions far above the earth (1,000 to 25,000 km) that contain (1,000 to 25,000 km) that contain high speed protons and electrons high speed protons and electrons

Solar wind – a stream of electrically Solar wind – a stream of electrically charged particles that comes from the charged particles that comes from the sun.sun.

Magnetosphere – the earth’s magnetic Magnetosphere – the earth’s magnetic field as shaped by the solar wind.field as shaped by the solar wind.

Northern lights – caused by charged Northern lights – caused by charged particles from space entering the earth’s particles from space entering the earth’s magnetic field (magnetosphere)magnetic field (magnetosphere)

The earth makes magnetsThe earth makes magnets

Molten rock that contains iron becomes Molten rock that contains iron becomes magnetized by the earth as it hardens.magnetized by the earth as it hardens.

Studying ancient volcanic rock gives a Studying ancient volcanic rock gives a history of the earth’s magnetic field.history of the earth’s magnetic field.

It moves over time and even reverses It moves over time and even reverses itself every million years or so.itself every million years or so.

Electric current – a movement of Electric current – a movement of charged particles (such as charged particles (such as electrons moving through a wire)electrons moving through a wire)

A moving charge creates a A moving charge creates a magnetic field.magnetic field.

Amp – a measure of current Amp – a measure of current (electron flow per second)(electron flow per second)

Solenoid – a coil of wire that produces a Solenoid – a coil of wire that produces a magnetic field when electricity is run magnetic field when electricity is run through it. through it.

http://webphysics.davidson.edu/applets/http://webphysics.davidson.edu/applets/BField/Solenoid.htmlBField/Solenoid.html

http://www.solenoids.com/http://www.solenoids.com/

Solenoid + iron core makes an Solenoid + iron core makes an electromagneticelectromagnetic