Magnets

Properties of Magnets•A magnet is any material that attracts iron and materials that contain iron.

•Magnets attract or repel other magnets.

•One part of a magnet will always point north when allowed to swing freely

•Magnets will point towards the North Star or Polaris, also known as the leading star, or lodestar.

Magnetic Poles•A magnetic pole is the end of a magnet

•North pole: end that points North

•South pole: opposite end

•Magnetic poles that are unlike attract each other, alike poles repel.

•Just like electric charges!

•Magnetic force is the attraction or repulsion between magnetic poles.

•Produced when magnetic poles interact

•Any material that exerts magnetic force is considered a magnet

Magnetic Fields•The magnetic field is the area of magnetic force around a magnet

•Allows magnets to interact without touching

•Magnetic field lines are the invisible lines that map out the magnetic field of a magnet

•Form complete loops, never cross

•Always leave north and enter south

•Distance between field lines indicate the strength of the magnet

•Closer the lines, stronger the lines

Magnetic Domains•A magnetic domain is a region where the magnetic fields of all atoms are lined up in one direction

•If the material is NOT magnetized, the magnetic domain points in random directions

•If the material is considered a magnet, the magnetic domains are arranged in the same direction

Magnetic Materials•A ferromagnetic material is a material that shows strong magnetic properties

•Behaves like a piece of iron

•Iron, nickel, cobalt, samarium

•Alloy magnets - magnets made from several different metals

•Alnico - aluminum, nickel, iron, cobalt

•Platinum and cobalt

•Ferrite - mixture of substances that contain ferromagnetic elements

•Most commonly used today

•Brittle material but inexpensive

Making Magnets•Unmagnetized material can be magnetized

•Placing an unmagnetized ferromagnetic material in a strong magnetic field

•By rubbing the material with one pole of a magnet

•Magnetizing a paper clip

•Rub the paperclip in one direction along one pole of the magnet

•Magnetic field of the magnet causes some domains in the paperclip to line up.

Destroying Magnets•Temporary magnet is a magnet made from a material that easily loses its magnetism

•Permanent magnet is a magnet made from a material that keeps its magnetism for a long time

•No magnet can last forever

•Ways to demagnetize magnets

•Drop it

•Strike it

•Heat it

Breaking Magnets•Break a magnet in half and you will have two smaller magnets

•Each smaller magnet has its own north pole and south pole

•Magnetic poles are lined up in one direction, which will remain even if the magnet is broken

S N

MAGNETIC EARTH

Earth as a Magnet

•In the 1500s, Sir William Gilbert decided to investigate compasses

•Gilbert confirmed that a compass always points in the same direction, no matter where you are

•Gilbert hypothesized that the Earth is simply a giant magnet

•Was Gilbert correct?

The Compass

•The north pole of the magnet will point towards the North Pole

•The poles of the magnetized needle on the compass align themselves with the Earth’s magnetic fields

•The Earth does not actually have a bar magnet buried within its core – just an analogy!

The Unknown Core

•Seismologists still do not completely understand Earth’s magnetism

•They theorize that the inner core of the Earth is made up of molten iron

•The circulation of molten material inside the Earth’s core is what causes Earth’s magnetism

Earth’s Poles•T

he Earth rotates on its axis around the geographic poles

•The magnetic poles are located on Earth’s surface where the magnetic force is the strongest

•Magnetic North Pole is actually located in Northern Canada – about 1,250 kilometers (about 776 miles) from the geographic North Pole

•Magnetic declination is the angle between the two lines – geographic north and magnetic north

Earth’s Magnetic Field

•Earth’s magnetic field acts on rocks• Rock is produced in the ocean floor from molten material that seeps up through the mid-ocean ridge• The iron in the rock lines up in the direction of the Earth’s magnetic field• Rock cools and hardens and the iron is locked in place• This process creates a permanent record of the magnetic field

•As scientists have been studying such rocks, they have discovered that the direction and strength of the Earth’s magnetic field have changed over time

•Earth’s magnetic field has completely reversed direction every million years or so

Mid-ocean ridge

Molten Material

Earth’s mantleOceanic crust

Rock formed when Earth’sMagnetic field was normal

Rock formed when Earth’sMagnetic field was reversed

The Magnetosphere

Van Allen belts – two regions that contain electrons and protons traveling at very high speeds

The Magnetosphere

•Solar wind is a stream of electrically charged particles flowing at high speeds from the sun

•Pushes against Earth’s magnetic field and surrounds the field

•The region shaped by the field is known as the magnetosphere.

Pictures of

The Earth’s Magnetosphere

Auroras

•When high-speed, charged particles get close to Earth’s surface, they interact with atoms in the atmosphere

•This results in the atoms giving off light

•A curtain of shimmering bright light in the atmosphere

•This glowing region caused by charged particles is called an aurora.

•Known as The Northern Lights, or aurora borealis in the North and the Southern Lights or aurora australis in the South.