Chapter 19 Section 2 & 3Magnetic Domains and the Earth

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Magnetic Domains• Matter is made of

atoms.• Nucleus = center=

protons (positive charge) & neutrons (neutral)

• Electrons = outside nucleus= negative charge

• Spinning electrons produce a magnetic field that acts like a tiny magnet.

• Most atoms have electron pairs that spin in opposite directions and cancel out the magnetic field.

• Therefore most matter have weak magnetic properties.

• When electrons are NOT paired the matter have strong magnetic properties.

• When magnetic fields of groups of atoms align themselves it is called a magnetic domain.

• Most domains are misaligned and point in random directions.

Domains

Magnetized Unmagnetized

Magnetic Materials

• Materials that have domains aligned are magnetic.• Materials that show strong magnetic

properties are called ferromagnetic.–Ex: • Common-nickel, cobalt, gadolinium• Rare- samarium and neodymium

• Alloys- magnets made form several metals– Ex:• Alnico= aluminum,

nickel, and cobalt• Cheap magnets are

made form ferrite

Making & Changing Magnets

• Magnets can be made, destroyed, or broken.Made• Material can be magnetized by putting it in a

strong magnetic field or by rubbing it with one pole of a magnet

• Temporary magnets- materials that magnetize easily but lose magnetism quickly

• Permanent magnets- materials that are hard to magnetize but stay magnetized for a long time

Destroyed• Drop or strike a magnet hard to knock the

domains out of alignment• Heating a magnet; temperature depends on

material• All ferromagnetic material can lose its

magnetic properties.

Break• If you break a

magnet, the domains are still aligned.

• Because the domains are still aligned, the magnet produces a strong magnetic force at the poles and a new South pole is generated.

Earth• Earth is a giant magnet– Has a magnetic field– Has 2 magnetic poles

• Earth’s core is liquid iron & nickel– Circulation of molten material produces a

magnetic field• Because Earth makes a strong magnetic field,

it can make magnets out of ferromagnetic materials– The domains line up with Earth’s magnetic field.

• A compass uses a magnetized needle that spins freely; points north

• When you use a compass you must considered the magnetic declination.– The angle between the

geographic pole and the magnetic pole• Angle will vary depending

on your location– The magnetic declination

has changed over time.

Earth’s Record• Earth’s magnetic field acts on magnetic material as

divergent boundaries produce new rock.– Iron in molten material lines up in the direction of

Earth’s magnetic field.– When the rock hardens, the iron is locked in place,

leaving a record.– Scientists have studied ocean rocks and

discovered that the direction and strength of Earth’s magnetic field has changed over time.

– Magnetic reversals (compass points south) have happened many many times.

– Why? We don’t know• Could be changes in the core

Magnetosphere

• Earth’s magnetic field that extends into outer space that is shaped by solar winds.

• Affects movements of electrically charged particles

Van Allen Belts- 2 inner magnetic fields that are shaped like donuts

• Most solar wind does not penetrate the magnetic field.

• When they do, they interact with the atmosphere and produce auroras (Northern Lights).