MagnetismMagnetismMagnets and Magnetic Magnets and Magnetic

FieldsFields

PhysicsPhysics

Chapter 21 Section Chapter 21 Section 11

Pages 766-769 Pages 766-769

I. MagnetsI. Magnets

A. Magnets have two poles (ends)A. Magnets have two poles (ends)

1. North pole1. North pole

2. South pole2. South pole

A magnet will attempt to line itself up A magnet will attempt to line itself up with the magnetic field of the Earthwith the magnetic field of the Earth

I. MagnetsI. MagnetsB. Technological applications of magnetismB. Technological applications of magnetism

1. Large electromagnets used to pick up heavy 1. Large electromagnets used to pick up heavy loadsloads

2. Magnets used in meters, motors, 2. Magnets used in meters, motors, loudspeakersloudspeakers

3. Magnetic tapes used in audio and video 3. Magnetic tapes used in audio and video recording, and computer disksrecording, and computer disks

4. Regulation of controlled nuclear fusion 4. Regulation of controlled nuclear fusion researchresearch

5. Maglev trains5. Maglev trains

I. MagnetsI. MagnetsC. Magnetic forces exist between magnetsC. Magnetic forces exist between magnets1. Like poles repel (south-south, or north-1. Like poles repel (south-south, or north-

north)north)2. Opposite poles attract (south-north)2. Opposite poles attract (south-north)

I. MagnetsI. Magnets

D. Magnetic poles always occur in pairsD. Magnetic poles always occur in pairs

1. Magnetic poles can never be 1. Magnetic poles can never be isolatedisolated

2. If you break a magnet, each piece 2. If you break a magnet, each piece will have a north and a south polewill have a north and a south pole

I. MagnetsI. MagnetsE. Permanent magnetsE. Permanent magnets

1. Unmagnetized iron can be 1. Unmagnetized iron can be magnetized by placing it near a strong magnetized by placing it near a strong permanent magnet or stroking it with permanent magnet or stroking it with a magneta magnet

2. Process is reversible with heat 2. Process is reversible with heat

or hammeringor hammering

I. MagnetsI. Magnets

I. MagnetsI. Magnets

I. MagnetsI. Magnets

3. Magnetic material is classified by how it 3. Magnetic material is classified by how it retains its magnetismretains its magnetism

a. Soft – easy magnetized, but easily a. Soft – easy magnetized, but easily loselose

the magnetismthe magnetism

b. Hard – not easily magnetized, but b. Hard – not easily magnetized, but onceonce

magnetized retain magnetismmagnetized retain magnetism

II. Magnetic fieldsII. Magnetic fields

II. Magnetic fieldsII. Magnetic fields

A region in which a magnetic force A region in which a magnetic force can be detectedcan be detected

A. Direction of a magnetic field is the A. Direction of a magnetic field is the direction in which the north pole of a direction in which the north pole of a compass needle points at that location compass needle points at that location (Figure 21-2, page 767)(Figure 21-2, page 767)

Magnitude of the field is higher closer Magnitude of the field is higher closer to the poleto the pole

II. Magnetic fieldsII. Magnetic fields

II. Magnetic fieldsII. Magnetic fields

B. To indicate B. To indicate

1. In the plane of the page: 1. In the plane of the page: 2. Into the page: X2. Into the page: X

3. Out of the page: •3. Out of the page: •

II. Magnetic fieldsII. Magnetic fields

C. North-seeking vs. South seekingC. North-seeking vs. South seeking

1. Bar magnets will seek or point to the 1. Bar magnets will seek or point to the Geographic north or south pole.Geographic north or south pole.

2. Geographic north = magnetic south2. Geographic north = magnetic south

3. Geographic south = magnetic north3. Geographic south = magnetic north

II. Magnetic fieldsII. Magnetic fields

II. Magnetic fieldsII. Magnetic fields

D. True North vs. Magnetic NorthD. True North vs. Magnetic North

Magnetic declination – difference Magnetic declination – difference between compass pointing at between compass pointing at magnetic north and true / geographic magnetic north and true / geographic northnorth

II. Magnetic fieldsII. Magnetic fields

E. Earth’s field is like a bar magnet E. Earth’s field is like a bar magnet buried in the Earth buried in the Earth

Convection current in Earth’s liquid Convection current in Earth’s liquid iron outer core are the source of the iron outer core are the source of the fieldfield

Related to planet rotation.Related to planet rotation.