Magnetism and Electromagnetism

1
Magnetism and Electromagnetism

• Chapter 19

2
The Nature of Magnetism

• magnetism - the force of attraction or repulsion
  of magnetic materials
• magnetic pole - the ends of a magnetic object,
  where the magnetic force is strongest.
• North and south poles
• Magnetic poles that are alike repel each other
  and magnetic poles that are unlike attract each
  other
• What happens when you break a magnet?

3
Magnetic Field

• The region around a magnet where the magnetic
  force is exerted
• magnetic field lines - Diagram pg.615
• magnetic field interactions - Diagram pg.616

4

• In a magnetized material, all or most of the
  domains are arranged in the same direction pg.617
• making magnets - metallic object in a strong
  magnetic field, or rub it with a strong magnet
• destroying magnets - drop it or strike it, heat
  it up

5
Magnetic Earth

• compass - a device with a magnetized needle that
  can spin freely
• Earth has an immense magnetic field surrounding
  it, just as there is a magnetic field around a
  bar magnet
• magnetic declination - the angle between
  geographic north and the north to which a compass
  needle points pg. 624

6
Magnetic Earth (cont.)

• Earths magnetic field affects the movements of
  electrically charged particles in space. Charged
  particles also affect the Earths magnetic field.
• Molten rocks that harden can also indicate the
  direction of the earths magnetic field at the
  time the rocks cooled

7
Electric Current and Magnetic Fields

• electric charge - a property of electrons and
  protons
• electrons carry a negative charge
• protons carry a positive charge
• electric current - the flow of a charge through a
  material
• an electric current produces a magnetic field

8
Electric circuit

• A complete path though which electric charges can
  flow
• Circuit must have
• 1) source of electrical energy,
• 2) devices run by electrical energy,
• 3) conducting wires and a switch

9

• conductor - electric currents move freely
• insulator - electric current does not flow
  easily, electrons bound tightly to their atoms
• resistance - the opposition to the movement of
  electrical charges flowing through a material
• superconductors - material that has no electrical
  resistance

10
Electromagnets

• solenoid - a current carrying coil of wire with
  many loops that acts as a magnet
• electromagnet - a solenoid with a ferromagnetic
  core that forms a magnet that can be turned on
  and off
• increasing strength of electromagnet - increase
  current, increase number of loops of wire
• recorders - vibrations of voice are changed into
  electric current, recorded as change in magnetic
  field. Create magnetic pattern.