Warmup:

1
Warm-up

• Briefly describe the three different ways to
  charge an object.
• What is a magnet?

2
Electrostatics WS

• Any questions?

3
Magnetism

• What is a magnet?
• Until 1820, magnetism and electricity were
  thought to be completely separate phenomena.
• Hans Christian Oersted, while teaching a science
  class, noticed that a current-carrying wire could
  cause a compass to change its direction. (Demo)
• So, magnetism moving electric charges!!!

4
Magnetism

• How is magnetism similar to electric charge?
• Opposites attract, likes repel
• They both exert a force at a distance
• The force from both decrease by the 1/r2
  relationship as distance increases

5
Magnetism

• How is magnetism different than electric charge?
• Charge can move, while magnetism is a permanent
  property of an object.
• Charges can exist as and by themselves
  (protons and electrons), while magnetic poles
  (North and South) can only exist in pairs.
• In other words, you cannot have just a North
  magnet or just a South magnet

6
Magnetism

• So what causes magnetism in some metals?
• Some metals, such as iron, nickel, and cobalt,
  are magnetic.
• ALL magnetism is caused by moving electric
  charges
• so where is the moving electric charge inside
  these metals?

7
Magnetism

• The magnetism comes from the spinning of
  electrons

8
Magnetism

• Most elements have pairs of oppositely spinning
  electrons that cancel each other out
• Result NO magnetism

9
Magnetism

• Magnetic atoms have unpaired electrons
• For example, each iron atom has 4 unpaired
  electrons, so it makes a very good magnet.
• Result STRONG magnetism!!

10
Magnetic Fields

• Force Fields are they science fact or just
  science fiction?
• Actually, force fields do existwe live in the
  force field of gravity all the time.
• Also, surrounding every magnet is a magnetic
  force field (we usually just call it a magnetic
  field)
• (Iron filings demo)

11
Magnetic Fields

• Mini-Lab Magnetic field tracing
• Place your magnet in the center of your paper and
  trace it (label N and S ends)
• Beginning at one end, place the small compass on
  the paper and make a dot on your paper where the
  arrow points.
• Move the compass to the other side of the dot and
  repeat. Trace about 6 lines.

12
Magnetic Fields

• Magnetic force on moving charged particles
• When a charged particles moves through a magnetic
  field, a force is exerted on it.

N S
13
Magnetic Fields

• Magnetic force on moving charged particles
• This force is greatest when the charged particle
  moves perpendicular to the magnetic field lines.
• The force is zero when the charged particle moves
  parallel to the field lines.
• We can predict the direction of this force using
  the LEFT-HAND RULE (for negative charges)
• (This is how CRTs work for TVs and monitors)

14

• Check for Understanding which charged particles
  will feel the most force? Which will feel no
  force?

C
N S
A
D
B
15
Magnetic Fields

• There is a magnetic field that surrounds our
  planet

South Magnetic Pole North Magnetic Pole
16
Magnetic Fields

• There is a magnetic field that surrounds our
  planet

The earths magnetic pole is actually about 1100
miles away from the geographic North Pole. This
difference is called magnetic declination. Your
compass points to the magnetic pole, not the
geographic pole.
17
Magnetic Fields

• There is a magnetic field that surrounds our
  planet

Our planets magnetic field protects us from
cosmic radiation.
(There is less protection at the North and South
poles). Why?
18
Magnetic Fields

• There is a magnetic field that surrounds our
  planet

We are still not sure what causes the Earths
magnetic field.
The field is not stable, and has actually flipped
over 20 times in the last 5 million years!!!
19
Homework

• Read pages 562 568
• Begin working on the Electricity Magnetism
  Worksheet
• finish it as homework