Magnetic Fields

96

Magnetic Fields

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97

Magnetic Poles

Every magnet has 2 poles ­ North and South
It's similar to the charge being either positive or negative

98

Forces between Magnetic Poles

Opposite magnetic poles attract.

Like magnetic poles repel.

Click here to launch a video
on magnetic levitation

99

The Compass

A compass is just a bar magnet that is free to swing about.
The compass needle is attracted to Earth's magnetic poles.

The compass is an indicator of
Earth's magnetic field.

100

Earth's Geographic
North Pole is actually a
Magnetic South Pole!

A compass' true North Pole is attracted to Earth's Geographic North Pole
(Magnetic South Pole), and vice versa.

Geographic and Magnetic Poles

Earth's Geographic
South Pole is actually a
Magnetic North Pole!

101

Magnetic Field Line Drawings

Forces around magnets can be visualized by "lines of force"
These lines indicate the strength of a magnetic field.

Where have we seen force lines like this before?

*sketch this

in the space provided

*note that arrows enter

South and exit North

102

3 Magnetic Field Line Rules

Lines exit North Poles and enter South Poles

Closer lines equal stronger force

Field lines never cross!

103

As we move away from a
magnetic pole, What
happens to the strength of
the magnetic field?

A

B

Compare the spacing of the field lines
at A vs. B

What do you notice?

Magnetic Field
Drawings

it gets more spread out which

means the magnetic force is
weaker

104

Visualizing Magnetic Fields

By sprinkling iron filings around a magnet, we see that they will line up
differently depending on the magnetic field of the magnet.

lines connect in middle so this is attraction

lines repel upward/downward

Multiple Choice

33 This photo depicts magnets which could be aligned _______________.

• North-North

• North-South

105

33 This photo depicts magnets which could be aligned _______________.

A North North

B North South

Answer

*not in notes but good extra practice*

repelling so must be same poles

Multiple Choice

33 This photo depicts magnets which could be aligned _______________.

• North-North

• North-South

106

34 This photo depicts magnets which could be aligned _______________.

A North North

B North South

Answer

*not in notes but good extra practice*

attracting so must be opposite poles

107

Magnetic Fields Lines

Can you visualize
the photos you
just saw with
these drawings?

108

Attractive force between unlike poles

This magnetic field line diagram shows an attractive force between
unlike poles.

109

Repulsive force between like poles

This magnetic field line diagram shows a repulsive force between
like poles.

south/south will

look exactly the
same but arrows
ENTER south

Multiple Choice

35 Like magnetic poles:

• attract

• repel

Multiple Choice

36 This type of field drawing represents:

• attraction

• repulsion

• suspension

112

36 This type of field drawing represents:

A

attraction

B

repulsion

C

suspension

Answer

Multiple Choice

39 Magnetic Field lines exit from the south pole of a magnet.

• True

• False

115

39 Magnetic Field lines exit from the south pole of a
magnet.

True

False

Answer

Multiple Choice

40 As distance is increased away from a magnetic field source, the magnetic field intensity will ___________.

• Increase

• Decrease

• Stay the same

116

40 As distance is increased away from a
magnetic field source, the magnetic
field intensity will ___________.

A

Increase

B

Decrease

C

Stay the same

Answer

inversely/indirectly proportional