Lesson Notes
Physical Sciences Grade 10
Magnetism
LESSON
4
Teacher Guide
Earth’s Magnetic Field
A compass needle moves in an external magnetic field. In 1600, the scientist William Gilbert explained how the needle
moved by introducing the concept of the earth’s magnetic field. The earth’s magnetic field protects the earth against
high-energy particles that stream in from space on the solar wind.
By the end of this lesson, learners should be able to:
• Describe the earth’s magnetic field
• Evaluate the impact of the earth’s magnetic field on
life on earth
Lesson Notes
It took a long time for navigators to understand why a
loadstone or compass needle turned to point in a specific
direction. Not until William Gilbert published his findings
in 1600 on his extensive research into the loadstone,
did people realise that the earth had its own magnetic
field. The reason that a compass needle always swings
to point in the same direction, is because it is being
influenced by the strong magnetic field that surrounds the
earth. The earth has a magnetic field just as a bar magnet
has a magnetic field.
The earth’s magentic field
What we have learnt so far is that a magnetic field is
3-dimentional. It is strongest at the poles. A compass
needle is itself a free-moving magnet that is affected
by the magnetic field of a permanent magnet. The field
direction outside a bar magnet is from north to south. The
magnetic field direction inside a bar magnet is from south
to north. The direction is indicated by an arrow. The field
lines never cross. The closer they are, the stronger the
field.
We need to understand the terminology used when
referring to the earth. The earth is divided geographically
into the North Pole and the South Pole. These are the
points around which the earth rotates. The earth’s axis
passes through these poles. The geographical poles are
fixed. They are not related to the magnetic field.
Curriculum Links
LO 3: T
he Nature of Science and its Relationship
to Technology, Society and the Environment
AS 2: E
valuate the impact of science on human
development
AS 3: E
valuate the impact of science on the
environment
A free-moving compass needle will point to what we
call magnetic north. This is different to the geographical
North Pole. We have seen that the north of one magnet
will repel the north of another magnet. The north of one
magnet will attract the south of another magnet. When
the north side of the compass needle is swinging towards
magnetic north of the earth, it is actually being attracted
by the earth’s magnetic south pole. Although we speak
about ‘magnetic north’, the pole is actual a magnetic
south.
There is a definite difference between the geographical
North Pole and the magnetic north pole of the earth. The
magnetic field of the earth moves all the time.
The magnetic field of the earth is not symmetrical like
the magnetic field around a bar magnet. The solar wind,
carrying high-energy particles from the sun, distorts the
shape of the magnetic field.
However, the earth’s magnetic field protects us from this
radiation and deflects the flow of charged particles into
space. Some charged particles are trapped in the earth’s
magnetic field and are drawn towards the poles. Here
these particles release energy in the form of light. This
extraordinary phenomenon, observed in Antarctica and
near the Arctic Circle, is called the aurora.
Lesson Outcomes
2
E
?
TASK
Write a report to show how magnetism has
impacted on life on earth. You can choose to write
about the impact on technology or the environment.
2+2=4
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