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Unit Twelve
MAGNETISM
READING PASSAGE
Earth’s magnetic field
Scientists still do not know exactly what causes the earth’s magnetic field. In the 16th
century, it was believed that a mountain of magnetite (a magnetic mineral) was located at
the North Pole and that this mountain caused the earth’s magnetic field. English physician
William Gilbert was the first to propose, in 1600, that the earth itself was a massive
magnet. Current theories hold that the earth’s magnetic field is created by currents within
the liquid outer core of the earth, which is composed mostly of iron. This liquid core
contains ions, or electrically charged atoms and molecules. The motion of these charged
particles within the earth is thought to create the earth’s magnetic field.
Scientists sometimes find it easier to model the earth’s magnetic field as if it were a
perfectly symmetrical magnetic field coming from one large bar magnet. The poles of this
hypothetical magnetic field, based on averaging the direction and strength of earth’s magnetic
field, are called the geomagnetic poles. The north geomagnetic pole is located near Thule,
Greenland, 1250 km (780 miles) from the geographical North Pole. The south geomagnetic
pole is located near Vostok, Antarctica, 1250 km (780 miles) from the geographic South Pole.
Paleomagnetism is the study of the earth’s magnetic field in ancient times. Scientists can
study the earth’s ancient magnetic fields by measuring the magnetic orientation of certain
rocks. When molten rock crystallizes, crystals of magnetic minerals align with the earth’s
magnetic field. The rock thus records the direction of the earth’s magnetic field at the time of
its crystallization. By measuring the magnetic orientation and determining the age of such
rocks, scientists can measure the orientation of the earth’s magnetic field at different times in
the earth’s history. Geologists can use systematic paleomagnetic measurements on rocks of
different ages to map out the apparent movement of the earth’s magnetic field as a function of
time. This map defines what is known as a pole path. Differences in the pole paths of the
continents indicate the relative drift of these continents.
Paleomagnetic measurements played a key role in the development of the theory of plate

………………………………………………………………………………
4.

How can scientists measure the orientation of the earth’s magnetic field in the earth’s
history?
…………………………………………………………………………………………
………………………………………………………………………………
5.

Why did the paleomagnetic measurements use to be important?
…………………………………………………………………………………………
………………………………………………………………………………
Exercise 2:
Choose the best alternative
1.

Scientists now
a.

have had enough evidence about the cause of the earth’s magnetic field
b.

is still working hard in finding the cause of the earth’s magnetic field.
c.

have not understood all about the cause of the earth’s magnetic field
2.

William Gilbert
a.

b.

some kinds of rocks of the time
c.

a special kind of rock of that time
5.

Geologists use the result of paleomanetic measurements in order to
a.

find out the pole paths of the earth’s magnetic field.
b.

to study about the world’s continents.
c.

to map out the magnetic field of the earth’s as a function of time
Exercise 3:
Match each word in column A with its definition in column B

A B
1.

mid-ocean ridge
2.

strips
3.


d.

having two halves which are exactly the same, except
that one haft is the mirror image of the other.
e.

long narrow pieces of something
f.

the area in the middle of the ocean
g.

the direction an object faces or the direction of the line
along which the body exists
h.

the process in which a liquid or semi-liquid turns into a
solid
i.

the process of giving a substance the power to draw
iron and other metals towards it.
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GRAMMAR IN USE

The gerund
1. Gerund forms

3. Gerund clause
A gerund on its own or can be combined with other elements (with subject; object; or
adverbial) to form a clause:
Examples:
i.

conducting such an experiment
ii.

not being able to complete his thesis
iii.

having made enough observations
4. Functions of the gerund

110
A gerund can be treated as a noun/noun phrase, so it has a wide range of uses as a
noun/noun phrase
a.
A gerund can be treated as a noun on its own or can be used to modify another
noun
Example:
1.

Neighboring molecules beneath them are set into faster motion, and heat flows into
the floor.
2.

This is called the microwave background, and is the remnant of radiation from the
‘big bang’, the giant explosion that is believed to have occurred at the beginning

: What he has to do now is quickly finishing his research.
d.
As a prepositional complement
d.1.

As a complement after a preposition following a noun

Example
:
1.

The question of finding the cause of the earth’s magnetic field has drawn a great
attention from physicists.
2.

We can not see electric current in a wire, so we find different ways of explaining
what is going on.
The following nouns with their prepositions can be followed by a gerund 111
advantage of
aim of/in
amazement at
anger about/at
annoyance
about/at
anxiety about
apology for
awareness of

task of
work of

d.2. As a complement after a preposition following an adjective
Example:
1.

This internal energy spreads out, making it much less effective at producing work
than, say, the organized kinetic energy of a moving object.
2.

Energy has been called the “common denominator” of the natural science because its
conservation law makes it so useful in understanding any physical process.

The following are the adjectives with their prepositions that can take a gerund
afraid of
amazed at
angry about/ at
annoyed about/at
anxious abut
ashamed of
aware of
bad at
bored with
capable of
content with
dependent on
different from/to
excited about
famous for

by means of
despite
for
in
in addition to
in favor of
in spite of
instead of
on account of
since
through
what about
with

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before how about on without
Example:
1.

Absorption spectra of gases may be obtained by passing white light through a sample
of gas before the light enters the prism.
2.

By measuring the magnetic orientation and determining the age of such rocks,
scientists can measure the orientation of the earth’s magnetic field at different times
in the earth’s history.
3.

Using springs of various thickness, one can make scales for measuring very large and
also very small weights.

He’s thinking
of
taking a course of physics.
3.

Some energy goes into raising the temperature of the cylinder walls and the piston,
and that part spreads outward, doing no useful work
The following verbs take gerund as a direct object