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Unit Eight

OPTICS
READING PASSAGE
Spectral analysis
We mentioned compounds of calcium, lithium, and strontium without specifying which
compounds we were talking about. This may have given you the impression that only the
spectrum of one of the elements in a compound can be observed. It is true that the flame of
your alcohol burner is hot enough to produce the spectra of sodium, lithium, calcium, copper,
and a few other elements, but that is not hot enough to produce the other spectra of elements,
such as oxygen and chlorine. However, if we heat a sample of a compound to a sufficiently
high temperature (for example, by putting it in an electric arc), the spectra of all the elements
in the compound will be observed. Under such conditions, the resulting spectrum is no longer
simple. It will most likely contain complicated patterns of many closely spaced lines. Yet
each element gives out its own spectrum, which is different from that of any other. It takes
accurate measurements of the positions of spectral lines to identify an element. Once this has
been done, however, the presence of that element has been definitely established.
With a good instrument, it is observed that the yellow of the sodium flame is not just
any yellow. It is a very specific color indeed, which has its own special place in the
spectrum. It is a yellow made by no other element. The presence of this particular pair of
lines always means that sodium is present in the light source. Even if the yellow color is
hidden from the unaided eye by many colors, the spectroscope will show the presence of
sodium.
Although calcium, lithium, and strontium give flame tests of nearly the same color, each
gives its own set of characteristic spectral lines when viewed through a spectroscope. The
spectroscope thus enables us to distinguish one element from another.
Spectral analysis, or spectroscopy, can be done on tiny quantities of matter, such as
very small sample of a rare mineral or of a biological material. Spectroscopy can even be
used to determine the presence of different elements in distant objects like our sun and other

1. How are the spectra of all elements in a compound completely observed?
…………………………………………………………………………………………
………..……………………………………………………………………
2. Why is the yellow color of a sodium flame not just any yellow but a specific
one?
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………..……………………………………………………………………
3. What is the term used to refer to spectral analysis?
…………………………………………………………………………………………
………..……………………………………………………………………
4. What is the major function of spectroscopy?
…………………………………………………………………………………………
………..……………………………………………………………………
5. In the very present, in which way spectroscopy is more helpful?
…………………………………………………………………………………………
………..……………………………………………………………………

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Exercise 2: Decide whether each of the following statements is true (T) or false (F) or
without any information to identify (N).
1. …………. It is impossible to see the spectra of oxygen and chlorine by using alcohol
burner.
2. ………….The positions of spectral lines of an element help identify the element.
3. ………….Some elements may have some similar spectral lines.
4. ………….Calcium, lithium and strontium give the same spectra.
5. ………….Applying spectral analysis helps to detect new elements.
Exercise 3: Matching each of the words/phrases from column I with its definition from
column II
Column I Column II
1. to observe

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Paragraph two: Electron is a subatomic particle and one of the basic constituents of
matter. The electron was discovered by J.J. Thomson. It is found in all atoms and contains the
smallest known negative electrical charge.
Compare the two sentences, one from each paragraph
Thomson discovered the electron.
And The electron was discovered by Thomson.
The two sentences have the same meaning but different topics: they are about different
things, hence having different implications. In the former one, the topic is Thomson while in
the latter one the electron. We say the two sentences have different subjects. So what is the
significance of the difference between the two ways of saying? The answer really lies in
whether we want to lay emphasis on the doer of the action (we call it the agent) or the action
(sometimes the result of the action) itself.
In this pair of sentences, the first one is called an active sentence while the second is
called passive sentence. Look at the verb phrase of each sentence: "discovered" and "was
discovered"
Therefore, we deduce that the verb phrase in passive sentences is formed by combining
the auxiliary verb to be and a passive particle (exactly the same form as a part participle)
To be + P
II

In which the auxiliary verb to be bears all the grammatical changes in tenses and aspects
and others.
1. Present tenses:
1. Many elements are not so easily identified.
2. Once this has been done, however, the presence of that element has been definitely
established.
3. When the experiment is being conducted, there should be no changes in ambient
temperature.
2. Past tenses:

The underlined phrase is called by-phrase (forming by by + agent). This gives the new
information (by whom) to clarify the topic (subject) which is an already -known piece of
information (the electron was discovered). However, in science documents, the actions and
their result are much more important, the by-phrase becomes little important, hence forming
the impersonal passive to be frequently used.
In scientific documents, the following special patterns of passive are taken much use
of:
1. The passive with get:
Instead of be, sometimes we use get to form passive sentences:
Example:
1. If the spring is stretched beyond its elastic limit, it will get deformed.
2. Everything gets attracted to the center of the earth no matter where they are.
3. When you do the experiment, be careful or you may get burned.
However, get is mainly used in informal English, and it has more limited use than be.
The passive with get expresses action and change, not a state. It often refers to something
happening by accident, unexpectedly or incidentally.

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2. The passive with verbs of reporting
There are two special patterns with verbs of reporting which are frequently used in
science writing.
Active: Long time ago, people believed that the earth had a round shape.
Passive: Long time ago, it was believed that the earth had a round shape.
Long time ago, the Earth was believed to have a round shape.
Thus, we have:
Pattern one: It + passive verb + finite clause
More examples:
1. It is specified that gravitational potential is also a scalar.
2. It might be thought that the force needed to lift something is greater than its weight.
3. It has been proved that the force of gravity is an attractive force between any two

recommend
report*
say*
see*
show*
specify
state
suggest
suppose*
think*
understand*
Pattern two: Subject + passive verb + to-infinitive
More examples:
1. Gravitational potential is shown to increase by drawing equipotential lines onto a
diagram of the field lines.
2. It was about only 100 years ago that a way was discovered to separate aluminum
from oxygen by electrolysis.