CSET Practice Test Subtest II Science

Neon Lights

The idea behind a neon light is simple. Inside the glass 
tube there is a gas like neon, argon or krypton at low 
pressure. At both ends of the tube there are metal 
electrodes. When you apply a high voltage to the 
electrodes, the neon gas ionizes, and electrons flow 
through the gas. These electrons excite the neon 
atoms and cause them to emit light that we can see. 
Neon emits red light when energized in this way. Other 
gases emit other colors.

THE MOTION OF CELESTIAL BODIES

Ptolemaic or geocentric theory

The first theory explaining the structure of the Universe 
and the motion of celestial bodies was proposed by 
Aristotle, in the IV century B.C. According to this 
theory, all celestial bodies (the Moon, Mercury, Venus, 
the Sun, Mars, Jupiter, Saturn and the so-called "fixed 
stars") were inserted in concentric rigid spheres, which 
uniformly rotate around the Earth. The several peculiarities 
of the planetary motions, were explained by means of 
complicated motions along circumferences centered on 
theses spheres. 

Celestial spheres were perfect and unchanging. 

The geocentric theory was commonly accepted until the 
XVI century, when the Polish astronomer Nicolaus 
Copernicus (1473-1543) conceived the hypothesis that 
the Sun, not the Earth, is the center of the Universe. 

Copernican or heliocentric theory

Copernicus said that the Earth is a simple planet orbiting 
the Sun, just like the other ones. This theory is then 
called heliocentric. Copernicus' hypothesis was supported 
by an accurate study which explained the motion of 
planets. However, the scientific community strongly 
opposed to the theory. Its definitive affirmation was 
due to the studies by Galileo Galilei (1564-1624), and to 
the demonstration that the orbits of all planets are ellipses, 
where the Sun occupies on the the two foci. Johannes 
Kepler (1571-1630) provided this demonstration, using 
the observations carried out by the Danish astronomer 
Thyco Brahe. We know today that the Sun is not the 
center of the Universe. It is just one of the many stars 
in our Galaxy, and the latter in just one of the galaxies 
populating the Universe.  A sketch illustrating the 
heliocentric theory, from Copernicus' "De rivolutionis". 

Kepler enunciated three laws that rule the motion of 
the planets around the Sun. This motion is called 
"revolution". The time a planet takes to go back to the 
same point of its orbit, is called "period" of the revolution. 
Kepler's three laws were deduced from the observations 
without any theoretical basis. Isaac Newton (1642-1727) 
later revealed that these laws are just special cases of 
the universal gravitational law, which describes the 
interactions between any physical bodies. 

KEPLER'S FIRST LAW 

All planets move around the Sun on elliptical orbits. The 
Sun occupies one of the two foci, the same focus for all 
ellipses. 

The ellipse is a plane figure, obtained by cutting a cone 
with a plane not orthogonal to its axis. The sum of the 
distances from two points, called foci, to any of of its 
points is constant. Since planets describe elliptical orbits, 
the Sun-planet distance varies as a function of time, and 
it has a maximum and a minimum values. The former occurs 
when the planet is in a point called "aphelion", while the 
latter occurs when it is in the "perihelion". The ratio of the 
distance from one focus to the center, over the length of 
the semimajor axis, is called "eccentricity" of the ellipse. A 
circumference can be imagined as a special ellipse, whose 
eccentricity is zero. 

KEPLER'S SECOND LAW 

The vector radius covers equal areas in equal times. 

The vector radius connects the center of the Sun to that 
of the planet. Its length changes along the orbit. If we 
take two equal areas defined by the vector radius, the 
second law implies that the planet's revolution is not 
constant in speed. It is faster at the perihelion, and slower 
at the aphelion. 

KEPLER'S THIRD LAW 

The revolution periods of planets, squared, is proportional 
to the major semiaxis of their orbits, raised to the third 
power. 

This law implies that the larger is the distance from the 
Sun, the slower is a planet's revolution. In fact, the 
closer to the Sun it is, the more the planet is affected 
by its attraction. Therefore, it must move faster in order 
not to fall upon it. Actually, both the Sun and the planet 
rotate around the common baricenter, but the Sun is 
much more massive than the planet. The baricenter then 
almost coincides with the Sun's center, so the only 
apparent revolution is that of the planet. This behavior 
is true each time a body rotates around a more massive 
one. Indeed, these laws are not only valid for the planets 
in the Solar System, but also for any celestial body. 

If two bodies have comparable masses, then their 
baricenter does not coincide with any of them, and their 
orbit around this point become visible. This is the case, 
for example, of binary stars. 

If instead there are three or more bodies with comparable 
masses, then their relative orbits cannot be predicted by 
any laws of Mechanics, since their description becomes 
too complex. 

UNIVERSAL GRAVITATIONAL LAW 

Kepler's three laws are just the consequence of Newton's 
universal gravitation law. It was enunciated in 1688: 

Each body exerts an attractive force on any other body. 
The force is directed along the direction joining the two 
bodies. Its intensity is directly proportional to the product 
of their masses, and inversely proportional to the square 
of their distances. 

If we have two bodies, whose masses are M1 and M2, 
and whose distance is r, the attractive force is equal to 
F = K (M1 M2)/r2 

where K is called universal gravitation constant. It does 
not depend on the shape, the size or the chemical 
composition of the bodies. This law tells that each planet 
attracts the other ones just like the Sun, but with a much 
smaller strength. The result is that the planets' orbits are 
actually not perfect ellipses, since they are affected by 
gravitational perturbations caused by the rest of the 
planets. 

ROTATION 

Revolution is not the only motion of planets around the 
Sun. The other main motion is that of rotation around one 
axis. The time interval taken ot complete one turn is called 
"rotation period", or "day". A result of the rotation is the 
alternation of "day" and "night", just like a result of the 
revolution is the alternation of the seasons. 

Motion in the Heavens: Stars, Sun, Moon, Planets
excerpts from a lecture by Michael Fowler, Physics 
Department University of Virginia

The purpose of this lecture is just to review the various 
motions observed in the heavens in the simplest, most 
straightforward way. We shall ignore for the moment 
refinements like tiny deviations from simple motion, but 
return to them later. 

It is illuminating to see how these observed motions 
were understood in early times, and how we see them 
now. Of course, you know the earth rotates and orbits 
around the sun. However, I want you to be bilingual for 
this session: to be able to visualize also the ancient view 
of a fixed earth, and rotating heavens, and be able to 
think from both points of view. 

This is really largely an exercise in three-dimensional 
visualization -- that's the hard part! But without some 
effort to see the big picture, you will not be able to 
appreciate some really nice things, like the phases of the 
moon, eclipses, and even just the seasons. You really 
need to have a clear picture of the earth orbiting around 
the sun and at the same time rotating about an axis tilted 
relative to the plane the orbit lies in, with the axis of 
rotation always pointing at the same star, and not 
changing its direction as the earth goes around the sun. 
Then you must add to your picture the moon orbiting 
around the earth once a month, the plane of its orbit 
tilted five degrees from the plane of the earth's orbit 
around the sun. Then we add in the planets … . 

Some of these topics are treated nicely in Theories of 
the World from Antiquity to the Copernican Revolution, 
by Michael J. Crowe, Dover $6.95. 

Looking at the stars 
There is one star that always stays in the same place 
in the sky, as seen from Charlottesville (or anywhere 
else in the northern hemisphere). This is Polaris, the 
North Star. All the other stars move in circular paths 
around Polaris, with a period of 24 hours. This was 
understood in ancient times by taking the stars to be 
fixed to the inside surface of a large sphere, the "starry 
vault", which was the outer boundary of the Universe, 
and contained everything else. 

Of course, we only see the stars move around part of 
their circular path, because when the sun comes up, the 
bright blue scattered sunlight - the blue sky - drowns 
out the starlight. If there were no atmosphere, we would 
see the stars all the time, and see the complete circles for 
those that stayed above the horizon. 

Try to picture yourself inside this large, spherical rotating 
starry vault with stars attached, and visualize the paths 
of the stars as they wheel overhead. Think about the 
paths the stars would take as seen from the North Pole, 
from the Equator, and from Charlottesville. 

Motion of the sun 
Every day the sun rises in the east, moves through the 
southern part of the sky and sets in the west. If there 
were no atmosphere so that we could see Polaris all the 
time, would the sun also be going in a circular path 
centered on Polaris? 

The answer is yes - (well, almost). 

If you were at the North Pole in the middle of summer, 
lying on your back, you would see the sun go around in 
a circle in the sky, anticlockwise. The circle would be 
centered on Polaris, which is directly overhead, except 
for the fact that you wouldn't see Polaris all summer, 
since it wouldn't be dark. Here of course we see the sun 
circling part of the time, and see Polaris the other part of 
the time, so it isn't completely obvious that the sun's 
circling Polaris. Does the sun circle clockwise or anticlockwise 
for us? It depends on how you look at it - in winter, when 
it's low in the sky, we tend to look "from above", see the 
sun rise in the east, move in a low path via the south 
towards the west, and that looks clockwise - unless you're 
lying on your back. 

Actually the sun moves very slightly each day relative to 
the starry vault. This would be obvious if there were no 
atmosphere, so we could just watch it, but this can also 
be figured out, as the Greeks and before them the 
Babylonians did, by looking closely at the stars in the west 
just after sunset and seeing where the sun fits into the 
pattern. 

It turns out that the sun moves almost exactly one degree 
per day against the starry vault, so that after one year it's 
back where it started. This is no coincidence - no doubt 
this is why the Babylonians chose their angular unit as the 
degree (they also liked 60). 

Anyway, the sun goes around in the circular path along 
with the starry vault, and at the same time slowly 
progresses along a path in the starry vault. This path is 
called the ecliptic. 

If we visualize Polaris as the "North Pole" of the starry 
vault, and then imagine the vault's "Equator", the ecliptic 
is a great circle tilted at 23 ½ degrees to the "equator". 
The sun moves along the ecliptic from west to east. 
(Imagine the earth were not rotating at all relative to the 
stars. How would the sun appear to move through the 
year?) 

The motion of the sun across the starry vault has been 
known at least since the Babylonians, and interpreted in 
many colorful ways. Compare our present view of the stars, 
thermonuclear reactions in the sky, with the ancient view 
(see Hemisphaerium Boreale, Appendix to Heath's Greek 
Astronomy). 

Many of the ancients believed, to varying degrees, that 
there were spirits in the heavens, and the arrangements of 
stars suggested animals, and some people. 

The sun's path through all this, the ecliptic, endlessly 
repeated year after year, and the set of constellations (the 
word just means "group of stars") and the animals they 
represented became known as the Zodiac. ( "zo" being the 
same Greek word for animal that appears in "Zoo".) So this 
is your sign: where in its path through this zoo was the sun 
on the day you were born? 

Notice that the print shows the sun's path through the 
northern hemisphere, that is, for our summer. The furthest 
north (closest to Polaris) it gets is on June 21, when it is in 
Cancer, it is then overhead on the Tropic of Cancer, 23½ 
degrees north of the Equator. 

In other words, the spherical earth's surface is visualized 
as having the same center as the larger sphere of the starry 
vault, so when in its journey across this vault the sun reaches 
the tropic of the vault, it will naturally be overhead at the 
corresponding point on the earth's tropic which lies directly 
below the tropic on the vault. 

Motion of the moon against the starry vault 
The sun goes around the starry vault once a year, the moon 
goes completely around every month. 

Does it follow the same path as the sun? 

The answer is no, but it's close - it always stays within 5 
degrees of the ecliptic, so it goes through the same set of 
constellations - "the Moon is in the Seventh House" and all 
that. In fact, the "houses" - the signs of the Zodiac - are 
defined to occupy a band of the stars that stretches eight 
degrees either way from the ecliptic, because that turns 
out to be wide enough that the sun, moon and all the 
planets lie within it. 

How can we understand the Moon's motion from our 
present perspective? If the earth, the moon and the sun 
were all in the same plane, in other words, if the moon's 
orbit was in the same plane as the earth's orbit around the 
sun, the Moon would follow the ecliptic. In fact, the Moon's 
orbit is tilted at 5 degrees to the earth's orbit around the 
sun. 

This also explains why eclipses of the moon (and sun) don't 
happen every month, which they would if everything was in 
the same plane. In fact, they only occur when the moon's 
path crosses the ecliptic, hence the name. 

Motion of the planets 
Since ancient times it has been known that five of the 
"stars" moved across the sky: Mercury, Venus, Mars, Jupiter 
and Saturn. They were termed "planets" which simply means 
wanderers. 

Are their paths in the starry vault also related to the 
ecliptic? 

The answer is yes - they all stay within 8 degrees of the 
ecliptic, and in fact this is the definition of the Zodiac - 
the band of sky within eight degrees of the ecliptic, and 
for this reason. 

Do they go all the way round? 

Yes they do, but Mercury never gets more than 28 degrees 
away from the sun, and Venus never more than 46 degrees. 
Thus as the sun travels around the ecliptic, these two 
swing backwards and forwards across the sun. 

The other planets are not tethered to the sun in the same 
way, but they also have some notable behavior - in 
particular, they occasionally loop backwards for a few weeks 
before resuming their steady motion.

pH

Whether a compound is an acid or a base is indicated by 
its pH or "power of hydrogen," which represents the 
amounts of acid or base in a solution. Pure water is neutral, 
and so registers 7 on the pH scale. The lower the reading 
below 7, the more acidic a solution is. The higher the 
reading above 7, the more basic a solution is. The pH of 
lemon juice is about 2.3 -- acidic; the pH of seawater is 
about 8.3 -- basic. 

Most cleansers are bases; some are highly basic. 
Personal hygiene products are neither highly acidic nor 
highly basic. 
Few highly basic materials are edible; some fairly highly 
acidic materials are edible. 
Most facial products fall within pH 3-8. 
pH of saliva varies; most are acidic. 
Humans tolerate acids well, internally. 
Some products with the same pH have widely different 
uses.