CSET Practice Test Subtest II Science

The Food Chain

An ecosystem is a living community which depends on 
each member and its surrounding environment. The 
living part of an ecosystem is sometimes called a 
food chain.

Every participant in an ecosystem has an important 
part to play and if one becomes more dominant than 
the others, the ecosystem can develop problems. 

We'll start with the producers. These are living things 
which take the non living matter from the environment, 
such as minerals and gases and uses them to support 
life. Green plants are considered producers and the are 
at the beginning of the food chain. 

Next are the consumers. These living things need the 
producers to be their food.

Animals who eat plants are called herbivores. They are 
considered consumers and are next in the food chain. 

Animals who eat other animals are called carnivores. 
They also considered consumers and are a link farther 
along on the food chain since they need the herbivores 
for their food. 

Animals and people who eat both animals and plants are 
called omnivores, and they are also part of the consumer 
piece of the ecosystem. 

Finally, the last part of the ecosystem is the decomposers. 
These are the living things which feed off dead plants 
and animals and reduce their remains to minerals and 
gases again. Examples are fungi, like mushrooms, and 
bacteria.

The Light Bulb
by Tom Harris
How Stuff Works.com

Before the invention of the light bulb, illuminating the 
world after the sun went down was a messy, arduous, 
hazardous task. It took a bunch of candles or torches 
to fully light up a good-sized room, and oil lamps, while 
fairly effective, tended to leave a residue of soot on 
anything in their general vicinity. 

When the science of electricity really got going in the 
mid 1800s, inventors everywhere were clamoring to 
devise a practical, affordable electrical home lighting 
device. Englishman Sir Joseph Swan and American 
Thomas Edison both got it right around the same time 
(in 1878 and 1879, respectively), and within 25 years, 
millions of people around the world had installed electrical 
lighting in their homes. The easy-to-use technology was 
such an improvement over the old ways that the world 
never looked back. 

The amazing thing about this historical turn of events is 
that the light bulb itself could hardly be simpler. The 
modern light bulb, which hasn't changed drastically since 
Edison's model, is made up of only a handful of parts.

Light Basics
Light is a form of energy that can be released by an atom. 
It is made up of many small particle-like packets that have 
energy and momentum but no mass. These particles, 
called light photons, are the most basic units of light.

Atoms release light photons when their electrons become 
excited. An atom's electrons have different levels of 
energy, depending on several factors, including their 
speed and distance from the nucleus. Electrons of 
different energy levels occupy different orbitals. Generally 
speaking, electrons with greater energy move in orbitals 
farther away from the nucleus. When an atom gains or 
loses energy, the change is expressed by the movement 
of electrons. When something passes energy on to an 
atom, an electron may be temporarily boosted to a higher 
orbital (farther away from the nucleus). The electron only 
holds this position for a tiny fraction of a second; almost 
immediately, it is drawn back toward the nucleus, to its 
original orbital. As it returns to its original orbital, the 
electron releases the extra energy in the form of a 
photon, in some cases a light photon. 
The wavelength of the emitted light (which determines 
its color) depends on how much energy is released, which 
depends on the particular position of the electron. 
Consequently, different sorts of atoms will release different 
sorts of light photons. In other words, the color of the 
light is determined by what kind of atom is excited. 

This is the basic mechanism at work in nearly all light 
sources. The main difference between these sources is 
the process of exciting the atoms.

The Bulb
Light bulbs have a very simple structure. At the base, 
they have two metal contacts, which connect to the 
ends of an electrical circuit. The metal contacts are 
attached to two stiff wires, which are attached to a 
thin metal filament. The filament sits in the middle of the 
bulb, held up by a glass mount. The wires and the 
filament are housed in a glass bulb, which is filled with 
an inert gas, such as argon. 

When the bulb is hooked up to a power supply, an 
electric current flows from one contact to the other, 
through the wires and the filament. Electric current in 
a solid conductor is the mass movement of free electrons 
(electrons that are not tightly bound to an atom) from a 
negatively charged area to a positively charged area. 

As the electrons zip along through the filament, they 
are constantly bumping into the atoms that make up 
the filament. The energy of each impact vibrates an 
atom -- in other words, the current heats the atoms 
up. A thinner conductor heats up more easily than a 
thicker conductor because it is more resistant to the 
movement of electrons. 

Bound electrons in the vibrating atoms may be boosted 
temporarily to a higher energy level. When they fall back 
to their normal levels, the electrons release the extra 
energy in the form of photons. Metal atoms release 
mostly infrared light photons, which are invisible to the 
human eye. But if they are heated to a high enough 
level -- around 4,000 degrees Fahrenheit (2,200 degrees 
C) in the case of a light bulb -- they will emit a good 
deal of visible light. 

The filament in a light bulb is made of a long, incredibly 
thin length of tungsten metal. In a typical 60-watt bulb, 
the tungsten filament is about 6.5 feet (2 meters) long 
but only one-hundredth of an inch thick. The tungsten 
is arranged in a double coil in order to fit it all in a small 
space. That is, the filament is wound up to make one 
coil, and then this coil is wound to make a larger coil. In 
a 60-watt bulb, the coil is less than an inch long. 

Source:
Special thanks to Howstuffworks.com for the above
article. Visit Howstuffworks.com on the web for your 
education needs.