Download Light - FT HELP

Light
Good morning ladies and gentleman, welcome to my presentation about light. I
hope you enjoy this. Let’s start!
At the begining I will explain some basic terms. The fisrt term is ‘light’. What is
light? It's a kind of energy called "electromagnetic radiation", but this kind of
radiation is not harmful, except for an occasional sunburn. There are other kinds
of electromagnetic radiation too (radio waves, microwaves, x-rays, etc.), but
light is the part WE can see, the part that makes the rainbow. It’s velocity is
about 3 million kph. For example light from the sun takes about 8 minutes to go
to earth.OK, the second term is ‘laser’. It is a special source of light of only one
pure color (or WAVELENGTH). You can't break up laser light into other colors
like white light. OK, the third term is ‘white light’. White light is regular light
from the sun or from a light bulb. You can split it up to see all the colors of
rainbow. How can you split it up? Yeah, it’s simple. You can split it up with a
prism. Raindrops also act like a tiny prism when they make a rainbow in the sky.
OK that’s all for the beginning, let’s go further.
In this part of my presentation I will tell you about controlling the light, lenses
and about lasers. Well, I will start with topic How we control the light. There are
3 basic ways how controlling the light. First, we can block it with something –
this make shadow. Second, we can reflect it, it means change its path with
mirror. And third way how controlling the light, we can bend it, it means change
its direction by making it pass into another transparent material of different
density, like glass or water. There are actually other ways to bend or deflect
light, including diffraction gratings and holographic lenses. These depend on
the wave nature of light, and are a little more difficult to explain. Scientists
have also found that gravity can bend light, but it takes a very large object with
strong gravity such as a star to bend light very much, so it's not an effect you see
every day! This is called REFRACTION, and it's how lenses work. Now I will
explain what is lenses. Lenses bend light in useful ways. Most devices that
control light have one or more lenses in them (some use only mirrors, which can
do most of the same things that lenses can do). There are two basic simple lens
type: CONVEX or POSITIVE lenses will CONVERGE or FOCUS light and can
form an IMAGE and CONCAVE or NEGATIVE lenses will DIVERGE, it
means spread out, light rays. You can have mixed lens shapes too. Simple lenses
can't form very sharp images, so lens designers or optical engineers figure out
how to combine the simple types to make complex lenses that work better. We
use special computer programs to help us do this because it can take BILLIONS
and BILLIONS of calculations. Complex lens are for example in camera or
video camera. OK, we can use convex lense as magnifying glass. This diagram
shows how a magnifying glass bends light rays to make things look bigger than
they are. Many optical devices use the same basic idea of bending the light to
fool your eye and brain so light LOOKS like it came from a different (usually
larger or closer) object. OK, now I will tell you something about laser. Laser is,
as I mentioned at the beginnig of my presentation, a special source of light of
only one pure color (or WAVELENGTH). You can't break up laser light into
other colors. Lasers can be focused to a very small spot and can shine for long
distances without spreading out very much (unlike a flashlight which spreads
out a lot). The spot contains a lot of energy - so much that some lasers can cut
through thick metal (and smaller ones are used as scalpels in some kinds of
surgery). Lower-power laser systems can be used to send and pick up
information. For example, the product code scanner in a supermarket uses a
laser, lenses, rotating mirrors, and a computer to "read" bar codes from products.
And the tiny laser in a CD player reads EVEN tinier bumps and holes that
record the music like Morse Code (bumps and holes are used something like
dots and dashes). Lasers can also send information through long threads of glass
called OPTICAL FIBERS. A single laser can send thousands of phone
conversations through a fiber at the SAME TIME. Lasers are also used to make
3-D pictures called HOLOGRAMS (some engineers are working on moving
holograms, so someday we may have AMAZING 3-D TV pictures.
Q:Why can CD split light up like raindrops?
A:Because CD has fine grooves like a diffraction grating or a hologram.