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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.