Science: light 1

Wavelength

-Distance from the top of one wave to the top of the next. -The shorter the wavelength, the more energy the wave carries.

Shadows

-If an object allows less than 100% of the light that hits it to pass through, then the object will cast a shadow. In reality this means that all objects will cast a shadow, since no object is perfectly transparent. If all of the light which hits an object went through it, you would not be able to see the object; you can only see objects because some light reflects from the object to your eye! In addition, as light passes through an object, some of the light will be absorbed. -It is easier to completely block all of the light if the light source is small. Shadows made by smaller light sources therefore have a lot of umbra. Large light sources are harder to completely block, so the shadow will have a bigger penumbra; in fact it might not even have an umbra!

Light will be...

-Light will be reflected, transmitted, absorbed -When light is absorbed, the electromagnetic energy changes to other kinds of energy. -Light can pass through transparent objects and some light can pass through translucent objects. Opaque objects do not allow visible light to pass through them.

Vapor Lamps

-These bulbs contain argon or neon gas and sodium. -When electricity flows to the bulb, it warms up and the sodium changes to vapor which becomes ionized. -After a few minutes, the vapor starts to emit yellow light. -Sodium lights are very efficient, turning almost all of the electrical energy to light. -The human eye is especially sensitive to yellow light, so it seems brighter to us than other colors at the same power.

Neon Lights

-These lights consist of a glass tube containing a gas such as neon, krypton, helium, argon. -The gas in the tube becomes ionized, allowing electricity to go through the gas. - This causes some electrons in the gas atoms to jump to a higher energy level in the atom. - Light is emitted when the electrons fall back to where they started. -The colors depend on which gas is in the tube.

Infrared Light

-all objects emit infrared light based on their temperature -burglar alarm systems us infrared light and to control security lighting outside homes. This detect the infrared emitted by people and animals -TV remote uses infrared light -Scientist are developing a way to find buried mines using infrared

Amplitude

-defined as the maximum displacement from the center of the wave -determines the intensity of the wave -bigger amplitude means that the wave has more energy -as a wave spreads out, the amplitude of the wave becomes smaller, as the energy is spread over greater area.

Frequency

-defined as the number of vibrations per second -a wave with a long wavelength has a low frequency -if the frequency of the wave is higher, it transfers more energy -depends on how much energy was involved in creating the wave

Ultraviolet light

-electromagnetic energy is absorbed by atoms it increases the vibration of the atom and/ or the tiny particles inside the atom -ultraviolet, x-rays, and gamma rays have more energy than other kinds of waves and can knock electrons away from the atoms, or cause molecules to split. These waves are called ionizing radiation -This results in a change in the chemical structure of the molecule. This change is especially bad for living organisms, as it can cause call damage and deformities by actually mutating their genetic code -Divided into 3 types: UVA, UVB, UVC according to how much energy they have. UVC most energetic -When skin is exposed to UVB, cells produce Vitamin D -Sunbeds also mit UVB, but too much can cause cancer

Cons to incandescent lights

-give off most of energy is form of heat-carrying infrared light, only 10% of the light produced is in the visible spectrum. This waste a lot of electricity. Cool light sources, such as florescent lamps and LEDs, don't waste a lot of energy generating heat, they give off mostly visible light. They are slowly edging out the old light bulbs

Incandescent light bulb structure

-have 2 metals contacts, connect to the ends of electrical circuit. the metal contacts are attached to 2 stiff wires, which are attached to a thin metal filament. sits in middle of bulb held up by a glass mount. The wires and the filament are housed in a glass bulb, filled with insert gas such a argon or nitrogen

Microwaves

-have shorter wavelengths than radio waves, but higher frequencies -microwaves with certain wavelengths are absorbed by water molecules and can be used for cooking. Water in the food absorbers microwave radiation, which causes the water to heat up and cook the food -radars use microwaves -cell phones use microwaves -waves used in cell phone have less energy per second then waves in microwave oven Doppler radar use microwaves to tell how fast the cloud/rain are moving toward the detector

Incandescent light sources

-light produced by a hot object -The atoms in the heated object vibrate more and some of this energy is changes to electromagnetic energy, As each particle has a different amount of energy depending on how much it is vibrating, the object produces every possible wavelength of light over a certain range of wavelengths (called continuous spectrum)

Luminescent light sources

-light produced without the need for heating -something causes electrons in some atoms to shift from their normal positions in the atom to a position further from the atom's nucleus. This atom is described as "excited". When the electrons drop back to its normal positions it releases electromagnetic energy -there are many different ways electrons can gain energy

Radio Waves

-longest wavelength and lowest frequencies in the electromagnetic spectrum -used to transmit television and radio programs -TVs use higher frequencies then radios -MRIs uses radio waves to produce images -Many objects in space emit radio waves -travel through clouds of space dust which block visible light -the study of radio waves helped to learn about space

The filament

-made up of a long, thin length of tungsten metal. The tungsten is arranged in a double coil in order to fit it all in a small space. the filament is wound up to make one coil, and then this col is wound to make a larger coil -Tungsten is used in nearly all incandescent light bulbs because it is an ideal filament material. Most metals melt before reaching the high temperatures. But tungsten has a very hight meting temperature. Tungsten can catch fire at really really high temperature. the filament the light bulb is sealed in a oxygen-fee container to prevent it from catching fire

Electromagnetic waves

-most not visible to humans because body can't detect waves -very narrow range of electromagnetic waves we can see, we call this visible light. We detect infrared light as heat, even though we cannot see it

Florescent Bulbs

-sealed in a glass tube coated with chemicals called phosphors. The tube is filled with mercury vapor and argon gas at low pressure. At each end of the tube there are electrodes with tungsten filaments -When the light is on one electrode heats up and releases electrons -theses electrons ionize the gas, so that electricity can flow through the gas -as electrons collided with the atoms of mercury, the mercury atoms produce UV light -the UV light collides with the phosphors in the chemical coating on the inside of the tube -The phosphors absorb the UV light and release visible light of a few specific wavelengths. We see the combination of these wavelengths as white

Light as a wave

-started by vibration of particles inside atoms -transfer energy -Light doesn't disturb that particles of the material, it can travel through empty space. Electromagnetic waves disturb force fields called electric and magnetic fields. A Magnetic field can produce an electric field which can produce a magnetic field. Fields constantly change as the wave travels -Ina vacuum all light waves travel at 300,000 Km/second (called speed of light). Light travels slower when it travels through materials then it does in a vacuum

X-Rays

-used to produce photos of bones to check for damage -can go through soft tissue but are blacked but bone and metal -used to in industry to check metal items for damage -Lead blanket used to prevent other parts of the body form being exposed to x-rays as high levels of exposure increase the risk of cancer -CT scans use x-rays -Airports use x-rays to look inside bags, 2 different ranges pf x-ray wavelengths are used, because some materials absorb more of the one or the other kinds of x-rays

halogen Light bulbs

-uses tungsten filament, but encased inside a much smaller container made pf quartz. Because the container is so close to the filament, it would melt if it was glass. The gas inside the container is a group of gases called halogens. They combine with tungsten vapor. If the temperature is high enough, the halogen gas will combine with tungsten atoms as they evaporate and redeposit them on the filament. This recycling process lets the filament last a lot longer. meaning you get more visible light per unit of energy. You still get a lot of heat, though; and because the quartz container is so close to the filament, it's extremely hot compared to a normal light bulb.

Characteristics of Light waves

-wavelength: varies from very long to very short wavelengths, light we can see has a wavelength of a millionth of a meter -Frequency: measured in Hertz(Hz) -Amplitude: determines intensity of light wave, the more energy per cm2, the brighter the light appears. Bigger amplitude means more energy that wave has. as light spreads, the amplitude of the wave becomes smaller and the light becomes less bright.(this is why light is dimmer if you are standing further away from the light source.

Microwave ovens

-waves produced by a device called magnetron which changes electrical energy to microwaves . -absorb water, fats and sugars. Not absorbed by most plastics, glass or ceramics. Metal reflects microwaves. This is why the walls are metal. -In a regular oven, the heat has to transfer(by conduction) from the outside of the food toward the middle hot, dry air on the outside of the food evaporates moisture, so the outside can be crispy and brown while the inside is moist In microwave cooking, the microwaves penetrate the food and excite water and fat molecules pretty much evenly throughout the food. No heat has to transfer toward the middle by conduction. There's heat everywhere all at once because the molecules are all excited together as long as the piece of food is not too thick. In a microwave oven, the air in the oven is at room temperature, so there's no way to form a crust. That is why microwavable pastries sometimes come with a little sleeve made out of foil and cardboard. You put the food in the sleeve and then microwave it. The sleeve reacts to microwave energy by becoming very hot. This exterior heat lets the crust become crispy as it would in a regular oven.

How incandescent light bubbles work

-when the bulb is hooked up to to a power supply, an electric current flows from one contact to the other, through the wires and the filament. An electric current is movement of the particles called electrons. 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 up the filament -Metel atoms release mostly infrared light. But if heated at a high enough level, around 2,200 C , they will produce a good deal of visible light

Ray

A thin beam of light is often called a ray. Any beam of light, no matter how wide, can be thought of as a bundle of rays. When light shines on an object some of the rays pass by the object and some rays are reflected or absorbed. The area which is not reached by rays is called the shadow. The shadow is always there, but it cannot always be seen. You can only see a shadow if something acts as a screen behind the object.

How the incandescent light will stop working

At extreme temperatures, some of the tungsten atoms vibrate with enough energy to detach from the atoms around them and go into the air. This is evaporation. As more and more atoms evaporate, the filament starts to disintegrate. The evaporated atoms are carried upwards by convection currents in the gas and are deposited on the glass which started to get darker. Eventually, the filament will become too thin and break

Do CFLs contain mercury?

Do CFLs contain mercury? CFLs contain a very small amount of mercury sealed within the glass tubing - an average of 4 milligrams. Most mercury vapor inside fluorescent light bulbs becomes bound to the inside of the light bulb as it is used. EPA estimates that the rest of the mercury within a CFL - about 14 percent - is released into air or water when it is sent to a landfill, assuming the light bulb is broken. Therefore, if all 290 million CFLs sold in 2007 were sent to a landfill (versus recycled, as a worst case) - they would add 0.16 metric tons, or 0.16 percent, to U.S. mercury emissions caused by humans. Because CFLs also help to reduce greenhouse gasses, other pollutants associated with electricity production, and landfill waste (because the bulbs last longer), they are clearly the environmental winner when compared to traditional incandescent light bulbs.

What should I do with a CFL when it burns out?

EPA recommends that consumers take advantage of available local recycling options for compact fluorescent light bulbs. If your state or local environmental regulatory agency permits you to put used or broken CFLs in the garbage, seal the bulb in two plastic bags and put it into the outside trash, or other protected outside location, for the next normal trash collection.

Led Lights

LEDs are made of materials called semiconductors which produce light when electricity passes through them. White light is a combination of different wavelengths, so one LED cannot produce white light. Some white LEDs use phosphors to change ultraviolet light into other wavelengths which together appear white. In other appliances, red, blue and green LEDs are combined, because this combination of light appears white to human eyes. LEDs were once expensive to produce, but the price is dropping each year. They use even less electricity than fluorescent bulbs and are very bright. Manufacturers claim that they will last about 25 years, but this kind of bulb is quite new, so no one has had one for 25 years to find out!

Why should people use CFLs

Making this change will help to use less electricity at home and prevent greenhouse gas emissions that contribute to global climate change. Lighting accounts for close to 20 percent of the average home's electric bill. ENERGY STAR qualified CFLs use up to 75 percent less energy (electricity) than incandescent light bulbs, last up to 10 times longer, cost little up front, and provide a quick return on investment. CFLs produce about 75% less heat, so they are safer to operate and can cut energy costs associated with home cooling If every home in America replaced just one incandescent light bulb with an ENERGY STAR qualified CFL, in one year it would save enough energy to light more than 3 million homes. That would prevent the release of greenhouse gas emissions equal to that of about 800,000 cars. In 2007, Americans saved $1.5 billion by switching to ENERGY STAR qualified CFLs. The energy saved could light all the households in a city the size of Washington, DC for over 30 years. Put another way, changing these bulbs removes as much greenhouse gas pollution as planting 2.85 million acres of trees or taking 2 million cars off the road each year.

The 2 parts of a shadow

Shadows have two parts; an inner section which is darker (the umbra) and a lighter outer section (the penumbra). No light at all reaches the umbra. The penumbra or partial shadow is where light from some parts of the light source can reach, but light from other parts of the light source cannot.

Solar eclipse

Solar eclipses happen when the moon gets between the earth and the sun in a position where the earth is in the moon's shadow. The moon is a small object compared to the earth, so its shadow is small compared to the earth. The shadow of the moon only just reaches the earth. If you stand in the umbra of the moon's shadow, no light from the sun will reach you and you will experience a total solar eclipse. You are very unlikely to be lucky enough to be in the umbra because it is a very small area compared to the size of the earth and it is much more likely to be cast on an ocean or a desert than on your town, simply because a lot of the earth's surface is water and desert! The earth, sun and moon only line up in just the right positions about twice a year. If you happen to be in the penumbra of the shadow, and you look up you will see only a part of the sun. Light from some parts of the sun is being blocked by the moon, so you only see the parts of the sun from which light is reaching the earth. What you see is called a partial solar eclipse. The penumbra covers a bigger area, so you are more likely to see a partial eclipse.

Speed

The speed of a wave describes how fast the disturbance is through the medium. This is *not* the same as how fast the medium is vibrating -depends on the material that it is going through

How do waves start?

Waves begin with some kind of disturbance and travel through the material because one part of the medium affects the behavior of the next part of the medium, and so on.

UVC

able to directly disable the strands of DNA in bacteria and viruses and make them inert -inactive bacteria and viruses= dead because can't reproduce and multiply -the ability of UVC to inactive bacteria and viruses is used to sterilize surfaces of things such as medical equipment

Mechanoluminescence

atoms gain energy from mechanical changes such as rubbing the materials

Electroluminescence

atoms get energy from an electrical current

Chemiluminescence

atoms get energy from chemical reactions

Photoluminescence

atoms take in electromagnetic energy. Which may be transformed to a kind of electromagnetic energy with less energy. Atoms may emit the light immediately, a process called fluorescence, or over a period of time, in which case the process is called phosphorescence

Lunar Eclipses

happens when the earth gets between the moon and the sun, so that the shadow of the earth falls on the moon. Lunar eclipses happen during the full moon. The earth's shadow is large compared to the size of the moon, so the entire moon can easily fit into the earth's shadow. When the moon is in the umbra of the earth's shadow, no light from the sun reaches the moon, so no light reflects back from the moon to the earth, and the moon cannot be seen. When the moon is completely in the umbra, we see a total lunar eclipse. When the moon is only partly in the umbra we see a partial lunar eclipse. When the moon is in the penumbra each part of the moon's surface receives some light, so although the moon may look a bit dimmer, you can still see it. When a lunar eclipse occurs, anyone who is on the side of the earth facing the moon can see it.

Light can be thought of... or as a ...

light can be thought of as a wav or as a stream of particles

Gamma Rays

radiations is produced by changes in nucleus of atoms -occurs in nuclear power plants, nuclear explosions and when radioactive materials change -very high frequency and energy -can be use to kill dangerous bacteria in food. This is called irradiation, also makes food last longer before it goes bad. -can be use dot kill cancer cells but high dose can cause cancer -knife treatments involve shooting many low intensity beams of gamma ray at a tumor from different angles, so that they all meet at the tumor

Intensity

the energy per unit of area

Bioluminescence

the productions of light by chemical reactions in living organisms

All waves transfer energy...

without transferring the material through which the wave is traveling