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Complete the sentences.



1. The frequency of visible light is referred to as.... 2. High frequency light has....3. Low frequency light has...4.Light waves come in a continuous variety of...5. The way different substances affect the speed at which light travels is...

Put questions to the following sentences.

1.Light waves come in many frequencies. 2. The amount of energy in a light wave is proportionally related to its frequency. 3. Light waves slow down when they travel inside substances, such as air, water, glass or a diamond. 4. Light waves come in a continuous variety of sizes, frequencies and energies.

Give the definitions.

Frequency, Hertz (Hz), light waves, refraction.

Retell the text.

Text 12

Producinga Photo

Vocabulary

electromagnetic - электромагнитный

sense, v - ощущать, чувствовать

collection - скопление

source - источник

produce - производить

object-предмет

now , v - течь

reflect - отражать

involve - включать в себя

nucleus - ядро, центр

distance - расстояние

a packet of energy - масса энергии

generate - порождать

sodium- натриевый

to accept- принимать

to emit —испускать

vapor – паровой

Any light that you see is made up of a collection of one or more photons traveling through space as electromagnetic waves. In total darkness, our eyes are actually able to sense single photons, but generally what we see in our daily lives comes to us in the form of millions of photons produced by light sources and reflected off objects. If you look around you right now, there is probably a light source in the room producing photons, and objects in the room that reflect those photons. Your eyes absorb some of the photons flowing through the room, and that is how you see.

There are many different ways to produce photons, but all of them use the same mechanism inside an atom to do it. This mechanism involves the energizing of electrons orbiting each atom's nucleus. How Nuclear Radiation Works describes protons, neutrons and electrons in some detail. For example, hydrogen atoms have one electron orbiting the nucleus. Helium atoms have two electrons orbiting the nucleus. Aluminum atoms have 13 electrons orbiting the nucleus. Each atom has a preferred number of electrons orbiting its nucleus.

Electrons circle the nucleus in fixed orbits a simplified way to think about it is to imagine how satellites orbit the Earth. There's a huge amount of theory around electron orbitals, but to understand light there is just one key fact to understand: An electron has a natural orbit that it occupies, but if you energize an atom you can move its electrons to higher orbitals. A photon of light is produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit. During the fall from high-energy to normal-energy, the electron emits a photon a packet of energy with very specific characteristics. The photon has a frequency, or color, that exactly matches the distance the electron falls.

There are cases where you can see this phenomenon quite clearly. For example, in lots of factories and parking lots you see sodium vapor lights. You can tell a sodium vapor light because it is very yellow when you look at it. A sodium vapor light energizes sodium atoms to generate photons. A sodium atom has 11 electrons, and because of the way they are stacked in orbitals one of those electrons is most likely to accept and emit energy (this electron is called the 3d electron). The energy packets that this electron is most likely to emit fall right around a wavelength of 590 nanometers. This wavelength corresponds to yellow light. If you run sodium light through a prism, you do not see a rainbow you see a pair of yellow lines.

The thing to note from this list is that anything that produces light does it by energizing atoms in some way.

Exercises:

1. Give Russian equivalents of the following phrases:

A collection of one or more photons, total darkness, to sense single photons, us in the form of millions of photons, the photons flowing through the room, a natural orbit, in a higher-than-normal orbit, a sodium vapor light, sodium atoms, to accept and emit energy, a pair of yellow lines, with very specific characteristics.







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