Материал: Гвоздева Пхысицс фор адванцед студентс 2011
7. essentially
III. Make the sentences sound less categorical using S + seem (appear) + to V; S + do (does) not seem (appear) + to V
1.Neither the initial conditions, nor the values of the parameters in the theory are arbitrary.
2.Both the initial conditions and the values of the parameters are somehow chosen very carefully.
3.There is a very large number of different, separate universes with different values of the physical parameters and different initial conditions.
4.Most of these universes do not provide the right conditions for the development of the complicated structures needed for intelligent life.
CLASS EXERCISES
Exercise 1 (in groups)
Sharing ideas
Follow the passage.
1.Why do stable nuclides exist?
2.Why do elements exist?
3.Where are nuclides built up?
4.Why do stars exist?
5.How were stars formed?
6.Why does the universe exist?
7.What does one of the versions of the anthropic principle state?
8.What makes the existence of intelligent human species on the earth possible?
Exercise 2 (do it yourself)
Translate the sentences, then compare your translation with the original sentences and make corrections, if any.
1.Теоретически ни начальные условия, ни значения параметров не являются произвольными.
2.Согласно принципу энтропии существует множество вселенных с различными значениями физических параметров и различными начальными условиями.
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3.На большинстве этих вселенных не созданы те условия, которые нужны для развития сложных, разумных структур.
4.Для развития разумной жизни нужны условия и параметры, соответствующие нашей вселенной.
A NUMBER PROVIDED BY NATURE
Run through the passage and say what Paul Dirac thinks about dimensionless numbers.
“The large numbers hypothesis concerns dimensionless numbers provided by nature. An example of a dimensionless number is the ratio of the mass of the proton to the mass of the electron. There is another dimensionless number which connects Planck’s constant and the electronic charge. This number is 137, quite independent of the units. When a dimensionless number like that turns up, a physicist thinks there must be some reason for it. At present one cannot set it up.
There is another dimensionless number which is of importance. If you have an electron or a proton, the electric force between them is inversely proportional to the square of the distance; the gravitational force is also inversely proportional to the square of the distance. The ratio of those two forces does not depend on the distance. The ratio gives you a dimensionless number. That number is extremely large, about ten to the power thirty-nine. It’s a number provided by nature and we should expect that a theory will some day provide a reason for it.”
Paul Dirac
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Part IV. NUCLEAR ENGINEERING
UNIT 1
LASERS
Lasers show up in an amazing range of products and technologies. You will find them in everything from CD players to dental drills, from high-speed metal cutting machines to measuring systems. They all use lasers. But what is a laser? And what makes a laser beam different from that of a flashlight?
PRE-READING TASK
Give Russian correspondence:
once (as soon as, when), eventually (finally), to control (to regulate), the way (how), although (though), in general (ant. in particular), versus (against, as opposed to), after, in the form, specific (certain, particular), in contrast (visi versa), operation (work), in terms of (in view of), N + that
ABSORBTION OF ENERGY
Study the text. Mind the underlined grammar points.
An atom absorbs energy in the form of heat, light, or electricity. Once an electron moves to a higher energy orbit, it eventually wants to return to the ground state. When it does, it releases its energy as a photon – a particle of light. You can see atoms releasing energy as photons. For example, the heating element in a toaster turns bright red because atoms, excited by heat, release red photons. A picture on a TV screen is made up by phosphor atoms emitting light of different colors. Flashlights, fluorescent lights and, incandescent bulbs produce light because electrons change their orbit and release photons.
THE LASER
A laser is a device that controls the way energized atoms release photons. “Laser” is an acronym for light amplification by stimulated emission of radiation. Although there are many types of lasers, all of them
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have some common essential features. In a laser, the lasing medium is pumped to excite the atoms. For the laser to work efficiently it is necessary to have a large collection of atoms in the excited state. In general, the atoms are excited to a level that is two or three levels above the ground state. This increases the degree of population inversion. The population inversion is the number of atoms in the excited state versus that in the ground state.
After the electron absorbed the amount of energy necessary to reach the excited level, it releases this energy. The emitted energy comes out in the form of photons. The emitted photon has a specific wavelength (color) that depends on the energy state of the electron when the photon is released. Two identical atoms with electrons in identical states will release photons with identical wavelengths.
PROPERTIES OF LASER LIGHT
Laser light is different from normal light. Laser light has the following properties:
1.It is monochromatic. It contains one specific wavelength of light (one specific color). The wavelength of light is determined by the amount of energy released when the electron drops to a lower orbit.
2.It is coherent. It is ‘organized’ – each photon moves in step with the others. This means that the wave fronts of all the photons launch in unison.
3.It is directional. Laser light has a very tight, intense and concentrated beam, because photon emission is stimulated. In contrast, a flashlight releases photons randomly, which makes its beam weak and diffuse.
The wavelength of the photon depends on the energy difference between the excited state and the ground state. Stimulated emission occurs when a photon encounters another atom with the electron in the same excited state. The first photon would stimulate or induce atomic emission in such a way that the photon emitted from the second atom vibrates with the same frequency and direction as the incoming photon.
The other key to a laser operation is a pair of mirrors, one at each end of the lasing medium. Photons reflect off the mirrors to travel back and forth through the lasing medium. In the process, they would stimulate other electrons to energy transition and would cause the emission of
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more photons of the same wavelength and phase. The mirror at the end of a laser is half-silvered, meaning it reflects some light and lets some light through. The light that it lets through is the laser light.
Vocabulary Notes
1.an incandescent bulb is made of glass and gives out light when electricity passes through it.
2.to amplify – to increase intensity
3.to stimulate – (here) to excite – to induce – to cause the emission of photons
4.identical – similar – things that are identical are exactly the same
5.to encounter – to meet with
6.the frequency of a light wave is the rate with which it vibrates.
POST-READING TASK
(To be done at home in writing) I. Speak about.
1.a photon
2.a picture on a TV screen
3.an incandescent bulb
4.the population inversion.
5.colors
6.The wavelength of a photon
7.the common features all lasers have
II. What does it mean?
1.The laser light is monochromatic.
2.The laser light is coherent.
3.The laser light is directional.
III. Formulate questions.
1.The wavelength of the photon depends on …….. (What?)
2.Stimulated emission occurs …………………...... (When?)
3.The first photon would stimulate atomic emission in such a way ……. (In what way?)
4.The two mirrors are placed …………….. (Where?)
5.The mirror at the end of a laser is half-silvered. (Why?)
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