Introduction to the World of Nuclear Physics. Lidiya Strautman

charges repel, unlike charges attract

      Two electrons will tend to repel each other because both have a negative electrical charge. Two protons will also tend to repel each other because they both have a positive charge. On the other hand, electrons and protons will be attracted to each other because of their unlike charges.

      Since the electron is much smaller and lighter than a proton, when they are attracted to each other due to their unlike charges, the electron usually does most of the moving. This is because the protons have more mass and are harder to get moving. Although electrons are very small, their negative electrical charges are still quite strong. Remember, the negative charge of an electron is the same as the positive electrical charge of the much larger in size proton. This way the atom stays electrically balanced.

      Another important fact about the electrical charges of protons and electrons is that the farther away they are from each other, the less force their electric fields have on each other. Similarly, the closer they are to each other, the more force they will experience from each other due to this invisible force field called an electric field.

THE FREE ELECTRON

      Maintaining electrical balance

      Each basic element has a certain number of electrons and protons, which distinguishes each element from all other basic elements. In most elements, the number of electrons is equal to the number of protons. This maintains an electrical balance in the structure of atoms since protons and electrons have equal, but opposite electrostatic fields.

      Pictured here is an atom of copper, which is much more complex than either an atom of hydrogen or helium.

      The copper atom has 29 protons in its nucleus with 29 electrons orbiting the nucleus. Notice that in the copper atom, the electrons are arranged in several layers called shells. This is to graphically represent that the electrons are at different energy levels within the atom. The energy of an electron is restricted to a few particular energy levels. The energy is said to be quantized, meaning that it cannot vary continuously over a range, but instead is limited to certain values. These energy levels or shells follow a very predictable pattern. The closest shell to the nucleus can have up to 2 electrons. The second shell from the nucleus can have up to 8 electrons. The third shell can have up to 18 electrons. The fourth shell can have up to 32 electrons, and so on. Atoms can have this many electrons, but they do not have to have this many electrons in each shell. The greater distance between the electrons in the outer shells and the protons in the nucleus means the outer shell electrons experience less of a force of attraction to the nucleus than do the electrons in the inner shells.

EXERCISES

      Ex. 1. Make the following sentences negative.

      1. Each basic element has a certain number of electrons and protons, which distinguishes each element from all other basic elements. 2. These materials are called insulators. 3. The third shell can have up to 18 electrons. 4. This way the atom stays electrically balanced. 5. Although electrons are very small, their negative electrical charges are still quite strong.

      Ex. 2. Make up questions to which the following sentences are the answers.

      1. The closest shell to the nucleus can have up to 2 electrons. 2. In most elements, the number of electrons is equal to the number of protons. 3. This positively charged electrostatic field is exactly the same strength as the electrostatic field in an electron, but it is opposite in polarity. 4. Two electrons will tend to repel each other because both have a negative electrical charge. 5. Another important fact about the electrical charges of protons and electrons is that the farther away they are from each other, the less force their electric fields have on each other. 6. Many materials do not have any free electrons.

      Ex. 3. Translate the sentences using the examples given below.

      The hypothesis proposed agreed with the experimental observation. – > The hypothesis which is (was) proposed agreed with the experimental observation. Предложенная гипотеза согласовывалась с экспериментальными наблюдениями. For some time scientists remained interested in the problem. В течение некоторого времени ученые сохраняли интерес к этой проблеме. 1. The method applied increased the accuracy of the results. 2. After a heated discussion the laboratory applied the method improved by Dr. N. 3. The scientist theoretically predicted complicated interaction between the components involved in the process. 4. At that time the problem presented increased danger of radioactive contamination and encountered opposition at most laboratories concerned. 5. The hypothesis concerned synthesized materials and did not apply to natural products. 6. Heat resistant materials developed in the last decade produced a revolution in a number of industries. 7. Automatized information processing radically modified the method devised. 8. The crystal produced revealed cracked faces.

      Ex. 4. Identify the element described by which-clause and give Russian equivalents of which.

      1. After Von Neuman's tragic death the computer project was abandoned, which was most unfortunate for Princeton. 2. It is impossible to make a complete list of things which physicists may find interesting to do in the coming decade. 3. This idea, which was wrong at that time, is no less wrong today. 4. The other disastrous thing seems to be a real danger, which can be avoided if we stayed diversified. 5. This technique was borrowed from physics, which is rather typical of the present-day biology. 6. The scientists expected the experiment to be completed by the end of the month, which would allow them to participate in the symposium. 7. That this comes out to be the case is a conclusive proof of the correctness of the theory. 8. What is still doubtful is the details, which does not prevent the theory from being useful, however.

      Ex. 5. Fill in the blanks with the appropriate words from the list given below.

      1. The sun … in its axis once every 27 days. 2. The … of light is expressed in meters per second. 3. The … solar day is the average length of the solar days in a year. 4. Hydrogen is the … element in all the stars. 5. If a pound of matter could be entirely converted into energy, the amount of energy would be … to the burning of 1,500,000 tons of coal. 6. The so-called polar wandering in which the earth's … actually remains fixed in its direction in space while the earth's matter moves around it has been explained. 7. Just as … revolve about the sun, there are bodies called moons revolving in orbits about their planets. 8. Mars is very small and its gravitational … is very weak. 9. … are caused by the attraction of the moon. 10. The diameters of these islands … from only a few hundred feet to about ten miles.

      1) tides, 2) planets, 3) predominant, 4) equal, 5) range, 6) rotates, 7) pull, 8) axis, 9) speed, 10) mean

      Ex. 6. Give English equivalents of the sentence using that, which or what.

      1. To, что это действительно происходит, неудивительно. 2. Трудно понять, что происходит в этот момент на самом деле. 3. То, что происходит в действительности, нельзя объяснить на основе этой гипотезы. 4. В этот момент температура резко повышается, что трудно объяснить на основе этой гипотезы. 5. В этот момент они увидели то, что ученые наблюдают очень давно, хотя и не могут объяснить природу этого явления. 6. Он при-водил много фактов из жизни разных ученых, что делало его лекции очень интересными.

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      What