G azərbaycan respublikasi təHSİl naziRLİYİ azərbaycan texniKİ universiteti M. M. QƏNDİLova e. Q. İsmayilova



Yüklə 0,69 Mb.
səhifə238/366
tarix10.01.2022
ölçüsü0,69 Mb.
#106324
növüDərs
1   ...   234   235   236   237   238   239   240   241   ...   366
JOKES, LAUGHS, SMILES
“A telegram from George, dear.”

“Well, did he pass the examination this time?”

“No, but he almost at the top of the list of those who failed.”

UNIT XIV
Nothing is impossible to a

willing heart

Heywood, John
MOLECULES, ATOMS AND FREE ELECTRONS
All matter is made up of molecules, which are made up of atoms, the smallest unit division of an element (an individual substance not made up of other substances). An atom consists of a heavier central nucleus with very small electrons revolving around it. An electron exhibits a quality called negative charge and has a mass that is no more than a very small fraction of a gram. The nucleus of an atom contains protons and neutrons have no electrical charge, but they contribute to the mass of the atom. Other particles and forces exist in the nucleus that affect the behavior of the atom. Atoms of different elements have different number of protons, neutrons, and electrons, but in an electrically neutral atom- one that is neither positively nor negatively charged the number of protons equals the number of electrons. The number of protons and electrons is different for each of the elements: an atom is hydrogen has one proton and one electron, helium has two, oxygen has eight, and uranium has 92 protons and 92 electrons.

The electrons rotate around the nucleus in groups called rings, or shells. For example, in the copper atom the inner ring has two electrons, the second has eight, the third has 18, and the outer ring that is of interest in the study id electricity. It is so loosely bound to the nucleus that it can migrate from one atom to another and is called a free electron.

Normally, an atom is electrically neutral, with the same number of electrons as protons. However, if an atom should lose an electron to another atom, then it has one more proton than electrons and is said to have a positive charge. The atom is now in an abnormal condition and will exert a force to obtain an electron from some other atom in order to restore its state of electrical neutrality. The positively charged atom will pick up an electron from a neighboring atom, which will restore its electrical balance by attracting an electron from a third atom, and so on.

Some materials have a large number of free electrons and other materials have very few. Copper, for instance, has 1.641024 free electrons per cubic centimeter, making it a very good conductor of electricity. Rubber, on the hand, has only three or four free electrons per cubic inch and is called a nonconductor or insulator. In a nonconductor, all electrons are very tightly bound to the nucleus. The flow of electric current does not depend on how fast the free electrons move from one to another, but on how many electrons move past a point in a given amount of time.



Yüklə 0,69 Mb.

Dostları ilə paylaş:
1   ...   234   235   236   237   238   239   240   241   ...   366




Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©muhaz.org 2025
rəhbərliyinə müraciət

gir | qeydiyyatdan keç
    Ana səhifə


yükləyin