Version 10 Structure of the Atom

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As mentioned above, the proton carries a charge of posi­tive electricity. We know the bodies charged with the same kind of electricity to repel one another. When two protons are brought close together they repel one another with great force.

The second of these basic components of the nucleus is the neutron. The neutron does not carry a definite electric charge. The sub-particles that form the neutron do carry charges but the charge of one balances that of another, leav­ing the neutron neutral. It is from this state that it gets its name.

The third component of the atom is the electron. The elec­trons revolve around the nucleus. Each electron carries a negative charge, of electricity that is equal to the positive charge of a proton in the nucleus.

As the charge of the electron is negative and that of the proton positive it might be thought that the proton would attract the lighter electron and draw it into the nucleus. This would happen if the electron were not revolving around the nucleus.

Quiz

for the third-year students, 5^th term (EP, ES)

Prepared by A.V.Kosobokova

Version 11 Electron Theory

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The foundations of the modern theory of electricity were laid in the study of the electric discharge through gases, and in particular the so-called cathode rays. The nature of these cathode rays was first described by Crookes (1879) when he considered them as negatively electrified particles which were emitted from a metal under the influence of a strong electric field.

Further experiments made on these particles confirmed that they carried a negative charge and the name "electron" was given to them. It is the movement of the electrons, wheth­er in a conductor or a gas which gives rise to the phenomenon known as the electric current.

The student should remember that an electron, being nega­tively charged, will move towards that end of the circuit or that part which is termed "positive". The old conception of the electric current flowing from the positive pole or end of the circuit to the negative was accepted long before the ex­istence of the electron theory. It is in direct opposition to the real direction of electron flow. This conception is, however, too firmly established and the current is still assumed to flow from positive to negative.

Quiz

for the third-year students, 5^th term (EP, ES)

Prepared by A.V.Kosobokova

Version 12 Electron Theory

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The number of the electrons comprising the unit of cur­rent has been computed. At present, we know one microam­pere to be eqpal to the passage of 6 milliard electrons per second. To keep a 100-watt lamp burning requires a flow of six milliard milliard electrons – not in a day, nor an hour, but every second. Six milliard milliard means the figure six with eighteen zeroes after it.

We know electrical energy to change into light energy in the electric lamp. Can light energy be changed back to electrical energy?

The emission of electrons under the impact of light energy is called photoelectric emissjon. The more intense the light, the more electrons are emitted by the metal exposed to light. Although most metals will emit electrons when their surfaces are exposed to ultraviolet light, some metals, such as sodium, potassium, and certain others will emit electrons when ex­posed to ordinary visible light rays and infrared rays as well. The first discovery came in 1887 when Heinrich Hertz, the prominent German scientist, found out that for a given electromotive force an electric spark will jump across a larger gab.

Quiz

for the third-year students, 5^th term (EP, ES)

Prepared by A.V.Kosobokova