Electrical currents and their properties

I. Read and learn the following words.

is made up of tiny crystals – складається з крихітних кристалів
namely – а саме
regular and orderly arrangement – вірне розташування атомів
a wire – дріт
at random – безпорядкові
electromotive force – електрорухома сила
direct current – постійний струм
alternating current – перемінний струм
free electrons – вільні електрони

II. Read and translate the text

Conduction is the name normally given to a movement or flow of charges. The charges are usually electrons, but may also be ions when the conduction takes place in gaseous or liquid conductors, in which the ions are mobile.

How does the current flow through a wire? A metal is made up of tiny crystals which are visible under a microscope. A crystal is a regular and orderly arrangement of atoms. As it was explained, an atom is a complex particle in which tiny electrons move around nucleus. When the atoms are tightly packed as they are in a metallic solid, some of the electrons move freely between the atoms. These are called free electrons.

Ordinarily, the free electrons move at random through the metal. There must be some driving force to cause the electrons to move through the metal conductor. This driving force tending to produce the motion of electrons through a circuit is called an electromotive force or e. m. f. that moves electric charges from one point in the circuit to another.

When an electromotive force is applied to the ends of a wire the free electrons move in one direction. It is the movement of the free electrons in a conductor that induces an electric current. The greater the number of participating electrons, the greater is the flow of current.

No one has ever seen an electric current. We only know of the existence of a current by its effects. A current can heat a conductor, it "can have a chemical action when passing through a solution, or it can produce a magnetic effect. We can measure currents by observing their heating, their chemical, or their magnetic effects. There are some kinds of current, namely: a direct current (d. c, for short), an alternating current (a. c), a pulsating current.

III. Get ready to answer the following questions:

1. What is conduction?
2. How does the current flow through a wire?
3. How are the atoms packed in solids?
4. What is called an electromotive force?
5. How can a conductor induce an electric current?

IV. Continue the sentences.

1. The charges are usually ………… .
2. A crystal is a ………………… .
3. When the atoms are tightly packed ……………… .
4. The free electrons ………… .
5. When an electromotive force is applied to ……………… .
6. A current can heat …… .