Vocabulary

electronic device електронний прилад

flow, current струм

conductor провідник

fields of force силове поле

randow movement хаотичний рух

drift плинути

terminal клема

voltage напруга

electromotive force електрорушійна сила

displace витісняти, заміщати

excess надмір, надлишок

deficiency нестача

source джерело (струму)

broken circuit розірванe коло

path шлях

power supply джерело енергії

Text 2

1. Read, entitle the text and show your attitude to its content.

In 1827 George Simon Ohm discovered that the amount of current which flows in a circuit increases if the potential applied is increased, and decreases if the resistance of the circuit is increased. His findings are known as Ohm’s law which states that the current in a circuit is directly proportional to the applied potential and inversely proportional to the resistance. The proportionality constant is the electrical resistance.

Resistance =

Symbolically, Ohm’s law is often written

R = , or 1 ohm = .

Using Ohm’s law is of great importance because of its being generally applied to so many electrical phenomena. One of its simplest applications is using a dry cell directly connected by wires to a small light bulb. The battery maintains a potential difference of 1.5 volts across the lamp. The electron current flowing through the circuit being 0.5 ampere, the resistance of the circuit is

R = = 3 ohms.

Although electromotive force and potential difference are both

measured in volts there is a real distinction between them. Electromotive force is defined as the work per unit charge done by the battery or generator on the charges in moving them around the cirquit. Potential difference between two points is defined as the work per unit charge done by the charges in moving from one point to the other.

If any two of the three quantities: resistance, current and potential difference are known for a curcuit, the third can always be determined by substituting in Ohm’s law. In other words, any one of the three factors may be the unknown, and Ohm’s law may be written in any one of three ways:

I = , R = , V = IR

Resistance is the property of an elec­tric circuit to convert power from electrical form to heat. The resistance of a circuit element, expressed in ohms, can be computed from the following formula, which gives the power P, in watts, converted into heat by a resistance of R ohms, when a current of effective value / amperes flows through the die element:

P = RF, or R = P/P.

This conversion is the basis of all resistance-type electric heating devices, including electric water heaters, electric resistance furnaces or space heaters, electric ranges, and electric hair dryers. A component connected into an electric circuit to provide resistance, with no reactance, is called a resistor.

Notes. D.C. current – direct current постійний струм.

А. С. current – alternative current змінний струм.

P – power of electric current, measured in watts.

R - resistance to electric current, measured in ohms.