Unit 2 An Electrical Circuit and Its Elements

An electrical circuit is a combination of devices for running an electrical current. Electromagnetic processes can be described in such terms as current, voltage (potential difference) electromotive force, charge, magnetic flux, resistance, inductance, mutual inductance and capacitance.

The main elements of a circuit are sources and loads of electrical energy (signals).

The power sources and signal sources are intended for converting various kinds of energy into electrical energy (turbo and hydrogenerators, accumulators, electron generators, etc.).

The loads of energy (signals) are used for converting electrical energy into other kinds of energy (electrical motors, electrical furnaces, electron-beam tubes, etc.).

Besides these main elements, the circuit contains various auxiliary elements, which connect sources with loads (lines of transmission, connective wires), suppress or strengthen certain components of the signal (filters, amplifiers), charge the magnitudes of voltages and currents (transformers) and so on.

There are two kinds of circuits: the first circuits are intended for transmitting and converting electrical energy (these circuits are used in electro-power engineering) and the second circuits are intended for transmitting and transforming information (these circuits are used in communication engineering, radio engineering, devices of automation and telemechanics, etc.).

Each element of a circuit has a certain number of terminals (poles) in order to connect this element with other elements. Two-pole elements have two terminals. Power sources (except multiphase sources), resistors, capacitors, inductance coils are two-pole elements. Three-pole elements are electron lamps (vacuum triodes) and transistors (semiconductive triodes). Four-pole elements are two-winding transformers, integral operational amplifiers. The elements of a circuit having more than four terminals are multiwinding transformers, various micro-modules, solid-state components of electron schemes, etc. Three-pole, four-pole elements and so on are called multipole elements.

We distinguish active and passive elements of a circuit. The power and signal sources are active elements. We also consider electron lamps, transistors, operational amplifiers as active elements, which are capable to strengthen an electrical signal. The energy is dissipated or accumulated (resistors, inductive coils, capacitors, transformers) in the passive elements.

Ex.1. Answer the questions.

1. What is an electrical circuit?

2. What terms are used to describe an electromagnetic process?

3. Can you give definitions to the words “current, voltage, charge, resistance”?

4. What are the main elements of a circuit?

5. What is the function of power sources?

6. What are the loads of energy used for?

7. What do auxiliary elements serve for?

8. What is the difference between two kinds of circuits?

9. Name the examples of two-pole and three-pole and four-pole elements.

10. What are the examples of active and passive elements of a circuit?

Ex.2. Match the words (1-9) with their definitions in (A-I).

1. current, 2.electrical load, 3.resistance, 4.transformer, 5.charge, 6.amplifier, 7.capacitor, 8.inductive coil, 9.transistor.

A. a coil which is used to produce electromagnetic induction;

B. the amount of stored electricity an object holds;

C. the amount of voltage applied on two resistor terminals compared to the current that circulated between them;

D. the quantity of electricity that is flowing in a wire at a specific time;

E. a device with three terminals which can be used as an amplifier or switch;

F. a device that changes electricity from high to low voltage;

G. a device which increases the amplitude (wave height) of the current;

H. the total amount of power, or amperage;

I. a device which allows a certain amount of electric charge to be stored.

Ex.3. Complete the text about inverters using the words in the box.

frequency, direct current, alternating current, sine wave, single-phase, hertz, electricity