Circuits and components

Electric circuits are made of interconnected components. There are two categories in the classification of components: active and passive. Passive elements never supply more energy than they absorb, while active elements can supply more energy than they absorb. Active elements are: cells, batteries, generators, electron tubes, transistors, etc. Passive components include resistors, capacitors, inductors, relays, fuses, switches, etc.

There are several different devices that can supply the voltage necessary to generate an electric current. The two most common sources are generators and cells.

Generators are machines that convert mechanical energy into electrical energy. They use mechanical energy, such as water pouring through a dam or the motion of a turbine driven by steam, to produce electricity. The electric outlet on the walls of homes and other buildings are connected to giant generators located in electric power stations. Each outlet contains two terminals. The voltage between the terminals drives an electric current through the appliance that is plugged into the outlet.

A cell is an electric storage device, containing chemicals which supplies a direct current. Several cells connected together are called a battery. A battery is a device that converts chemical energy directly into electrical energy. It consists of a number of voltaic cell. Chemical reactions within a battery produce a potential difference between the cell terminals.

There are many sources of electric current other than generators and batteries. Fuel cells, for example, produce electricity through chemical reactions.

An electron tube (or vacuum tube) is a device used to control the flow of electricity in a circuit. It is used for rectification, oscillation, amplification, switching or creation of electrical signals.

A transistor is a solid-state electronic component used to regulate a current passing through them. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A transistor can act as an oscillator, amplifier, photocell or switch. Unlike electron tubes, transistors operate on small amounts of power.

A resistor is a two-terminal electronic component which implements electrical resistance as a circuit element. Resistors are common elements of electrical networks and electronic circuits and are in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire. Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits. Thus, resistors are components in an electric circuit that are used to introduce resistance to a current. Resistors can be fixed and variable.

A thermistor is an electrical device whose resistance decreases as its temperature increases.

A diode is a device with two terminals which allows current to flow in one direction only. A photodiode is a light sensitive diode; a semiconductor which allows electricity to pass through it depending upon the level of light falling on it.

A capacitor (formerly known as a condenser) is a device used in electronic circuits for storing electric charge. It is a passive electronic component consisting of a pair of conductors separated by a dielectric (Fig. 4). An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. Fig.4. Capacitor structure.

Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies and for many other purposes.

An inductor is a passive two-terminal electrical component that stores energy in its magnetic field. For comparison, a capacitor stores energy in an electric field. Any conductor has inductance. An inductor is typically made of a wire or other conductor wound into a coil, to increase the magnetic field.

A relay is an electromagnetic switch that uses low voltage primary circuits to close and open high voltage circuits.

Fuses are strips of metal or pieces of wire designed to melt when excessive current passes through (in a short circuit, for instance).

Switches are devices for closing and opening electric circuits.

The circuits in electrical appliances are often printed circuits, on printed circuit boards (PCBs). These are fitted with electrical components. Many appliances also contain small, complex integrated circuits – often called microchips (or chips) – made from silicon wafers (very thin pieces of silicon). They act as semiconductors, which can be positively charged at certain points on their surface and negatively charged at other points (from ‘Professional English in Use. Engineering’).

Exercise 50. Answer the following questions.

1. What is the difference between active and passive elements?

2. What active elements do you know?

3. What passive elements do you know?

4. What electrical supply are there? What are the differences between them?

5. What is the function of an electron tube?

6. What is the structure of a transistor?

7. How much power does a transistor operate on?

8. What is the function of a transistor?

9. What is a thermistor?

10. What is the function of a resistor?

11. What can you tell about the structure of a capacitor?

12. What is a capacitor used for in electronic circuits?

13. What is an inductor?

14. What is the function of a relay?

15. What is an integrated circuit?

Exercise 51. Complete the text about electronics by choosing a word from the box.

semiconductor transistors diodes electrons devices integrated circuits capacitors silicon resistors germanium

Electronic circuits are built from basic components. ________ are the most important components. They can be used to amplify the strength of a signal by converting a weak signal into a stronger one or to switch other circuits on or off. ________ reduce the flow of _______ through the circuit, adding resistance to that circuit. ________ function as electronic valves allowing current to flow in only one direction. __________ store electricity in order to smooth the flow. They can be charged and discharged. The two most common capacitors are ceramic and electrolytic. Most electronic devices use ________ or microchips. Inside an IC is a very small piece of _________ with circuits built in. today, semiconductors are usually made of ________ which is cheaper and easier to manufacture than _________. Researchers are constantly trying to reduce the size of transistors in order to reduce the size of _______.

Listening

Exercise 52. (Track 3). Listen and label the diagram with the words below.

battery cables controller lamps solar panel

Exercise 53. (Track 4). Listen and match the items with their specifications.

1. solar panel a) 12V 8W

2. controller b) DC

3. battery c) 5A

4. lamps d) 60W

5. electric(al) current e) 12V 100Ah

Language work. Describing functions.

Present simple	What does an inductor do? It stores energy in its magnetic field.
For + Verb-ing	What is a switch used for? It is used for closing and opening electric circuits.
To + infinitive	Aswitch is used to close and open electric circuits.
Act as + noun	A transistor acts as an oscillator, amplifier, photocell or switch.

Exercise 54. Work in pairs. Make questions and answers about the functions of some circuit components.

Example: 1. A: What’s a generator used for?

B: It is used for converting mechanical energy into electrical one.

2. B: What’s the function of a battery?

A: It is used to convert chemical energy into electrical one.

Student A: switch, transistor, diode, electron tube, thermistor.

Student B: fuse, resistor, relay, capacitor, integrated circuit.

Jigsaw reading and speaking

Exercise 55. Work in small groups. Divide into 3 groups.

Stage 1. Read the text of your group, write down key words from the text, translate them and explain their meaning in English. Complete the table below with the information from your text.

Stage 2. Tell other groups about the text you have read. While listening other groups complete the table with appropriate information.

Electrical Meter	Symbol	Description or structure / Operation	Function
Galvanometer
Ammeter
Voltmeter

THE GALVANOMETER (Group A)

The galvanometer (symbol: or ) is the main component in analog meters for measuring current and voltage. A common galvanometer consists of a coil of wire mounted so that it is free to rotate on a pivot in a magnetic field provided by a permanent magnet. The basic operation of the galvanometer uses the fact that a torque acts on a current loop in the presence of a magnetic field. The torque experienced by the coil is proportional to the current in it: the larger the current, the greater torque and the more the coil rotates before the spring tightens enough to stop the rotation. Hence, the deflection of a needle attached to the coil is proportional to the current. Once the instrument is properly calibrated, it can be used in conjunction with other circuit elements to measure either currents or potential differences (from ‘Physics for Scientists and Engineers’).

THE AMMETER (Group B)

A device that measures current is called an ammeter (symbol: ). The charges constituting the current to be measured must pass directly through the ammeter, so the ammeter must be connected in series with other elements in the circuit. When using an ammeter to measure direct currents, you must connect it so that charges enter the instrument at the positive terminal and exit at the negative terminal. Ammeters are connected in series to the components through which the current to be measured flows. Ideally, an ammeter should have zero resistance so that the current being measured is not altered. Because any ammeter always has some internal resistance, the presence of the ammeter in the circuit slightly reduces the current from the value it would have in the meter’s absence (from ‘Physics for Scientists and Engineers’).