Technical text for listening. Технические тексты для аудирования

83 3.6. Electric Circuits An electric circuit is an unbroken (1) conducting path from, and back to, a power (2) supply. It has three main parts: the power supply, the conductor, and the (3) load. The power is (4) provided by a generator or battery, the conductor carries the current, and the load is an electric (5) device such as a lamp. 3.7. Waves Some waves transport energy (1) through matter by causing the matter to vibrate. There are two types of such waves. Transverse ((2) crosswise) waves cause the tiny particles that make up matter to vibrate at right (3) angles to the directions of the wave. Longitudinal ((4) lengthwise) waves cause the particles to "ripple" in the same direction as the waves. Electromagnetic waves, such as X-rays, do not need to vibrate matter in order to (5) pass energy on. 3.8. What is Sound? Sound travels in waves, but it is not part of the electromagnetic spectrum like (1) light waves and radio waves. Sound is produced when (2) matter vibrates. The (3) frequency of these vibrations is measured in units called hertz (Hz). The term frequency refers to the number of waves produced (4) per second. It is variations in frequency that produce different pitches (high and low sounds). The limits of human (5) hearing are 20 Hz and 20,000 Hz. 3.9. Using sound A musical (1) note is characterized by regular sound waves of a (2) particular frequency. Different musical instruments may produce notes of the same frequency that sound completely different. This is because (3) additional notes, called harmonics, sound when the instrument is played. Each instrument has its own (4) unique set of harmonics created by the way the instrument is constructed and played. It is the (5) arrangement of these harmonics that enables us to distinguish between different sounds of the same frequency. 3.10. Lasers The word laser stands for "Light (1) Amplification by Stimulated Emission of Radiation." A laser is a device for converting (2) ordinary light into and intense (3) narrow beam. The laser passes an electric (4) current through a material, which can be a solid, liquid, or gas. Some atoms of the material take in energy and give off quanta (packets of radiation). This (5) causes other atoms to give off quanta. These bounce back and forth between mirrors and are fired out as light of a single (6) wavelength. 3.11. Electronics Electronics is a new (1) branch of physics, and one that plays an (2) increasingly important part in our lives. It is concerned with the use of electricity to produce signals that (3) carry information and control devices such as computers. These devices contain electric (4) circuits through which electric current flows. The controlling parts in a circuit are called (5) components, and these include diodes and transistors. Components can (6) amplify currents, switch them on and off, or change their direction. 3.12. James Watt (1736-1819) The Scottish (1) inventor James Watt improved the design of the early (2) steam engine, ensuring that it could be used successfully throughout industry. He refined the steam engine designed by the English engineer Thomas Newcomen (1663-1729) and made it more (3) efficient. Watt's work helped to bring about the industrial revolution in Britain. The new Watt steam engines (4) provided much of the power for Britain's industries during the 1800s. The watt (W), the unit of work or power,