I. Read and translate the text

The Electromagnetic Spectrum

The basis for all telecommunications channels, both wired and wireless, is the electromagnetic spectrum.

Telephone signals, radar waves, and the invisible commands from a garage-door opener all represent different waves on what is called the electromagnetic spectrum. The electromagnetic spectrum consists of fields of electrical energy and magnetic energy, which travel in waves.

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The “electromagnetic spectrum” of an object has a different meaning, and is instead the characteristic distribution of an electromagnetic radiation emitted or absorbed by that particular object.

All radio signals, light rays, X-rays, and radioactivity radiate an energy that behaves like rippling waves. The waves vary according to two characteristics, frequency and wavelength. The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometers down to a fraction of the size of an atom.

Frequency is the number of times a wave repeats (makes a cycle) in a second. Frequency is measured in hertz (Hz), with 1Hz equal to 1 cycle per second. One thousand hertz is called a kilohertz (KHz), 1 million hertz is called a megahertz (MHz), and 1 billion hertz is called a gigahertz (GHz).Ranges of frequencies are called bands or bandwidths. The bandwidth is the difference between the lowest and highest frequencies transmitted.

For example, cellular phones are on the 800-900 megahertz bandwidth – that is, their bandwidth is 100 megahertz. The wider the bandwidth, the faster data can be transmitted. Low-frequency waves can travel far but can’t carry much information. High frequency waves can travel only a short distance before breaking up, but they can carry much more information.

Thus, different technologies are best suited to different purposes, depending on the frequency range (bandwidth) they are in. Waves also vary according to their length – their wavelength. At the low end of the spectrum, the waves are of low frequency and of long wavelength (such as domestic electricity). At the high end, the waves are of high frequency and of short wavelength (such as cosmic rays).

(By Williams Sawyer Hutchinson. Using Information Technology.)

II. Make up the word combinations. Write sentences with them: