Period and frequency of oscillations. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur
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The most important characteristic of mechanical, electrical, electromagnetic and all other types of oscillations is the period-time during which one complete oscillation takes place. If, for example, the pendulum of a walking clock makes two complete oscillations in 1 s, the period of each oscillation is 0,5 s. The period of oscillation of a large swing is about 2 s, and the period of oscillation of a string can be from tenths to ten thousandths of a second.
Another quantity that characterizes oscillations is frequency (from the word "frequent" - a number showing how many complete oscillations per second the clock pendulum, sounding bodies, current in a conductor, etc., make. The frequency of oscillations is estimated by a unit called hertz (abbreviated as : Hz): 1 Hz is one oscillation in 1 s. If, for example, a sounding string makes 440 complete oscillations in 1 s (in this case, it creates the tone "la" of the first octave), it is said that its oscillation frequency is 440 Hz. alternating current electric lighting network 50 Hz At this current, the electrons in the conductors for 1 s flow alternately 50 times in one direction and the same number of times in the opposite direction, that is, they complete 1 complete oscillations in 50 s.
The larger units of frequency are kilohertz (written: kHz) equal to 1000 Hz, and megahertz (written: MHz) equal to 1000 kHz, or 1000000 Hz.
By the frequency of vibrations of the sounding body, one can judge the tone, or pitch of the sound. The higher the frequency, the higher the tone of the sound, and, conversely, the lower the frequency, the lower the tone of the sound. Our ear is able to respond to a relatively small band (section) of frequencies of sound vibrations - from about 20 Hz to 20 kHz. This band contains the entire wide range of sounds created by the human voice and a symphony orchestra: from very low tones, similar to the sound of a beetle buzzing, to the barely perceptible high-pitched squeak of a mosquito. Oscillations with a frequency of up to 20 Hz, called infrasonic, and above 20 kHz, called ultrasonic, we do not hear. And if our ear were able to respond to ultrasonic vibrations, we might be able to hear the vibrations of the pistils of flowers, the wings of butterflies.
Do not confuse the pitch, that is, the tone of the sound, with its strength. The pitch of the sound does not depend on the amplitude, but on the frequency of vibrations. A thick and long string, for example, creates a low tone of sound, that is, it vibrates more slowly than a thin and short string, which creates a high tone of sound. Figure 1 will help you understand this issue.
Fig.1. The higher the frequency of the string, the shorter the sound waves and the higher the tone of the sound.
In electrical and radio engineering, alternating currents are used with a frequency of several hertz to thousands of megahertz. Antennas of broadcasting stations, for example, are fed with currents with a frequency of about 150 kHz to 50-60 MHz. These fast alternating currents are the means by which sound is transmitted over long distances without wires. The entire huge range of alternating currents is usually divided into several sections - subranges. Currents of relatively low frequencies, ranging from 20 Hz to 20 kHz, are called currents of sound (or low) frequency, since they correspond to the frequencies of sound vibrations, and alternating currents with a frequency of 20 kHz or more are called ultrasonic frequency currents. At the same time, currents with frequencies from 100 kHz to 30 MHz are called high-frequency currents, and currents with frequencies above 30 MHz are called ultra-high and ultra-high frequencies.
Remember well the boundaries and names of subranges of frequencies of alternating currents.
Publication: N. Bolshakov, rf.atnn.ru
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