Frequency

The frequency (from Latin frequentia, frequency) is in physics and engineering, a measure of how quickly follow with a recurring task repetitions on each other, eg in a continuous oscillation. The frequency is the inverse of the period.

The unit of frequency is the SI derived unit with the special name Hertz ( unit symbol Hz), where 1 Hz = s -1. However, other units are sometimes used, such as min-1 or H -1. At the frequency specification of the numerical value and unit thus indicates the numerical value of how many periods take place within the chosen time unit.

In some operations, the repetition frequency terms, the pulse train frequency or the stroke frequency can be used for three- speed movements.

Definition and nature of the frequency

The frequency of a regularly repeating procedure is defined as the reciprocal of the period:

This is equivalent to the number of periodically repeating events based on the time interval for which this number is valid:

This is sometimes listed as a definition of the frequency.

The definition over an integer number, can the presumption suggests that the frequency would be, only a gradual changeable digital value; but the time interval that applies to the number, here is the continuous size. The frequency is changed arbitrarily fine and meets all the characteristics of an analog quantity.

Frequency of waves

In waves, the frequency of the propagation speed is linked to its wavelength:

Wherein electromagnetic waves, and. It is the vacuum speed of light, the wavelength in vacuum, and the refractive index of the medium. With a wave during its propagation the medium changes, the propagation velocity and wavelength change. Their frequency, however, remains the same.

Frequency in everyday life

For each periodic process in nature and in everyday use frequency can be specified. The day - night cycle is repeated, for example, with a frequency of the human heart has dormant in the body at a repetition rate of approximately 50-90 min -1 ( corresponding to 1-1.5 Hz). In acoustics, the standard pitch with a frequency of 440 Hz is known. The perceived pitch of tones of musical instruments is determined by the frequency of its fundamental vibration. The human ear perceives sound waves true at frequencies between 20 Hz and 20,000 Hz, the upper limit as usual decreases with increasing age.

The accessible by electronic means frequencies of electromagnetic waves in the range between about 100 kHz and a few GHz for the purposes of wireless communication in frequency bands split ( long wave, medium wave, FM, ...). The perceptible to human light is in the range between 400 THz and 750 THz.

Measurement

A number of different gauges are listed under frequency meter. The frequency applies in the digital measurement technology as easy to be measured, since only their vibrations or pulses during an appropriate time to be counted, so that these instruments are then referred to as a frequency counter.

Frequency measurement always requires an accurate time base. For this example, time periods are formed as multiples of the period of an accurate frequency generator, such as a quartz crystal. Even as consumer products have quartz crystals relative error limits of the order 0.001%. Such small error limits are otherwise accessible only with extreme effort or not in metrology.

Frequency spectrum

Reliable, non-discrete vibrations always consist of several superimposed oscillations with different frequencies, as in nature there are no perfect sinusoidal oscillations. This can be explained among other things by the fact that real oscillations have a finite length and are therefore limited by an initial and transient. Also vibrating systems can be disturbed from the outside, which is associated with the introduction of additional frequencies in the vibration. A mathematically precise sine wave is, however, no time limit and undisturbed. The totality of the represented in a vibration frequencies with their amplitudes is called the frequency spectrum. Determining the frequency spectrum of a given vibration is Fourier analysis.

Specific frequencies

Related sizes

Also in other sizes that have the dimension of a rate, that is the SI unit of s -1, but are not frequency, such as the radioactive decay rate, the unit Hertz is not to be used.