Microbuzzer.com · Posted on 29-12-2008 by microbuzzer
The definition of frequency
Unit time to complete the vibration frequency of vibration of objects is described in the frequency of reciprocating motion of the volume, commonly used symbols f or v said that units of seconds -1. To commemorate the contribution of the German physicist Hertz, it is the frequency named Hertz unit, referred to as “Joseph.” Each object has its own nature by the decision had nothing to do with the amplitude of the frequency, called the natural frequency. The frequency of the concept not only in the mechanics, the application of acoustic, electromagnetic and radio technology is also commonly used. Alternating current in the unit time to complete the cyclical changes in the frequency, called the current frequency.
Physics:
Substances in 1 seconds to complete the cyclical changes in the number of known frequency, commonly used f said.
Physical unit of frequency is Hertz (Hz), referred to as Joseph, also commonly used kilohertz (kHz) or megahertz (MHz) or so units GHz. 1kHz = 1000Hz, 1MHz = 1000000Hz 1GHz = 1000MHz. Frequency f is the reciprocal of the cycle T, that is, f = 1 / T, wave speed = wavelength * frequency. Like the electricity used in China is a sinusoidal alternating current, its frequency is 50Hz, which is a matter of seconds to do it 50 times a cyclical change.
In addition, we have heard is also a certain frequency of the waves. Human auditory frequency range of about 20-20000HZ, outside the range of not for us, as perceived by the human ear.
Astronomical tides in the study, because of the activities of the various celestial bodies long to show the inconvenience Hertz unit, the frequency of commonly used units: cph, that is, cycle per hour. The most common such as the M2 tidal cycle is about 12.42 hours, their frequency is usually expressed as 0.08051cph.
Mathematics frequency:
Under the same conditions, a test n, n times in this experiment, the incident occurred A number nA called the incident occurred A frequency. The ratio nA / n as the incident occurred in the frequency of A, and recorded as fn (A).
⒈ when the number of repeat test n gradually increases, the frequency of fn (A) showed stability, gradually stabilized to a constant, the constant A is the probability of events. Such “frequency stability,” which is usually referred to statistical regularity.
⒉ frequency does not equal probability. By the Bernoulli theorem of large numbers, when n tends to infinity when the frequency of fn (A) in a certain sense close to the probability P (A).
English Interpretation: frequency
Mathematical calculation of frequency:
N random events in the trial occurred m times the relative frequency m / n. General physical sciences in the frequency of vibration per second, the frequency can be random, it could be a certainty.
Under certain conditions, the object of the study to observe or test, every time the conditions to achieve group, known as the first test. The result is called the incident. In one experiment, that may occur or may not be the events referred to as random events.
Incident occurred A random probability p (A) is the possibility of events the size of the measure. Its value between 0 and 1. Under certain conditions, to test, if the events of A can not happen, then p (A) = 0; If the event A is bound to happen, p (A) = 1. N With the number of tests increases, the frequency of the possibility of closer to the greater probability, namely:
Where δ is arbitrary small value.
Hydrological phenomena are complex natural phenomena, which appeared impossible to ascertain whether the probability can only be measured through statistical hydrological data to infer the frequency. As a result of the restriction is based, there is always a certain error.
To describe the phenomenon of hydrological random random variable X, are generally continuous. Therefore, X equal to the probability of any number of x is p (X = x). Hydrological calculation of a cumulative frequency curve FX (x) ~ x to describe the statistical characteristics of hydrological variables. Such as the Yangtze River at Yichang station for peak flow was greater than or equal to 80000m3 / s probability p (X ≥ 80000) = FX (80000).
In hydrological calculation, generally in accordance with the measured data through statistical analysis estimated that the frequency of hydrological variables density function fX (x), again on the fX (x) points (see figure), can be obtained cumulative hydrological variable frequency function FX (x):
Hydrological calculation, the habit of the cumulative frequency curve FX (x) referred to as the frequency curve, fX (x) ~ x curve is referred to as the frequency of the density distribution curve.
Doppler effect
A voice even though there is only one constant frequency, but the listener, he sometimes changes. When the wave source and the relative motion between the listener, the listener feel the frequency change in this phenomenon known as the Doppler phenomenon.
Tags: current, frequency, Hz, TECHNOLOGY
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