Its meaning is the number of times that a substance completes periodic changes in 1s, which is called frequency, which is usually represented by the letter f and the physical unit is Hz.

Frequency is the number of times to complete periodic changes in unit time, and it is a quantity to describe the frequency of periodic motion. It is usually represented by the symbol F or V, with the unit of one second and the symbol s- 1. In order to commemorate the contribution of German physicist Hertz, people named the unit of frequency Hertz, abbreviated as "Hertz", and the symbol was Hertz. Every object has a frequency independent of amplitude, which is determined by the nature of the object itself and is called the natural frequency. The concept of frequency is not only used in mechanics and acoustics, but also in electromagnetism, optics and radio technology.

Frequency in physics:

The number of times a substance completes a periodic change in 1 s is called frequency, which is often expressed by F.

In physics, the unit of frequency is hertz (Hz), and it is also commonly used as kilohertz (kHz) or megahertz (MHz) or GHz. 1kHz= 1000Hz， 1 MHz = 100000hz 1 GHz = 1000 MHz。 The frequency f is the reciprocal of the period t, that is, f =1/t.

The electricity used in China is sinusoidal alternating current with a frequency of 50Hz, which means that it makes 50 periodic changes in one second.

In addition, the sound we hear is also a wave with a certain frequency. The frequency range of human hearing is about 20-20-20000HZ. Beyond this range, our ears will not notice it.

Frequency in mathematics:

Under the same conditions, n experiments were carried out. In these n experiments, the frequency nA of event A is called the frequency of event A. The ratio of nA/n is called the frequency of event A, and it is denoted as fn(A).

1. When the number of repeated experiments n increases gradually, the frequency fn(A) shows stability and gradually stabilizes at a certain constant, which is the probability of event A. This "frequency stability" is also called statistical regularity.

2. Frequency is not equal to probability. According to Bernoulli's theorem of large numbers, when n approaches infinity, frequency fn(A) approaches probability P(A) in a certain sense.

Frequency calculation in mathematics;

Classification: Frequency can be divided into many categories, such as power frequency, audio frequency, tidal frequency, angular frequency, angular frequency, statistical frequency, etc.

Doppler effect:

Frequency-related, we often think of "Doppler effect"

For example, when the ambulance approaches, the sound is getting louder and louder; And the sound is getting lower and lower when the car leaves. You may not realize that this phenomenon belongs to the same principle as the color Doppler ultrasound used in hospitals, that is, the "Doppler effect".

The Doppler effect was named in memory of Austrian physicist and mathematician Christian John Doppler, who first proposed this theory in 1842. The main content is that the wavelength of the object radiation changes due to the relative motion between the wave source and the observer. In front of the moving wave source, the wave is compressed, the wavelength becomes shorter and the frequency becomes higher (blue shift); When it is behind the moving wave source, it will have the opposite effect. The longer the wavelength, the lower the frequency (red shift); The higher the speed of the wave source, the greater the effect. According to the red (blue) shift degree of the wave, the speed of the wave source moving along the observation direction can be calculated.

Source:

Web page link

Web page link