# What is Hz – Troubleinthepeace

The concept of frequency is often mentioned when studying waves or forms of communication. So What is the frequency?? What are the most popular frequency bands today? Let’s find out in the detailed information content in the article below of webgiaidap.com Please.

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What is frequency?

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1 What is frequency? Some related concepts2 Frequency calculation formulas3 Common types of frequencies today

## What is frequency? Some related concepts

### What is frequency? What is hz (hertz )?

Frequency is the number of times a phenomenon repeats per unit of time. To calculate the frequency, select a time period and count the number of occurrences of the phenomenon during that time, and then divide this number by the selected time period. Thus, the frequency unit is the inverse of the time unit.

In the international system of units, this unit is the hertz, symbol hz, named after the German physicist – Heinrich Rudolf Hertz. 1 hz indicates the frequency of repetition of the event exactly 1 time per second: 1 hz=1/s

Some of those frequency units are:

Number of revolutions per minute (rpm) (revolutions per minute): used for engine speed. Beats per minute (beats per minute): used for heart rate, musical notes, etc.

### Some related concepts

Hertz (hz): one hz equals one cycle per second Cycle: one complete wave of alternating voltage or current. Alternator: is half of a cycle Duration: the time it takes to make one cycle complete period of the waveform.Audio frequency: from 15hz to 20hz (range of human hearing).Radio frequency: from 30-300hzLow frequency: 300kHz to 3 megahertz (MHz).Medium frequency : 3-30 MHz High Frequency: 30-300 MHz Frequency used to describe the operation of electrical equipment. Some common frequency ranges are: Current frequency usually 50hz or 60hz Inverter drives, using 1-20 kilo hertz (kHz) carrier frequency

High frequency and low frequency

## Formulas for calculating frequency

### Formula based on wavelength

When the wavelength and velocity of the oscillation are known in advance, the frequency will be calculated by the formula:

f=V/λ

In there:

V: is wave speed f: is frequencyλ: is wavelength

### Formula based on electromagnetic waves in vacuum

The formula for frequency in a vacuum also has a formula for calculating in a non-vacuum environment. However, in a vacuum, the wave velocity will not be affected by other factors. So the speed of electromagnetic waves in this medium will be equal to the speed of light. The calculation formula is:

f = C/λ

In there:

C: speed of lightλ: wavelength

### Formulas based on time or cycles

Frequency and time are quantities required to complete a wave oscillation, and they are inversely proportional to each other. The formula when knowing the oscillation time will be:

f =1/T<2>

In there:

T: period time or the amount of time it takes to complete one oscillation.

### Formula based on angular frequency

When knowing the angular frequency of a wave, to calculate the standard frequency of that wave, we apply the formula:

f= / (2)<3>.

In there:

is the angular frequency which is the constant pi= 3.14.

## Types of popular frequencies today

### Screen refresh rate

The phrase “scanning frequency” appears a lot in the specifications of electronic equipment such as televisions, computers, air conditioners, etc. Whether it is an LCD or LED screen, it has a refresh rate. What is the screen refresh rate? is the number of frames that can be played in a time interval of one second. As you know, movies will be played through flipping frames.

Scan frequency on smartphone screen

The more and faster the amount of frames flipped, the better the video quality and the smoother the movements in the video. For example, you have types of screen scanning frequency such as 60hz, 120hz, .. this means that the screen types will have 60, 120, … per second running frames respectively.

### Frequency of sound that the human ear can hear

Sound is a form of energy perceived by human hearing through sensing waves propagating through space, which is received with the eardrum. Normally, humans will be able to hear all kinds of sounds in the range of 20-20000hz. This sequence will have the following characteristics:

Frequencies below 20hz are called infrasound, you can feel them but not hear them. Frequencies above 20000hz are called ultrasonic, you can only feel and not hear them.

See also: What is Hangover – The meaning of the word Hangover

A few cases can still hear this sound in the range of 20-20000hz due to their special location and structure of the eardrum, which makes them have a higher hearing threshold.

### Current frequency

What is the frequency of the current? Household electrical appliances such as televisions, refrigerators, etc. have parameters on the device as 220V/50hz or 220V/60hz. In Vietnam, the most commonly used network is the 50hz frequency, which means that within 1/50s the current will return to its original state. Understand another way in the current will repeat about 50 times.

DC current frequency

The DC current amplitude will have a straight line, have a constant magnitude with time and go in a certain direction. Therefore, the end of the DC current will be zero. Devices that use DC current such as batteries, lighting batteries,….

Alternating current frequency

Alternating current frequency

The amplitude of the alternating current will take the form of a sine moving symmetrically with positive and positive half cycles. Because it moves in the form of a sine wave, the frequency of the alternating current will be 0. In Vietnam, there are two types of current frequency, which are 50hz and 60hz. Similarly, the frequency of 60hz will have a period of 1/60s, the current will return to the first state, in other words, in 1s the current will be repeated about 60 times.

## Instructions on how to distinguish between 50hz and 60hz . frequencies

The biggest difference between the two frequencies 50hz and 60hz is:

Frequency 60hz will have a faster speed than 50hz. Moment of 2 currents with frequency 50hz and 60hz also has a difference, in 1s the r.m.s. value of 60hz will be higher than 50hz For motor and machine generator: engine and generator need to run faster. Therefore, the design will pay more due to the centrifugal force, the friction schedule is higher. With the transmission line and the volume: the impedance (Zr) of the line will increase by more than 20%, so the voltage drop will be higher. Line resistance is reduced by 20%, the effect on the power grid will be stronger. The increased surface effect requires a larger wire cross-section. For transformers, the balance between steel and copper will be different. The steel and copper weight can be reduced, but the window area will not be reduced, so the total rheostat of the transformer will change, and the flux will increase. The 60hz system will save less materials when making electrical equipment but will have more voltage loss on the line. The reason is that when f increases, XL will increase, the loss on the line will increase. The 60hz motor will have to run at a higher speed if running at 50hz, because the mechanical system has to be better designed, more expensive.

## Why does Vietnam use 50hz frequency more than 60hz?

Why does Vietnam use electrical frequency 50hz more than 60hz?

In Vietnam, 50hz current is more commonly used than 60hz for the following reasons:

The frequency of 60hz equipment must have higher insulation, which costs more. Most countries in the world use 50hz current, so it is easy to import frequency compatible devices. easier. This helps the equipment operate more efficiently and safely. In power transmission, the 220V/50hz current will be more economical, the higher the voltage, the lower the drop. The 110V/60hz system is safe in terms of voltage but does not use a ground wire, so when a phase fault occurs, the protective devices will not work because there is no short circuit. Although 220V/50hz voltage is more dangerous in terms of voltage, when it hits phase, electrical equipment will be protected immediately.